Note: Descriptions are shown in the official language in which they were submitted.
21~795~
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PROCESS FOR PRODUCING ETHYLENE-VINYL
ALCOHOL COPOLYMER AND SHAPED ARTICLES THEREFROM
BACKGROUND OF THE INVENTION
Field of the invention
The present invention relates to a process for producing
ethylene-vinyl alcohol copolymers and a process for producing
shaped articles, and is a divisional of Application Serial No.
2,059,400, filed January 15, 1992.
Description of the prior art
(Part 1) Ethylene-vinyl alcohol copolymers (hereinafter
sometimes referred to as "EVOH") are obtained by saponifying
ethylene-vinyl ester copolymers, particularly ethylene-vinyl
acetate copolymer. In particular, EVOH's having an ethylene
content of 25 to 45 mol~ and an inherent viscosity
(hereinafter referred to as "[~]inh") of 0.099 to 0.110
liter/gram (hereinafter "liter/gram" is expressed as "1/g")
(measured at 30~C using a mixed solvent consisting of water 15
wt~ and phenol 85 wt~), are known and widely used, thanks to
their high gas barrier properties, for food packaging
containers, containers for oils, parts which contact oils and
similar purposes. Demand for these copolymers are expanding
to a great extent in conformity with changing eating habits.
EVOH's having an ethylene content of less than 25 mol~
are expected to be more widely used as products that improve
~1~79~3
.
the water resistance, water absorption property and swelling
property of polyvinyl alcohol. EVOH's having an ethylene
content of at least 45 mol~ are expected to be more widely
used as EVOH resin having excellent flexibility and
moldability. Further EVOH's having an ethylene content of
25 to 45 mol% and having an ~ ]inh exceeding 0.110 l/g are
expected to be more widely used as products having improved
durability and mechanical strength, which will contribute to
improvements of performance in various fields of use. To
summarize, EVOH's having higher or lower ethylene content
than that of known EVOH's, and those having higher degree of
polymerization than that of known EVOH's could exhibit
various excellent performances that cannot be achieved by
the known EVOH's, and development of their inexpensive and
rational production process therefore has been desired.
It is known that, upon copolymerization of ethylene and
vinyl ester by solution polymerization, an alcohol such as
methanol or t-butanol is principally used as the polymeriza-
tion solvent. No disclosure has ever been made that
dimethyl sulfoxide is used as the polymerization solvent in
the production of ethylene-vinyl ester copolymers. In the
known process, where an alcohol such as methanol is used as
polymerization solvent and the desired copolymer should have
a high ethylene content of at least 50 mol~, the resulting
copolymer precipitates at a temperature range of not higher
than 50-C in the reaction zone to make the solution
heterogeneous even in the presence of about 20% by weight of
~ 679S3
the solvent in the zone. This causes inconvenience in
operation, particularly with continuous polymerization. It
-is also known that, with solution polymerization, higher
solvent concentration in the polymerization zone results in
lower degree of polymerization of the resulting polymer. To
obtain a polymer with high degree of polymerization, it is
therefore necessary, where the known solvent of methanol or
the like is used, to take measures that are undesirable from
the standpoint of production efficiency, such as lowering
the polymerization tëmperature, suppressing polymerization
rate and suppressing the amount of methanol added. With co-
polymerization at a high temperature of at least 60~C, heat
of reaction becomes large, and hence it becomes difficult to
maintain a uniform temperature throughout the reaction zone
and there may occur run away reaction particularly with
radical polymerization.
On the other hand, homopolymerization of vinyl acetate
in a solvent of dimethyl sulfoxide is known. See for
example Japanese Patent Publication No. 3999/1961 (USP
3,080,350). There is, however, no description of copolymer-
- ization of ethylene and vinyl acetate, or about how dimethyl
sulfoxide, upon radical copolymerization of ethylene and
vinyl acetate, functions or in~luences the internal
structure of the resulting copolymer.
(Part 2) Known saponification processes for ethylene-vinyl
ester copolymer include a homogeneous saponification process
which comprises using an alcohol solvent such as methanol
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and an alkaline catalyst and a heterogeneous saponification
comprlsing using a solvent of methanol/water or the like and
an alkaline catalyst. In saponification with a solvent of
methanol, the rate of saponification however decreases to a
large extent with increasing ethylene content.
In particular, homogeneous saponification generally
proceeds as follows and is more advantageous than hetero-
geneous saponification from the viewpoint of commercial
production. The EVOH that forms by saponification is, in
the form of solution in methanol, subjected to a primary
processing of extrusion into a non-solvent for the
copolymer, such as water, or a mixed solvent of methanol and
the non-solvent to form strands, chips or the like shapes,
followed by drying thereof. The EVOH thus obtained is then,
in the form of melts or a solution in a specific solvent,
generally subjected to a secondary processing into fiber,
hollow fiber, film, granules or like desired shapes, to give
a finished product. These known processes contain, as
described below, various points to improve.
1) The solubility of an ethylene-vinyl acetate copolymer
in methanol decreases with increasing ethylene content, so
that saponification in a homogeneous phase requires
undesirable conditions such as high temperature and high
pressure.
2) The EVOH that forms by saponification of an ethylene-
vinyl acetate copolymer having an ethylene content lowerthan 25 mol% or higher than 45 mol% has poor solubility in
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21~79~j~
methanol. Particularly in the low-ethylene side, a
homogeneous state with a concentration sufficiently high for
commercial production cannot be maintained even under high-
temperature and high-pressure conditions of at least 100~C,
whereby saponification in a homogeneous state cannot be
conducted.
3) Saponification of ethylene-vinyl acetate copolymer
proceeds slower than that of polyvinyl acetate, thereby
requiring a large amount of catalyst and methanol and, also
caused by the poor solubility of the resulting polymer
mentioned above, severe conditions of high temperature and
high pressure. As a result the production cost increases
with increased raw material cbst and utility cost of steam
and the like and increased equipment cost for reaction
vessel and the like.
Studies made so far show that ethylene-vinyl acetate
copolymers having a vinyl acetate content of not more than
40 mol% are difficult to hydrolyze due to its markedly low
solubility. Accordingly, Bestian (USP 3,344,129) reports
2~ that alcoholysis of such copolymers in methanol or ethanol
proceeds at a very low rate because of the markedly low sol-
ubility of the copolymer in the solvent. Then the reaction
mixture contains both hydrolyzed molecules and unhydrolyzed
molecules and is heterogeneous. According to Bestian, the
Roland process (USP 2,386,347) that comprises using a mix-
ture of an aromatic hydrocarbon and an alcohol as reaction
solvent is effective only with the molar ratio between vinyl
~16795~
.
ester and ethylene (vinyl ester/ethylene) being not more
than 1/5. With a low vinyl acetate content in the polymer,
- the amount of aromatic hydrocarbon required is very large,
which is uneconomical, and the reaction rate is close to 0.
To overcome these problems, Bestian proposes to use a
reaction solvent of an alcohol having 4 to 8 carbon atoms,
thereby improving solubility, and further suggests
employment of higher temperature.
USP 3,080,350 of Imai et al (Japanese Patent Publica-
tion No. 4539/1961) discloses a process which comprises
polymerizing vinyl acetate in an aprotic solvent having a
large polarity, i.e. dimethyl sulfoxide, and subjecting the
obtained polyvinyl acetate to hydrolysis or alcoholysis into
polyvinyl alcohol. The patent however describes nothing
about copolymerization of ethylene and vinyl acetate or
alcoholysis of the resulting copolymer to obtain EVOH. The
patent does not describe about what function dimethyl
sulfoxide performs upon alcoholysis of ethylene-vinyl
acetate copolymer or how it influences the structure of the
resulting EVOH.
Vinson reports that the use of dimethyl sulfoxide as a
reaction solvent leads to an increase in the rate of
saponification of polyvinyl acetate ~J. Chem. Ed. 46, 877
(1969). The process of saponification according to Vinson,
however, proceeds in the presence of a considerably large
amount of water. As a result, when this process is applied
to ethylene-vinyl acetate copolymer, heterogeneous reaction
~167~a~
results since the EVOH that forms is insoluble in water.
USP 3,780,004 by John et al (Japanese Patent Applica-
tion Laid-open No. 71082/1974 discloses a process which
comprises conducting saponification of ethylene-vinyl ester
co-polymer in a solid phase in an aprotic reaction medium
such as dimethylformamide or dimethyl sulfoxide, in
combination with, as occasions demand, a hydrocarbon-based
reaction medium. The patent however does not disclose the
above process being conducted in an homogeneous liquid
phase.
(Part 3) The EVOH obtained by saponification of ethylene-
vinyl acetate copolymer in the presence of sodium hydroxide
catalyst is, in the form of solution in methanol, subjected
to a primary processing of extrusion into a non-solvent for
the copolymer, such as water, or a mixed solvent of methanol
and the non-solvent to form strands, chips or the like
shapes, followed by drying thereof. These shaped articles
thus obtained are then again melt or dissolved and, in the
form of melts (dry processing) or a solution in a specific
solvent (wet processing), generally subjected to a secondary
- processing into fiber, hollow fiber, film, granules or like
desired shapes, to give finished products. This known
process contains, in addition to the afore-described
problems 1), Z) and 3), the following points to improve.
4) EVOH is not provided with sufficient thermal stability
and tends to suffer thermal degradation and form irregular
matter during a long-time drying after the extrusion into
21679~3
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water, which will cause gels to generate during the
secondary processing.
- 5) High-polymerization-degree EVOH's having an [~ ]inh
exceeding the range of 0.099 to 0.110 l/g have high solution
viscosity, so that they readily form gels during drying and
like processes, which remain undissolved upon re-dissolving.
(Part 4) The EVOH's having a high degree of polymerization
as above that form by saponification are, in the form of
solution in methanol, subjected to a primary processing of
extrusion into a non-solvent for the copolymer, such as
water, or a mixed solvent of methanol and the non-solvent to
form strands, chips or the like shapes, followed by drying
thereof. These shaped articles thus obtained are then again
melt or dissolved and, in the form of melts (dry processing)
or a solution in a specific solvent (wet processing or dry-
jet-wet processing), generally subjected to a secondary
processing into fiber, hollow fiber, film, granules or like
desired shapes, to give finished products. This known pro-
cess contains, in addition to the afore-described problems
1) through 5), the following points to improve.
6) In a copolymerization zone of ethylene-vinyl ester and
containing methanol, the degree of polymerization of the
resultant ethylene-vinyl ester copolymer decreases with
increasing amount of methanol present. To suppress the
decrease in the degree of polymerization, unfavorable
process conditions should be employed, such as lowering
polymerization temperature, lowering polymerization rate and
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suppression of the amount of methanol added.
7) Even when attempts are made to obtain EVOH's with a wide
range of ethylene content, by polymerization using methanol,
the content of ethylene has an upper limit so that EVOH with
high ethylene content is difficult to obtain.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to
provide an inexpensive and rational process for producing
ethylene-vinyl esters which is free from the problems
described in (Part 1) and can provide ethylene-vinyl esters
having wider range of ethylene content and degree of
polymerization than those of the known ethylene-vinyl ester
copolymers.
An object of the present invention is to provide an
inexpensive and rational process for producing the known EVOH,
which is free from the problems described in (Part 2).
A still further object of the present invention is to
provide a more inexpensive and rational process, which is free
from the problems described in (Part 3), for producing EVOH
shaped articles by the known process therefor.
Another object of the present invention is to provide an
inexpensive and rational process, which is free from the above
problems described in (Part 4), for producing shaped articles
from EVOH's having wide ranges of ethylene content and degree
of polymerization.
~1~79a3
The above first object can be achieved by providing a
process for producing ethylene-vinyl ester copolymer by
copolymerizing ethylene and a vinyl ester in the presence of
a radical initiator, said process comprising using a dialkyl
sulfoxide as a polymerization solvent.
The above second object can be achieved by providing a
process for producing ethylene-vinyl alcohol copolymer by
saponification of an ethylene-vinyl ester copolymer, said
process comprising using a dialkyl sulfoxide as solvent and
conducting saponification in a liquid phase.
The above third object can be achieved by providing a
process for producing shaped articles of ethylene-vinyl
alcohol copolymer (B) comprising the combination of:
(I) a process which comprises conducting saponification of an
ethylene-vinyl ester copolymer (A) in a liquid phase using
dialkyl sulfoxide as solvent to produce a solution of the
resulting ethylene-vinyl alcohol copolymer (B), and
(II) a process which comprises contacting the above solution
of the ethylene-vinyl alcohol copolymer (B) obtained in the
process (I) with a non-solvent for the copolymer (B) or a
mixed solvent containing at least 20~ by weight of said non-
solvent, to obtain the shaped product.
The above fourth object can be achieved by providing a
process for producing shaped articles of ethylene-vinyl
alcohol copolymer (B) comprising the combination:
(I)' a process which comprises copolymerizing ethylene and a
vinyl ester using dialkyl sulfoxide as polymerization solvent
and in the presence of a radical initiator, to
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obtain a solution of an ethylene-vinyl ester copolymer (A);
(II)' a process which comprises distilling off unreacted
vinyl ester from said solution of said ethylene-vinyl ester
copolymer (A) while -maintaining the viscosity of said
solution at not more than 500 poises;
(III)' a process which comprises conducting saponification
of the solution of said copolymer (A) obtained by the
process (II)' to obtain a solution of the resulting ethylene-
vinyl alcohol (B); and
(IV)' a process which comprises contacting said solution of
said ethylene-vinyl alcohol copolymer (B) obtained in the
process (III)' with a non-solvent for said copolymer (B) or
a mixed solvent containing at least 20% by weight of said
non-solvent.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many
of the attendant advantages thereof will be readily obtained
as the same become better understood by reference to the
following detailed description when considered in connection
with the accompanying drawings, wherein:
FIGURE 1 is a graph with the abscissa showing the
amount of solvent (~ by weight) and the ordinate showing
the inherent viscosity [~ ] (l/g) of EVOH, in Examples 2
through 5 and Comparative Examples 2 through 6;
FIGURE 2 is a graph with the abscissa showing the
polymerization time (hours) (excluding induction period) and
21~ 7g~3
the ordinate showing the solid concentration of EVA
~weight of EVA solid relative to that of polymerization
solution) in solution samples taken during polymerization,
in Example 9 and Comparative Example 11;
FIGURE 3 is a graph with the abscissa showing the
saponification time (minutes) and the ordinate showing the
degree of saponification (DS) of EVOH, in Example 2-2 and
Comparative Example 2-1;
FIGURE 4 is a graph with the abscissa showing the
saponification time (minutes) and the ordinate showing the
DS of EVOH, in Examples 5-1 through 5-4.
FIGURE 5 is a graph with the abscissa showing the
saponification time (minutes) and the ordinate showing the
~ DS of EVOH, in Comparative Examples 5-1 through 5-5.
FIGURE 6 is a graph with the abscissa showing the
ethylene (ET) content and the ordinate showing the ratio
of the rate of reaction with DMSO- saponification system to
that with MeOH-saponification system in Examples 5-1 through
5-4 and Comparative Examples 5-1 through 5-5; and
FIGURE 7 is a graph with the abscissa showing the
ethylene (ET) content and the ordinate showing the [~ ] of
EVOH, Examples 6-1 through 6-5 and Comparative Examples 6-1
through 6-5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the process of the first invention,
ethylene-vinyl ester copolymers the degree of polymerization
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21679~3
of which has not been decreased to a large extent. With the
ethylene-vinyl ester copolymers that form, which are readily
soluble in dialkyl sulfoxide, homogeneous polymerization can
be maintained over a wide range of ethylene content.
Further in the succeeding process for removing unreacted
vinyl ester, the homogeneous solution state can be
maintained by adjusting the concentration of the dialkyl
sulfoxide in the system. These features realize a stable
continuous operation of the process.
Experiments carried out by the present inventors showed
the following facts. Where an attempt was made to obtain an
ethylene-vinyl acetate copolymer (hereinafter sometimes
referred to as "EVA") having an ethylene content of 60 mol~
by reacting ethylene and vinyl acetate at 50~C in a system
comprising 20 parts by weight of methanol and 80 parts by
weight of vinyl acetate, EVA started precipitating in the
polymerization zone already at a stage of low conversion,
thereby causing the polymerization zone to become
heterogeneous. On the other hand, where dimethyl sulfoxide
was used according to the present invention, no formation of
precipitates was observed even at a conversion of about 70~.
Besides, while an EVA having an ethylene content of 32 mol~
and obtained by conducting polymerization at 40~C to a
conversion of 20~ in a system comprising 10 parts by weight
of methanol and 90 parts by weight of vinyl acetate gives by
saponification an EVOH having an [~ ]inh of 0.135 l/g, the
[~ ]inh obtained under the same conditions except for using
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dimethyl sulfoxide solvent, i.e. same polymerization, same
conversion and same ethylene content, was 0.149 l/g. These
facts show that the use of dimethyl sulfoxide in place of
methanol as a polymerization solvent for copolymerizing
ethylene and vinyl ester gives a copolymer having higher
inherent viscosity.
The EVOH obtained by saponifying the ethylene-vinyl
ester copolymer obtained by the process of the present
invention has an [~ ]inh of not more than 0.4 1/g,
preferably not more than 0.35 l/g, more preferably not more
than 0.30 l/g, and at least 0.05 l/g, preferably at least
0.06 l/g, more preferably at least 0.07 l/g.
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According to the process of the first invention,
copolymerization is conducted by adding a radical initiator
to a mixed solution containing a vinyl ester and at least 1%
by weight of a dialkyl sulfoxide, under pressurization by
ethylene. The ethylene content and inherent viscosity of
the obtained copolymer vary depending on the ethylene
pressure, polymerization temperature, polymerization rate,
conversion, composition of the vinyl ester monomer and
solvent used and like po~ymerization conditions. These
conditions should strictly be adjusted for the pur~ose of
obtaining a copolymer having the desired ethylene content
and inherent viscosity.
In the present invention, it is preferred that the
ethylene content of the obtained copolymers be 0.1 to 80
mol%. With an ethylene content of less than 0.1 mol~, the
EVOH obtained by saponification does not produce substantial
effect of improving water resistance and like properties as
compared with those of polyvinyl alcohol. The ethylene
content is more preferably at least 1 mol%, still more
preferably at least 5 mol%, yet more preferably at least 10
mol% and most preferably at least 20 mol~. On the other
hand in a region where the ethylene content exceeds 80 mol~,
the copolymer becomes difficult to dissolve in dimethyl
sulfoxide. More preferred from the viewpoint of solubility
of the copolymer the ethylene content is not more than 70
mol%.
The vinyl esters usable in the present invention are
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vinyl esters of lower aliphatic acids having not more than 5
carbon atoms, the representative example being vinyl ace-
tate, and also vinyl propionate. In the present invention,
ethylenically unsaturated monomers other than ethylene and
vinyl esters may also be used within limits not to impair
the purpose of the present invention. Representative
ethylenically unsaturated monomers are given for example in
"POVAL (revised edition)"(published by Kobunshi Kankokai, on
April 1, 1981) on pages 281-285 and also in the literature
cited therein.
Thus, examples of such monomers are olefins having 3 to
18 carbon atoms; vinyl carboxylates, such as vinyl versatate
and vinyl stearate; alkyl vinyl ethers, such as lauryl vinyl
ether and methyl vinyl ether; (meth)acrylates, such as
methyl (meth)acrylate; acrylamides, such as acrylamide,
methaccrylamide and N,N-dimethylacrylamide; unsaturated
carboxylic acids, their esters and their anhydrides, such as
acrylic acid, crotonic acid, maleic acid, fumaric acid, ita-
conic acid, esters and anhydrides of the foregoing; sulfonic
acid monomers, such as vinylsulfonic acid and acrylsulfonic
acid; cationic monomers, such as dimethylaminoethyl
methacrylate, vinylimidazole, vinylpyridine and vinylsuccin-
imide; vinylene carbonate; allyl alcohol and allyl acetate.
The dialkyl sulfoxide used in the present invention
comprises a lower alkyl group, the carbon number of which is
preferably not more than 3 in view of solubility for the
intended ethylene-vinyl ester copolymer and EVOH. Examples
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of the dialkyl sulfoxide are dimethyl sulfoxide, diethyl
sulfoxide, di-i-propyl sulfoxide, di-n-propyl sulfoxide,
methylethyl sulfoxide and methyl-i-propyl sulfoxide. Among
the above dimethyl sulfoxide is particularly preferred,
since it gives ethylene-vinyl ester copolymers having'high
degree of polymerization, is thermally and chemically safe
and is readily available. The dialkyl sulfoxide used
preferably has a water content of not more than 2% by
weight, more preferably not more than 1~ by weight.
In the present invention, copolymerization proceeds in
the liquid phase. The term "liquid phase" herein means a
substantially homogeneous liquid phase.
It is preferred that the content of dialkyl sulfoxide
in the polymerization zone, i.e. the ratio of the amount of
dialkyl sulfoxide to the sum of the amounts of dialkyl
sulfoxide and vinyl ester, be at least 1% by weight. The
content is more preferably, although depending on the
ethylene content and inherent viscosity of the desired EVA,
at least 3% by weight, most preferably at least 5~ by
weight, in view of heat removal from the polymerization
zone, stability with respect to prevention of abnormal
polymerization, maintenance of homogeneous state of solution
and ease of feeding radical initiator.
If the content of dialkyl sulfoxide is less than 1~ by
weight, the system will substantially become equal to bulk
polymerization, where it is difficult to prevent occurrence
of abnormal polymerization and the like and to feed radical
~167~3
initiator uniformly. There is no specific upper limit to
the content of dialkyl sulfoxide, but it is preferably not
more than 80~ by weight, more preferably not more than 70~
by weight from the viewpoint of production efficiency of the
desired copolymer. Copolymers having an ethylene content of
0.1 to 80 mol~ are produced under an ethylene pressure
properly selected in consideration of the intended inherent
viscosity of the copolymer and polymerization conditions.
The ethylene pressure therefore cannot be definitely
designated, but it is generally in a range of atmospheric
pressure to 100 kg/cm2. The polymerization temperature is,
while being closely related to the intended inherent
viscosity and ethylene content of the copolymer, selected
from a range of about 0 to 80~C. Copolymers with normal
inherent viscosity are obtained at a temperature of 40 to
80~C, while those with higher inherent viscosity are
obtained at a lower temperature, e.g. 40~C or below.
The radical initiators usable in the copolymerization
of the present invention include known azo compounds such as
2,2'-azobisisobutyrontrile, 2,2'-azobis-(4-methoxy-2,4-di-
methylvaleronitrile) and peroxides such as benzoyl peroxide
and isopropyl peroxydicarbonate. The initiators are used in
an amount of 0.001 to 1.0~ by weight based on the weight of
vinyl ester monomer, preferably 0.01 to 0.5~ by weight on
the same basis. Adjusting the amount of the initiator fed
can adjust, as well as the degree of removal of heat of
polymerization, the polymerization rate which influences the
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inherent viscosity of the resulting copolymer and the like.
~ In the present invention, the polymerization can be
conducted by any process such as batch system, semi-batch
system or continuous polymerization, among which, however,
continuous system is preferred in view of removal of heat of
polymerization, stability of qualities of the copolymer,
stability of polymerization zone and other factors.
The homogeneous solution comprising the copolymer
produced, unreacted vinyl ester monomer, ethylene, dialkyl
sulfoxide and a trace amount of initiator are subjected, if
necessary to deactivation treatment of the initiator, then
to recovery treatment of the dissolving ethylene in the so-
lution, and then sent to the succeeding process for recovery
of unreacted vinyl ester monomer. The recovery can be
accomplished by adding an amount of dialkyl sulfoxide to
maintain the viscosity of the solution within a specific
range and recovering the vinyl ester monomer in a substan-
tially homogeneous liquid phase. The viscosity maintained
is preferably not more than 500 poises, more preferably not
more than 300 poises, most preferably not more than 100
poises. The lower limit of the viscosity is generally about
1 poise, although not strictly restricted thereto. The
recovery operation is preferably conducted, in consideration
of thermal stability of vinyl ester monomer, by maintaining
the bottoms temperature at not more than 100~C, more pre-
ferably not more than 80-C and under atmospheric pressure or
reduced pressure (in either case, not higher than the boil-
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~1679~3
ing point of the vinyl ester used). It is also one of the
preferred embodiments of the present invention to recover
- vinyl ester monomer such as vinyl acetate at a low tempera-
ture and under atmospheric pressure by adding the lower
alcohol that is to be used as a reaction agent for the
succeeding saponification and thus utilizing azeotrope of
the vinyl ester monomer and the lower alcohol, particularly
methanol. The recovery may be conducted with a stirred-tank
system, column system or thin membrane evaporator, among
which preferred are column system and thin membrane
evaporator in view of recovery efficiency, equipment cost
and adaptability to continuous operation. Unrecovered vinyl
ester monomer may be a factor for coloration in the
succeeding saponification, and hence the content of the
vinyl ester monomer after having passed the recovery system
is preferably reduced to not more than 0.5% by weight, more
preferably not more than 0.2~ by weight.
The ethylene-vinyl ester copolymer, such as EVA,
obtained by the present invention can be converted by sapo-
nification to the corresponding EVOH. The saponification
may be conducted by the known alkaline saponification or
acid saponification, but most suitably by saponification in
methanol solvent in the presence of alkaline catalyst such
as sodium hydroxide or sodium methylate. The methanol used
for saponification may contain the dialkyl sulfoxide such as
dimethyl sulfoxide used in the polymerization.
Next described in detail is the process for producing
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2 1 ~953
EVOH of the present invention that achieves the afore-men-
~ tioned second object. This process realizes far accelerated
saponification as compared with conventional processes.
This process, which is one of the present invention, can
rationally solve the afore-mentioned problem Z) and realize
a low production cost. Thus, the present invention uses a
reaction solvent of dialkyl sulfoxide in place of the known
methanol and effectively utilizes the specific dissolving
behavior of sald solvent against ethylene-vinyl ester
copolymers and EVOH's, thereby realizing proceeding of
reaction always in a homogeneous state even when the
ethylene content and inherent viscosity of the resulting
copolymer are extended beyond the usual specification.
While the process of the present invention is carried
out by homogeneously dissolving an ethylene-vinyl ester
copolymer in a mixed solvent of a dialkyl sulfoxide and a
lower alcohol, an extensive study made by the present inven-
tors revealed that the rate of saponification of ethylene-
vinyl ester in the present invention is higher than that20 with a single solvent of lower alcohol. Ethylene-vinyl
ester copolymers generally have lower reaction rate than
that of the vinyl ester homopolymers, and the saponification
thereof should therefore employ undesirable conditions such
as increasing the reaction temperature and increasing the
amount of alkaline catalyst added. By employing the
process of the present invention, reaction under milder
conditions has become possible.
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216~9~3
In the known usual process comprising using a single
~ solvent of lower alcohol, saponification in a homogeneous
system can only be conducted, because of low solubility of
the resulting EVOH in the lower alcohol, by elevating the
reaction temperature, thereby increasing the solubility. By
the restriction with respect to solubility, it is very
difficult, or sometimes practically impossible, in the known
process to saponify by alcoholysis in homogeneous state an
ethylene-vinyl ester copolymer having an ethylene content of
not more than 2~ mol~ or not less than 45 mol~. The present
invention provides a solution also to such a situation.
Dialkyl sulfoxides are good solvent both for ethylene-vinyl
ester copolymers and EVOH's, so that the reaction zone can
be maintained homogeneous without increasing the reaction
temperature and prevent undesirable phenomena such as
increased deactivation of catalyst and thermal degradation
of the copolymers.
The saponification of the present invention proceeds in
the liquid phase. The term "liquid phase" herein means
substantially homogeneous liquid phase.
In the reaction zone of the present invention, lower
alcohol ester of aliphatic acid such as acetic acid forms by
reaction, and hence it becomes necessary for the purpose of
increasing the saponification degree to shift the saponifi-
cation equilibrium to the formed product side. For this
reason, it is desired to efficiently distill off the ester
used, e. g. methyl acetate. An extensive study made by the
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~iL67~S3
.
present inventors revealed that dialkyl sulfoxide present in
the reaction zone has the effect of increasing efficiency of
separating vinyl ester and lower alcohol. The mixture may
be removed by distillation by either distilling off under
reduce pressure and in tank system or, in column system,
conducting saponification while introducing the ethylene-
vinyl ester copolymer dissolved in dialkyl sulfoxide through
the middle stage of a reaction column and blowing alcohol
vapor through the bottom stage, and at the same time distil-
ling off lower alcohol and the alcohol ester of aliphahtic
acid from the top stage. The use of this effect can
markedly reduce the number of stages and reflux ratio of
distillation column, thus contributing to reduction in
equipment cost and utility cost.
The degree of saponification of the EVOH can be select-
ed depending on the intended use of the copolymer and is
preferably at least 20%, more preferably at least 50~.
(When the degree of saponification is expressed in "%", the
"%" means "% by mole", which will apply hereinafter.) For
use in fields requiring high gas barrier properties, the
saponification degree is preferably at least 99.0% and more
preferably at least 99.5%.
The dialkyl sulfoxide used in the present invent~on
comprises a lower alkyl group having, preferably, not more
than 3 carbon atoms in view of solubility for ethylene-vinyl
ester copolymers and EVOH's. Examples of the dialkyl sulf-
oxide are dimethyl sulfoxide, diethyl sulfoxide, di-i-propyl
~ 7~3
sulfoxide, di-n-propyl sulfoxide, methylethyl sulfoxide and
~ methyl-i-propyl sulfoxide, among which dimethyl sulfoxide
and diethyl sulfoxide are preferred in consideration of
thermal and chemical stability, price and the like.
Dimethyl sulfoxide is particularly preferred based on
overall judgement. The dialkyl sulfoxide is used in any
amount insofar as it homogeneously dissolves ethylene-vinyl
ester copolymer and EVOH. In consideration of the solution
viscosity and the like, the amount is preferably, in terms
of the concentration of ethylene-vinyl ester copolymer in
the dialkyl sulfoxide solution, 0.1 to 70% by weight based
on the sum of the weights of ethylene-vinyl ester copolymer
and the dialkyl sulfoxide, more preferably 1 to 50~ by
weight on the same basis
In the present invention, lower alcohol is used as a
reaction agent for saponification. The production of EVOH's
by saponification of the corresponding ethylene-vinyl ace-
tate copolymers is known. The rate of this saponification
is generally lower than that of polyvinyl acetate, which is
Z~ homopolymer of vinyl acetate, and tends to decrease with
increasing content of ethylene. Extensive study by the
present inventors on saponification of ethylene-vinyl ester
copolymers has revealed that it is desirable to use lower
alcohols for the saponification and in particular monohydric
alcohols having 1 to 5 carbon atoms. Examples of lower
monohydric alcohols having 1 to 5 carbon atoms are methanol,
ethanol, n-propanol, n-butanol, i-butanol, n-amyl alcohol
-24-
9 ~ ~
and i-amyl alcohol. Among the above, methanol or ethanol is
~ suitably used in view of solubility for ethylene-vinyl ester
and the like, and particularly preferred is the use of
methanol in view of reaction rate. The lower alcohol is
used in any amount insofar as it is sufficient for producing
EVOH by saponification of the corresponding ethylene-vinyl
ester copolymer. The amount is generally 1.0 to 50 molar
equivalents based on the theoretical mole calculated from
the average molecular weight of the ethylene-vinyl ester
copolymer, and is preferably 1.5 to 30 molar equivalent,
more preferably 2.0 to 20 molar equivalents on the same
basis in view of reaction equilibrium of saponification,
after-treatment cost for the alcohol fed and like factors.
The saponification of the present invention is
conducted in the presence of an alkaline catalyst. The
alkaline catalysts usable in the invention are known ones
used in the saponification by alkaline catalyst of polyvinyl
acetate or ethylene-vinyl acetate copolymers. Examples of
such catalysts are alkali metal hydroxides, such as sodium
Z~ hydroxide, potassium hydroxide and lithium hydroxide; alkali
metal alcolate, such as sodium methylate and potassium t-
butoxide; strong base amine, represented by l,8-diazabi-
cyclo[5,4,0]-undecene-7 (DBU); alkali metal carbonates and
alkali metal hydrogencarbonates, among which sodium
hydroxide is preferred because of easy handling and low
price. The amount of catalyst used varies depending of the
intended degree of saponification and reaction temperature,
-25-
9 ~ :i - -'- - '
but is generally in a range of 0.001 to 1.0 mole per mole
calculated from the average molecular weight of the ethylene-
vinyl ester copolymer.
The reaction temperature for the saponification of the
present invention may optionally and as required selected
from a range of room temperature to about 150~C, but
preferably 40 to 120~C, more preferably 50 to 100~C for the
purpose of achieving high reaction rate under atmospheric
pressure.
The saponification of ethylene-vinyl ester copolymer
may be conducted by stirred-tank system, column system or
the like. One preferred embodiment is a column system which
comprises introducing dialkyl sulfoxide having dissolved the
copolymer through the middle stage of a reaction column and
blowing alcohol vapor through the bottom stage, and
withdrawing byproduct alkyl ester, e.g. methyl acetate, from
the top stage.
It is preferred in the present invention that the
alcoholysis be conducted under the condition where oxygen
has been substantially removed; for example with an oxygen
concentration of not more than 5 x 10~~ mol/l, since, then,
decrease in the degree of polymerization is suppressed. For
maintaining the oxygen concentration at the above level or
below, the reaction zone is either substituted by nitrogen
gas with at least 99.9% purity or heated at 60~C or above
and then substituted with nitrogen or argon.
-26-
~679$3
.
Now described is the process for producing shaped
~ articles of EVOH that achieves the afore-recited third
object of the present invention.
The process of the invention comprises obtaining EVOH
(B) in a homogeneous solution by dissolving the correspond-
ing ethylene-vinyl ester copolymer in a mixed system of a
dialkyl sulfoxide and a lower alcohol as a reaction agent,
to conduct saponification in the presence of alkaline
catalyst. The homogeneous solution can be, after being, if
necessary, subjected to concentration adjustment, without
being subjected to the known primary processing of EVOH (B)
into strands or chips, directly and in the form of solution
as it is, subjected to what is known as "secondary"
processing into optional shape, such as fiber, hollow fiber,
film, sheet or granules, by wet or dry-jet-wet system. The
process of the present invention can rationally eliminate
the afore-mentioned problems associated with the usual pro-
cess and realize a low production cost. The process of the
present invention uses, in lieu of known methanol, a dialkyl
sulfoxide as a reaction solvent and utilizes the specific
dissolution behavior of the solvent against the above copo-
lymers (A) and (B), thereby assuring proceeding of reaction
always in a homogeneous state even when the ethylene content
and degree of polymerization of the copolymer extend beyond
the usual specification. Stable operation is then achieved.
Moreover, since the copolymer (B) is, without being
isolated in the course of processes, sent in the form of
-27-
-
2167g~
solution to the final processing step, deterioration in the
reaction zone and/or upon processing is minimized, whereby
stable quality is obtained. The saponification conditions
are the same as described above.
The solution of the copolymer (B) obtained is, after
being confirmed for the saponification degree of the
copolymer (B), subjected to neutralization to deactivate the
catalyst and, as required, subjected to adjustment of the
concentration of the copolymer (Bj. Dialkyl sulfoxides
generally have higher bolling point than those of lower
alcohols and aliphatic acid lower alcohol esters, and hence
the copolymer (B) may be obtained as a solution in dialkyl
sulfoxide, which may or may not contain lower alcohol and
aliphatic acid lower alcohol ester. The solution of the
copolymer (B) in the dialkyl sulfoxide thus treated is sent
to shaping process and contacted with a non-solvent for the
copolymer (B) or a mixed solvent containing at least 20~ by
weight of the non-solvent, thereby being formed into fiber,
hollow fiber, film, sheet, granules, strands, spheres or
other desired shapes, by wet or dry-jet-wet system. If the
non-solvent content is less than 20 ~ by weight, the amount
of the copolymer (B) dissolved in the mixed solvent will
increase, whereby wet or dry-jet-wet processing utilizing
coagulation becomes incomplete. The content of the non-sol-
vent is preferably at least 40% by weight, more preferably
at least 50~ by weight for the purpose of achieving complete
coagulation of the copolymer (B). The coagulation tempera-
-28-
~16795~
ture varies depending on the shape to form, but it
isgenerally in a range of -20 to 100~C, preferably -10 to
50~C. Further in the present invention, the above copolymer
(B) solution in dialkyl sulfoxide may for example be extrud-
ed onto a base material, and then the extrudate be contacted(e.g. by immersion) with a non-solvent for the copolymer (B)
or a mixed solvent containing at least 20% by weight of the
non-solvent, to give shaped articles.
The above shaped articles obtained by wet or dry-jet-
wet processing may further be processed. Thus, the granules
and spheres as they are, and the strands, after being cut topellets having a desired shape, may by processed into fiber,
hollow fiber, film, sheet, bottles or like desired shapes,
by melt molding, wet processing, dry processing or dry-jet-
wet processing.
Examples of the non-solvent for copolymer (B) are, al-
though their effect varies depending on the ethylene content
of copolymer (B), solvents having compatibility with dialkyl
sulfoxide, e.g. water; lower alcohols, such as methanol and
ethanol; esters, such as methyl acetate and ethyl acetate;
ketones, such as acetone and diethyl ketone; and ethers,
such as ethylene glycol dimethyl ether; and mixtures of the
foregoing. For copolymers (B) with low eth~lene content,
generally effective are alcohols represented by methanol,
ketones such as acetone and esters such as methyl acetate.
On the other hand, for copolymers (B) with high ethylene
content, water and esters such as methyl acetate are
-29-
~167Y5~
.
effective. Employment of this shaping process of wet or dry-
jet-wet system prevents formation of gels and irregular
matters caused by thermal degradation and encountered during
processing including drying by conventional process, and
realizes improvement of product performances. Examples of
the solvent usable in combination with the above non-solvent
are dialkyl sulfoxides, particularly dimethyl sulfoxide.
Shaped articles obtained by the above process can be
used for various purposes, including high-performance EVOH
fiber having improved water resistance, EVOH hollow fiber
having excellent permeability performances and used for
artificial kidney and the like, high-performance films for
optical uses, films for industrial uses, gas-barrier
packaging materials having good thermal stability, sealants
and biodegradable material utilizing good compatibility with
starch.
The copolymers (B) formed into the above various shapes
are subjected to extraction and washing off of the solvent
dialkyl sulfoxide, deactivated catalyst and the like and
then dried to give finished products.
Lastly, the process for producing EVOH shaped articles
of the present invention that achieves the afore-mentioned
fourth object of the present invention.
In this process of the present invention, all of
polymerization process (I)', process (II)' for removal by
distillation of remaining monomer, saponification process
(III)' and process (IV)' of contacting with non-solvent are
-30-
2167953
.
the same as already described.
The process of the present invention uses, in lieu of
known methanol, a dialkyl sulfoxide as a reaction solvent
and utilizes the specific dissolution behavior of the
solvent in the polymerization zone, thereby rendering it
possible to produce copolymers with their degree of polyme-
rization having decreased to a lesser extent than the case
with conventional process. This process assures proceeding
of reaction always in a homogeneous state even when the
ethylene content and degree of polymerization of the~copoly-
mer extend beyond the usual specification, thus realizing
stabilization and shortening of processes. Moreover, the
copolymer (B) is, without being isolated in the course of
processes, subjected to ~eaction under mild conditions and
then directly to the final processing of wet or dry-jet-wet
processing to give finished product. Since the number of
processes is thus reduced, (thermal) deterioration of the
copolymer upon processing is minimized, whereby stable
quality is obtained.
The process of the present invention establishes, based
- on detailed study by the present inventors, an ethylene-
vinyl ester copolymerization system with a dialkyl sulfoxide
solvent, where decrease in the degree of polymerization is
smaller than with the known methanol solvent system [process
(I)']. In this copolymerization system, it is possible to
maintain homogeneous reaction systems over a wide range of
ethylene content, and in the succeeding process of removing
-31-
~1~ 7~5~
unreacted vinyl ester [process (II)'] the homogeneous
solution condition can be, as it is, maintained by adjusting
- the concentration in the system by the dialkyl sulfoxide to
a solution viscosity of not more than 500 poises, whereby
stable continuous operation of the process is realized.
The process (III)' in the process of the present inven-
tion comprises conducting saponification in a homogeneous
solution system comprising the copolymer (A) solution in
dialkyl sulfoxide to which a reaction agent of lower alcohol
has been added. Intensive study by the prese~t inventors
has revealed that, in the present invention, the rate of
saponification of the copolymer (A) is higher than that with
a single solvent system comprising lower alcohol. As des-
cribed before, copolymers (A) generally have lower reaction
rate of saponification than that of vinyl ester homopolymer,
and the saponification thereof should therefore employ
undesirable conditions such as increasing the reaction
temperature and increasing the amount of alkaline catalyst
added. By employing the process of the present invention,
reaction under milder conditions becomes possible.
In the known usual process comprising using a single
solvent of lower alcohol, saponification in a homogeneous
system can only be conducted, because of low solubility of
the resulting copolymer in the lower alcohol, by elevating
the reaction temperature, thereby increasing the solubility.
By the restriction with respect to solubility, it is very
difficult, or sometimes practically impossible, in the known
-32-
~ 1 5 ~ 3
process to saponify by alcoholysis in a homogeneous state a
copolymer (A) having an ethylene content of not more than 25
mol~ or not less than 45 mol~. The present invention
provides a solution also to such circumstances. Dialkyl
sulfoxides are good solvent both for copolymers (A) and
copolymers (B), so that the reaction zone can be maintained
homogeneous without increasing the reaction temperature and
avoid undesirable phenomena such as increased deactivation
of catalyst and thermal degradation of the copolymers.
In the reaction zone of the present invention, lower
alcohol ester of aliphatic acid forms by saponification
reaction, and hence it becomes necessary to shift the
saponification equilibrium to the formed product side. For
this reason, it is desired to efficiently distill off the
aliphatic acid ester. An extensive study made by the
present inventors revealed that dialkyl sulfoxide present in
the reaction zone has the effect of increasing efficiency of
separating aliphatic acid ester and lower alcohol. The use
of this effect can markedly reduce the number of stages and
reflux ratio of distillation column, thus contributing to
reduction in equipment cost and utility cost.
Shaped articles obtained by the above process can be
used for various purposes, including high-performance EVOH
fiber having improved water resistance, EVOH hollow fiber
having excellent permeability performances and used for
artificial kidney and the like, high-performance films for
optical uses, films for industrial uses, gas-barrier
-33-
~1~79~3
packaging materials having good thermal stability, sealants
~ and biodegradable material utilizing good compatibility with
starch.
The copolymers (B) formed into the above various shapes
are subjected to extraction and washing off of the solvent
dialkyl sulfoxide, deactivated catalyst and the like and
then dried to give finished products.
As stated heretofore, the processes of the present
invention can produce the following effects.
Ethylene-vinyl ester copolymers having a wide range of
ethylene content can be obtained. Since the polymerization
zone is maintained in a substantially homogeneous liquid
phase, the resulting ethylene-vinyl ester copolymer and
further the EVOH obtainable therefrom both have uniform
properties and residual monomer can readily be recovered.
Furthermore, there can be obtained ethylene-vinyl ester
copolymers with higher polymerization degree than that with
solution polymerization using methanol.
The rate of saponification is higher than that with
single solvent of lower alcohol; and since the alcohol
- reaction zone is maintained in a substantially homogeneous
liquid phase, the obtained EVOH has uniform properties.
The saponification rate decreases only little with
increasing ethylene content. What is interesting is the
relative rate ratio (the reaction rate with dialkyl
sulfoxide/that with methanol) tends to increase with
increasing ethylene content. The process of the present
-34-
~1~ 7 ~ ~ 3
~ .
invention therefore is very effective for the saponification
of high-ethylene ethylene-vinyl ester copolymers.
Production cost is low, since production process of
EVOH is directly connected to that of shaped articles.
Production cost is low, since production process of
ethylene-vinyl ester copolymer having a wide range of
ethylene content is directly connected to saponification of
the ethylene-vinyl ester copolymer into EVOH and further to
that of shaped articles using the EVOH.
Besides, the EVOH obtained by the process of the
present invention exhibits characteristics inherent thereto,
such as a lower melting point than that of the usual EVOH
obtained by polymerization and/or saponification in a lower
alcohol system. This is apparent from Example 7-1 described
later herein and attributable to the fact that the EVOH of
the present invention has specific stereotactic structure
resulting from DMSO-based polymerization and/or specific
distribution of residual ester groups (i.e. more randomized
distribution) resulting from DMSO-based saponification.
It is expected that proper use of these characteristics
contribute to for example, in melt stretching processing of
EVOH, minimizing generation of gels and irregular matters
caused by thermal degradation, improvement in stretching
speed and stretching ratio, reduction in the number of voids
and cracks, improvement in thic~ness uniformity, realization
of stable processing operation over long period of time and
so forth.
CA 021679~3 1998-10-22
The above-described fact that the EVOH obtained by the
process of the present invention has more randomized (i.e.
sharper) distribution of residual ester groups is indicated by
larger block character.
The EVOH obtained by the process of the present invention
preferably has a block character of at least 0.2, more
preferably at least 0.25 and most preferably at least 0.3.
The block character is calculated by:
Block character = (OH-OAc) /2 (OH) (OAc)
where ~OH-OAc) indicates the ratio of the mole fraction
of dyad of vinyl alcohol moiety-vinyl ester moiety to
the sum of mole fractions of dyads {vinyl alcohol moiety-vinyl
alcohol moiety (Al) + vinyl alcohol moiety-vinyl ester moiety
(A2) + vinyl ester moiety-vinyl ester moiety (A3) }, and (OH)
and (OAc) indicate the mole fraction of vinyl alcohol moieties
and that of vinyl ester moieties, respectively, in dyads and
chains longer than dyad, in the EVOH.
The mole fraction of dyad of vinyl alcohol moiety-vinyl
alcohol moiety (Al) is obtained from the absorption intensity
of the peak in the range of ~ = 45.7-48 ppm in l2C-NMR
spectrum and that (A2) of vinyl ester moiety-vinyl
ester moiety from the absorption intensity of the peak
in the range of ~ = 43.5-45.5 ppm. The mole fraction (A3)
of dyad of vinyl ester moiety-vinyl ester moiety is obtained
by subtracting the above A1 and A2 from the square of the sum
of the mole fractions of vinyl alcohol moieties and vinyl
21679~
ester moieties in the EVOH.
Other features of the invention will become apparent in
the course of the following descriptions of exemplary
embodiments which are given for illustration of the
invention and are not intended to be limiting thereof. In
the Examples that follow, the inherent viscosity, [~ ]inh,
of EVA means that of the EVOH obtained by completely
saponifying EVA ~degree of saponification: at least 99.4%).
1 0
~679~3
EXAMPLES
Example 1
A 3-liter high-pressure autoclave e~uipped with a
stirrer was charged with 252 g of dimethyl sulfoxide
(hereinafter referred to as D~SO) (water content: 0.1% by
weight~, 1,009 g of vinyl acetate (hereinafter referred to
as VAc) (DMSO/VAc = 2/8 by weight) and 0.040~ by weight bas-
ed on the weight of VAc of azobisisobutyronitrile (AIBN) and
the system was sufficiently substituted with ethylene. The
autoclave was pressurized by ethylene to a pressure of 43
kg/cm2G and at a reaction temperature of 60~C, to conduct
polymerization for 5 hours. After the completion of polyme-
rization, 1,200 g of DMSO was added to the polymerization
solution and unreacted monomer was removed by evaporation
(50 mmHg or below, 40~C). The solution had a viscosity of
12 poises when the evaporation started and that of 21 poises
when it finished. The solution after the removal was thrown
into pure water, to cause EVA to precipitate. The
precipitates were washed with water, and the polymer was
heated and boiled in water, to remove unreacted monomer, and
sufficiently dried, to give an EVA having an ethylene
content of 32 mol%, in a conversion of 50~. In 100 g of
methanol, 25 g of the obtained EVA was dissolved, and to the
solution 29.5 g of 10% sodium hydroxide (hereinafter some-
times referred to as NaOH) solution in methanol (hereinafter
referred to as MeOH) was added (NaOHjEVA = 0.2 by moles).
The mixture was kept at 60~C for 0.5 hour and again 29.5 g
~ ~ ~ 7 ~ ~ 3
of the NaOH solution was added. The mixture was kept at
60~C for Z hours to effect saponification. The polymer
solution thus obtained was thrown into an aqueous acetic
acid solution to give precipitates- and the mixture was al-
lowed to stand for 0.5 hour. After dehydration, the polymerwas immersed in the aqueous acetic solution for further 0.5
hour and then in tap water for 0.5 hour. The polymer was
pulverized and sufficiently dried, to give an EVOH.
The EVOH thus obtained had a degree of saponification
of 99.5% and an [~ ]inh of 0.119 l/g. As control (Compara-
tive Example 1) an EVOH having a degree of saponification of
99.5~ and an [~ ]inh of 0.097 l/g was obtained as follows.
The same autoclave as above was charged with 243 g of
methanol, 972 g of vinyl acetate (MeOH/VAc = 2/8 by weight),
and 0.104~ by welght based on the weight of VAc of
azobisisobutyronitrile. The autoclave was sufficiently
substituted with ethylene, polymerization was conducted at
60~C and under ethylene pressure of 41 kg/cm2G for 5 hours.
After the completion of polymerization, the same after-
treatments as with the above DMSO system were conducted to
obtain an EVA having an ethylene content of 32 mol% in a
conversion of 50%. The EVA thus obtained was saponified in
the same manner as with the above DMSO system, to give the
desired EVOH. In both of the above two Examples, the
polymerization proceeded always in a homogeneous liquid
phase, which was confirmed by observation on samples of
polymerization solution taken from time to time during the
-39-
~ 679S3
polymerization. The above results suggest that EVOH
obtained by solution polymerization using a solvent of DMSO
has higher inherent viscosity than EVOH obtained-with MeOH
solvent.
Examples 2 through 5
Example 1 was repeated except for changing the amount
of DMSO used, to obtain several EVA's, which were then
saponified in the same manner to give EVA's. The EVA's
obtained (ethylene content: 32 mol%, degree of saponifica-
tion: 99.4 to 99.7%) were tested for inherent viscosity.
As control, bulk polymerization (no solvent) and solution
polymerization with MeOH solvent in the same compositions as
with DMSO solvent were conducted (Comparative Examples 2
through 6). The polymerization conditions were, for the
purpose of confirming the influence of decrease in inherent
viscosity, all set at the same polymerization rate and
conversion, and the ethylene pressure was set such that
copolymers having the same ethylene content would be
obtained (Table 1 and FIGURE 1).
As seen from Table 1, both with DMSO solvent and MeOH
solvent, the ratio of decrease in inherent viscosity
increases with increasing amount of solvent used. FIGURE 1
shows that EVOH obtained with DMSO solvent has higher
inherent viscosity than that with MeOH solvent of the same
amount. In the bulk polymerization of Comparative Example
2, the inside temperature of the polymerization zone tended
to elevate so that careful cooling operation was necessary.
-40-
~1~7$~3
Examples 6 through 8
Example 1 was repeated to conduct polymerization and
- saponification except for using 2,2'-azobis-2,4-dimethyl-
valeronitrile (AVN~ as a polymerization initiator, changing
the amount of DMSO used and employing a polymerization
temperature of 40~C. Here also, as control, bulk polymeri-
zation (no solvent) and solution polymerization with MeOH
solvent in the same compositions as with dimethyl sulfoxide
solvent were conducted. The polymerization conditions were,
for the purpose of confirming the influence of decrease in
inherent viscosity, all set at the same polymerization rate
and conversion, and the ethylene pressure was set such that
copolymers having the same ethylene content would be obtain-
ed (Comparative Examples 7 through 10~. The polymerization
conditions and results are shown in Table 2. As is clear
from comparison of Table 2 with Table 1, even under low
polymerization temperature conditions the influence of the
amount of DMSO solvent on the decrease in the inherent
viscosity of the obtained EVOH is far smaller than that with
MeOH solvent. Here also, like in Examples 1 through 5, with
both of DMSO solvent and MeOH solvent, the polymerization
proceeded always in a homogeneous liquid phase, which was
confirmed by observation on samples of polymerization
solution taken from time to time during the polymerization
(Table 2).
Example 9
Polymerization was conducted in the same manner as in
-41-
~1679~3
Example 1 using 639 g of vinyl acetate (VAc), 160 g of DMSO
(DMSO/VAc = 2/8 by weight) and 0.116% by weight based on the
weight of VAc) of 2,2'-azobis-2,4-dimethylvaleronitrile
(AVN) and at a reaction temperature of 50~C under an
ethylene pressure of 70 kg/cm2G. During the polymerization
polymerization solution was sampled every 1 hour and the
samples were, after addition of polymerization inhibitor,
dried up by evaporation in an infra red drier, to check the
solid content with time. The homogeneity of the reaction
system was examined ~uniformity of EVA concentration and
checking of precipitated EVA). The homogeneous state was
confirmed also by observation of the solution samples.
An EVA was obtained by polymerization under the above
conditions and for 6 hours, in a conversion of 30~. The
solution after the polymerization was subjected to saponifi-
cation in the same manner as in Example 1 (NaOH/EVA = 0.25
by moles, conducte;d twice), and after-treatments in the same
manner, to obtain an EVOH having an ethylene content of 60
mol%, degree of saponification of 99.5~ and an ~ ]inh of
0.088 l/g. FIGURE 2 shows how the solid content changed
with time, i.e. linearly, which indicates that the
polymerization proceeded always in a homogeneous state. The
solution samples were transparent and uniform, with no
pricipitated polymer.
As control, polymerization was conducted with a solvent
of MeOH instead of DMSO, using 624 g of vinyl acetate, 156 g
of MeOH, 0.118% by weight based on the weight of vinyl
-42-
~1~7~a ~
acetate of AVN and at a temperature of 50~C under an
~ ethylene pressure of 62.5 kg/cm2G. With this MeOH system
also, same as with DMSO system, an EVA was obtained by 6
hours' polymerization in a conversion of 30~. The EVA was
saponified in the same manner as in Example 9, to give an
EVOH having an ethylene content of 60 mol~, a degree of
saponification of 99.5% and an [~ ]inh of 0.075 l/g. In the
same manner as with the above DMSO system, the homogenity of
the polymerization zone was studied by monitoring the change
of solid content with time during the polymerization. The
results are also shown in FIGURE 2, which however gave no
good linear relationship because of large dispersion of data
starting already from the stage of low conversion. The
solution samples for this measurement were turbid. These
facts indicate that, in polymerization to obtain high-ethyl-
ene EVA, the use of DMSO as solvent can permit the
polymerization to proceed always in a homogeneous state,
contrary to the case when MeOH is used as solvent.
It is also understood that, also in polymerization to
obtain high-ethylene EVA, the influence of the amount of
DMSO solvent on the decrease in the inherent viscosity of
the resulting EVOH is markedly lower than that with MeOH
solvent.
Examples 10 and 11
Example 9 was repeated except for changing the amount
of DMSO used, to conduct polymerization and saponification.
As control, solution polymerization with MeOH solvent and
-43-
~79~3
.
bulk polymerization were also conducted (Comparative
Examples 11 through 14). Polymerization conditions were all
set such that the same polymerization rate r conversion and
ethylene content would be achieved. The homogeneity of the
systems was studied by monitoring the change of solid
content with time and state of solutions. The results are
shown in Table 3.
As will be understood from Table 3, with DMSO solvent,
polymerization proceeds always in a homogeneous state and
gives a polymer the inherent viscosity of which has decreas-
ed only to a small extent, as compared with polymerization
with MeOH solvent.
Example 12
Polymerization was conducted following the same proce-
dure as in Example 1 with 1371 g of vinyl acetate, 343 g of
DMSO and 0.018~ (based on the weight of vinyl acetate) and
at a reaction temperature of 60~C and under an ethylene
pressure of 3.5 kg/cm2G for 4 hours, to obtain a polymer
having an ethylene content of 5 mol~ in a conversion of 40~.
The polymer was saponified in the same manner as in Example
1 (NaOH/EVA = 0.1 by moles, conducted twice) to give an EVOH
having an [~ ]inh of 0.236 l/g. The solution samples taken
during the polymerization were transparent and homogeneous,
without precipitated polymer.
Example 13
The same EVA solution as that obtained in Example 1
was, after ethylene had been purged, transferred to a 3-
-44-
2~7gS3
liter separable flask. To the solution 1,360 g of DMSO was
added, and residual monomer was distilled off at 50~C under
reduced pressure (not more than 100 mmHg). The mixture
showed a viscosity of 10 poises just after the start of the
distilling off and that of 15 poises when it finished. The
amount of vinyl acetate in the distillate was monitored and,
the distillation was stopped when the distillate became 100~
DMSO. During and after the distillation, the state of the
solution was homogeneous.
Example 2-1
A 5-liter separable flask equipped with a stirrer, a
condenser, a thermometer and a nitrogen gas inlet was charg-
ed with 340 g of an EVA ([~ ]inh = 0.224 l/g), 660 g of MeOH
and 1,700 g of DMSO, and the mixture was stirred with heat-
ing at 70~C to form a homogeneous solution. To the obtained
solution 51.6 g of 3~ sodium hydroxide solution in MeOH was
added and the mixture was subjected to reaction at 70~C for
20 minutes. After the reaction the state of the solution
was homogeneous. Part of the solution was sampled and the
sample was neutralized and then subjected to repeated steps
of precipitation from MeOH and washing. The solid matter
obtained was pulverized and dried to give an EVOH having a
degree of saponification of 97.8~. The saponification was
further conducted for 20 minutes and from the resulting
solution a mixture of MeOH and methyl acetate was, for the
purpose of shifting the saponification equilibrium to the
product side, distilled off by distillation under reduc~d
-45-
~1~7953
pressure. When the distillate outside the zone amounted 780
g, the reaction was terminated by neutralization of the
mixture. The mixture was then after-treated in the same
manner as above to give an EVOH having a saponification
degree of 99.9~. When the reaction was terminated, the
solution showed a homogeneous state.
Example 2-2
In a manner similar to that in Example 2-1, a mixture
of 100 g of an EVA having an ethylene content of 32 mol~
([~ ]inh = 0.111 l/g), 170 g of MeOH and 580 g of DMSO was
stirred with heating at 60~C to give a homogeneous solution.
To the solution 160 g of 3~ sodium hydroxide solution in
MeOH was added and the mixture was reacted at 60~C for 30
minutes. After the reaction, the state of the solution was
homogeneous. During reaction period, the reaction solution
was sampled every hour and each of the samples was treated
as follows. After being neutralized, the sample was added
to 1 g/l acetic acid solution in pure water to precipitate
the polymer, which was then immersed therein for 30 minutes.
Z~ The aqueous acetic acid solution was replaced and the
polymer was immersed therein for further 30 minutes. After
decantation, the polymer was immersed in tap water for 30
minutes.
The polymer was then pulverized and dried to give EVOH.
The relationships between the period of saponification and
the degree of saponification is shown in FIGURE 3. The
degree of saponification was 75~ after 2 minutes after the
-46-
2~67g~3
start of reaction, and the final saponification degree was
98.3%. From the solution obtained by the above reaction for
30 minutes, in the same manner as in Example 2-1, a mixture
of MeOH and methyl acetate was distilled off by distillation
in vacuo for the purpose of shifting the saponification
equilibrium to the product side. When the distillate out-
side amounted 260 g, a solution sample was taken and treated
in the same manner as above, to give a polymer, which showed
a degree of saponification of 99.4%. To the reaction zone
190 g of MeOH was further added and the mixture was sub-
jected to distillation in vacuo in the same manner. When
the distillate amounted to 150 g, the reaction was terminat-
ed by neutralization and the reaction mixture was after-
treated in the same manner to give an EVOH having a degree
of saponification of 99.8%. The ratio by weight between
MeOH and methyl acetate in the distillate just after the
start of distillation was 1:9. During and after the
reaction the solution was in a homogeneous liquid phase.
Comparative Example 2-1
Example 2-2 was repeated except for using MeOH in lieu
of DMSO with the same ratio (molar ratio based on the moles
of VAc component in EVA) of catalyst. The change of the
degree of saponification with time was, in the same manner
as in the above Example, observed. The polymer showed a
saponification degree of 55% after 2 minutes after the start
of reaction and that of 95~ after completion of the 30
minutesi reaction. The results are also shown in FIGURE 3.
~67g5~3
As is apparent from FIGURE 3, the presence of DMSO in combi-
nation can realize accelerated saponification, as compared
with single solvent system of MeOH. From the solution
obtained by the above reaction for 30 minutes a mixture of
MeOH and methyl acetate was distilled off by distillation in
vacuo. The ratio by weight between MeOH and methyl acetate
in the distillate just after the start of distillation was
2:8. A solution sample taken when the distillate outside
amounted 260 g was after-treated and tested for degree of
saponification, which was 96.5%.
From comparison of the ratio by weight of MeOH and
methyl acetate in the distillate of Example 2-1 and that of
Comparative Example 2-1, it is understood that, when
byproduct methyl acetate is distilled off to shift the
saponification equilibrium to the product side, the presence
of DMSO in combination in the reaction zone improves the
separation efficiency of methyl acetate and MeOH, thereby
achieving efficient distilling off of methyl acetate, as
compared with the case with single MeOH system.
During and after the reaction, the solution was in a
homogeneous state, same as the case with the DMSO-added
system.
Example 2-3
In a manner similar to that in Example 2-1, a mixture
Z5 of 100 g of an EVA having an ethylene content of 27 mol~
(~ ]inh = 0.109 l/g), 170 g of MeOH and 550 g of DMSO was
stirred with heating at 60~C to give a homogeneous solution.
-48-
~1~7g~3
To the solution 150 g of 3~ sodium hydroxide solution in
MeOH was added and the mixture was reacted at 60~C for 30
minutes. During and after the reaction, the state of the
solution was homogeneous. During reaction period, the reac-
tion solution was sampled from time to time and treated in
the same manner as in Example 2-1. The EVOH showed a degree
of saponification of 77%, 2 minutes after the start of reac-
tion, and a final saponification degree of 98.6~ r 30 minutes
after the start. From the solution obtained by-the above
reaction for 30 minutes, in the same manner as in Example 2-
1, a mixture of MeOH and methyl acetate was distilled off by
distillation in vacuo for the purpose of shifting the
saponification equilibrium to the product side. When the
distillate outside amounted 250 g, a solution sample was
taken and after-treated to give a polymer, which showed a
degree of saponification of 99.5~. To the reaction zone 190
g of MeOH was further added and the mixture was subjected to
distillation in vacuo in the same manner. When the
distillate amounted to 150 g, the reaction was terminated by
neutralization and the reaction mixture was after-treated in
- the same manner to give an EVOH having a degree of saponifi-
cation of 99.8~. During and after the reaction the solution
was in a homogeneous liquid phase.
Comparative Example 2-2
Example 2-3 was repeated except for using MeOH instead
of DMSO to conduct reaction with the same amount (molar
ratio based on the moles of VAc component in EVA) of
-49-
~1673~3
catalyst. Although the state of the solution was
homogeneous when the reaction started, 5 minutes after the
- start EVOH started precipitation and solidified 10 minutes
after the start. The solid was taken out after 30 minutes,
pulverized in a mixer and after-treated to give an EVOH,
which showed a saponification degree of 96.0~. The EVOH
sample taken out 2 minutes after the start of reaction
showed a saponification degree of 58%.
Example 2-4
In a manner similar to that in Example 2-1, a mixture
of 100 g of an EVA having an ethylene content of 60 mol~
(C~ ]inh = 0.077 l/g), 180 g of MeOH and 760 g of DMSO was
stirred with heating at 60~C to give a homogeneous solution.
To the solution 260 g of 3~ sodium hydroxide solution in
MeOH was added and the mixture was reacted at 60~C for 40
minutes. The EVOH obtained after the reaction showed a
degree of saponification of 97.2~. From the solution
obtained by the above reaction for 40 minutes, in the same
manner as in Example 2-1, a mixture of MeOH and methyl
acetate was distilled off by distillation in vacuo. When
the distillate outside amounted 350 g, a solution sample was
taken and after-treated to give a polymer, which showed a
degree of saponification of 99.0~. To the reaction zone 200
g of MeOH was further added and the mixture was subjected to
distillation in vacuo in the same manner. When the
distillate amounted to 160 g, the reaction was terminated
and the reaction mixture was after-treated to give an EVOH
-50-
~1~79~3
having a degree of saponification of 99.4%. During and
after the reaction the solution was in a homogeneous liquid
phase.
Comparative Example 2-3
5Example 2-4 was repeated except for using MeOH instead
of DMSO to conduct reaction with the same amount (molar ra-
tio based on the moles of VAc component in EVA) of catalyst.
At a temperature of 60-C, the polymer did not dissolve
completely and the mixture remained turbid. After addition
10of the catalyst, the system became homogeneous and reaction
was conducted for 40 minutes. The EVOH after being reacted
for 40 minutes showed a saponification degree of 94.2%.
Mixture of MeOH and methyl acetate was distilled off by
distillation in vacuo. When the distillate outside amounted
15350 g, a solution sample was taken and after-treated to give
a polymer, which showed a degree of saponification of 95.6~.
To the reaction zone 200 g of MeOH was further added and
the mixture was subjected to distillation in vacuo such that
a larger amount was distilled off than the system in Example
202-4 and where DMSO had been present in combination. When
the distillate amounted to 200 g, the reaction was terminat-
ed and the reaction mixture was after-treated and tested for
degree of saponification, which was 97.4~.
Example 2-5
25In a manner similar to that in Example 2-2, there were
used 100 g of an EVA having an ethylene content of 32 mol%
([~ ]inh = 0.111 l/g), 170 g of MeOH, 780 g of diethyl sulf-
-51-
2 1 ~7~3
oxide and 160 g of 39~ sodium hydroxide in MeOH, to conduct
reaction at 60~C for 30 minutes. The sample taken after the
30 minutes' reaction showed a degree of saponifi-cation of
98.0%. After distillation to a distillate amounting 260 g,
an EVOH having a saponification degree of 99.3% was
obtained. After further addition of 190 g of MeOH and the
succeeding distillation to a distillate of 150 g, an EVOH
having a saponification degree of 99.6% was obtained. The
ratio by weight between MeOH and methyl acetate in the
distillate just after the start of distillation was 1:9.
During and after the reaction the solution showed a
homogenous state.
Example 2-6
In a manner similar to that in Example 2-2, there were
used 100 g of an EVA having an ethylene content of 32 molg6
(~7 ]inh = 0.111 l/g), 320 g of ethanol, 580 g of DMSO and
160 g of 3% sodium hydroxide in ethanol, to conduct reaction
at 60~C for 40 minutes. The sample taken after the 40 mi-
nutes' reaction showed a degree of saponification of 96.5%.
After distillation to a distillate amounting 380 g, an EVOH
having a saponification degree of 98.5g6 was obtained. After
further addition of 270 g of ethanol and the succeeding
distillation to a distillate of 220 g, an EVOH having a
saponification degree of 99.5% was obtained. During and
after the reaction the solution showed a homogenous state.
-52-
2 1 ~ 7 9 ~ 3
Example 3-1
A 5-liter separable flask equipped with a stirred, a
reflux cooler, a catalyst liquid inlet and a sampling port
was charged with 328 g (3.95 moles) of an EVA (ethylene
content: 5 mol%, [~ ]inh = 0.181 l/g, 710 g (22.19 moles) of
MeOH and 1,700 g of DMSO and the inside atmosphere of the
flask was replaced by nitrogen gas. Temperature elevation
was started with stirring in an oil bath and the EVA was
dissolved at 60~C. Then, a catalyst solution of 1.58 g
(0.0395 mole) of sodium hydroxide in 50 ml of MeOH was added
at once under nitrogen gas atmosphere to start reaction,
which was allowed to proceed at 60~C for 30 minutes. After
the 30 minutes, a sample was taken out and the EVOH formed
and contained therein was tested for the degree of saponifi-
cation, which was 97.8~. A reduced-pressure distillation
apparatus was connected to the above reactor and further
saponification of the polymer was conducted at a constant
temperature of bottoms of 70~C while byproduced methyl
acetate and MeOH were being distilled off under normal or
reduced pressure. The ratio by weight of methyl acetate/MeOH
- in the distillate just after the start of the byproducts was
9/1, which exceeds the azeotropic distillation composition
of 8/2. The distillation was conducted over 1.5 hours under
the above conditions and as a result 900 g of distillates
was obtained in a dry ice-acetone cooling bath. At this
time the EVOH in the bottoms had a saponification degree of
99.8~.
-53-
~167~3
.
During the above reaction and the further saponifica-
tlon reaction the reaction zone maintained always a
homogeneous state. To the bottoms after the further saponi-
fications 2.37 g (0.0395 mole) of acetic acid was added to
deactivate the catalyst. The concentration of EVOH in the
bottoms was adjusted while the bottoms temperature was
maintained at not higher than 90~C under reduced pressure,
to obtain a 17% solution of EVOH solution in DMSO.
The EVOH solution thus obtained was, as a spinning
dope, fed to a dry-jet-wet spinning apparatus and extruded
through a spinneret at a spinning head temperature of 80~C
into a coagulating bath of MeOH/DMSO = 7/3 (by weight) at a
bath temperature of 5~C. The extruded fiber was subjected
to the succeeding treatment steps of removal by extraction
with MeOH of remaining DMSO, wet heat drawing, drying and
dry heat drawing, to give an EVOH fiber. The fiber had a
strength and elongation of 15.2 g/d and 4.5% respectively
and a hot water resistance of 130~C as expressed by
temperature of water in which the fiber under a constant
load (200 mg/d) breaks.
Example 3-2
Example 3-1 was repeated except for using as EVA 317 g
(3.95 moles) of one having an ethylene content of 10 mol%
and an [~ ]inh of 0.271 l/g to obtain a 7% solution in DMSO
of an EVOH having a saponification degree of 99.7%. All
through the procedures of saponification, further
saponification, deactivation of catalyst and adjustment of
-54-
21~79~
concentration, the reaction system maintained a homogeneous
state. The solution thus obtained was casted onto a poly-
ethylene terephthalate film and the film was immersed in a
MeOH coagulating bath- at 10~C to form the solution into
film. The film was introduced in MeO~ extraction bath,
where DMSO was removed by extraction. The film was then air-
dried at room temperature, stretched in one direction at
150-C by 6 times and further heat fixed under constant
length in an atmosphere of nitrogen gas at 190~C for 3
minutes, to give an EVOH film having a thickness of 24 ~m
containing almost no gels or irregular matter.
Example 3-3
Example 3-1 was repeated except for using-as EVA 266 g
(3.95 moles) of one having an ethylene content of 32 mol~
and an ~ ]inh of 0.106 l/g and 7.9 g (0.198 mole) of sodium
hydroxide as a saponification catalyst, to obtain a 25%
solution in DMSO of an EVOH having a saponification degree
of 99.5%. All through the procedures of saponification,
further saponification, deactivation of catalyst and adjust-
ment of concentration, the reaction system maintained a
homogeneous state. The solution thus obtained was heated to
a temperature of 70~C and then extruded through a slit of a
sheet f orming machine into a cooling water kept at a tempe-
rature of 3~C, coagulated therein, to form a white opaque
sheet-shaped wet gel having a thickness of 600 ~m. The gel
thus obtained was immersed in water at 65~C for 3 minutes
and dried at 40~C for 60 minutes, to give a sheet having a
-55-
~ 73~ 3
thic~ness of 480 ~m.
Example 3-4
- Example 3-1 was repeated except for using 1,021 g (22.2
moles) of ethanol instead of MeOH, 1,700 g of diethyl sulf-
oxide instead of DMSO and 4.43 g (0.079 mole) of potassium
hydroxide instead of sodium hydroxide, to obtain a 15% solu-
tion in diethyl sulfoxide of an EVOH having a saponification
degree of 99.6%. All through the procedures of saponifica-
tion, further saponification, deactivation of catalyst and
. - .
adjustment of concentration, the reaction system maintained
a homogeneous state. The solution thus obtained was, as a
spinning dope, fed to a spinning apparatus of wet flow-up
system and extruded through a spinneret at a head tempera-
ture of 60~C into a coagulating bath of ethanol/diethyl
sulfoxide of 4/1 by weight at a bath temperature of 5~C.
The extruded fiber was then subjected to the succeeding
steps of removal by extraction with ethanol of diethyl
sulfoxide, wet heat drawing, drying and dry heat drawing, to
give an EVOH fiber. The fiber had a strength and e.longation
of 14.9 g/d and 4.8%, respectively.
Example 3-5
Example 3-1 was repeated except for using as EVA 261 g
(3.90 moles) of one having an ethylene content of 33 mol%
and an [~ ]inh o~ 0.148 l/g and 7.9 g t0.198 mole) of sodium
hydroxide as a saponification catalyst, to obtain a 13%
solution in DMSO of an EVOH having a saponification degree
of 99.8~. All through the procedures of saponification,
. _5~_ .
~7~3
.
further saponification, deactivation of catalyst by equimol-
ar addition of acetic acid and adjustment of concentration,
the reaction system maintained a homogeneous state and no
deposit of gels or -the like on the reactor wall was
observed. The solution thus obtained was, as spinning dope,
extruded through a ring nozzle of a wet hollow-fiber
manufacturing apparatus with an inside injection agent of
nitrogen into a coagulating bath of 30% by weight aqueous
DMSO solution kept at -7~C and at a nozzle draft of 1.5, to
give an EVOH hollow fiber. The fiber was then wet heat-
treated at 40~C for 6 minutes, washed with water and then
with acetone and dried, to give a finished follow fiber
having a water permeability of 6 ml/mmHg hr/m2.
Example 3-6
15. Example 3-1 was repeated except for using as EVA 174 g
(4.0 moles) of one having an ethylene content of 70 mol% and
an [~ ]inh of 0.078 l/g, 384 g (12.0 moles) of MeOH and
1,700 g of DMSO and 16 g (0.4 mole) of sodium hydroxide as a
saponification catalyst, and repeating further saponifica-
tion by addition of 256 g (8.0 moles) of MeOH after having
distilled off methyl acetate/MeOH by the first further
saponification, to obtain a 12% solution of an EVOH having a
saponification degree of 99.5~ in DMSO. All through the
procedures of methanolysis, first and second further saponi-
fication, deactivation of catalyst by equimolar addition of
acetic acid and adjustment of concentration, the reaction
system maintained a homogeneous state and no deposit of gels
~16~3
-
or the like was observed. The solution of EVOH thus
obtained was fed to a pulverizing apparatus provided with a
vibration nozzle having a diameter of 0.6 mm and pulverized
therein with a coagulating bath of water at 20~C under
vibration at 70 Herz into spherical gels having an average
particle diameter of 1.5 mm. The spherical gels were then
washed with water and dried to give a spherical polymer
having an average particle diameter of 0.55 mm and an
average ratio of maximum width/maximum length of 0.9 and
having a sharp particle size distribution.
Comparative Example 3-1
- An attempt was made to conduct methanolysis in the same
manner as in Example 3-1, with 344 g (4.0 moles) of a
polyvinyl acetate having an [~ ]inh of 0.186 l/g instead of
EVA and 2,400 g of MeOH but without addition of DMSO. Just
after the start of methanolysis, the reaction system became
heterogeneous so that reaction in a homogeneous state was
impossible.
Comparative Example 3-2
An attempt was made to conduct methanolysis in the same
manner as in Example 3-1, using as EVA 135 g (4.0 moles) of
one having an ethylene content of 90 mol~ and an [~ ]inh of
0.0678 l/g. The copolymer dissolved in the reaction zone
only insufficiently. Methanolysis was conducted with the
heterogeneous state as it is for 2 hours. The reaction
system remained heterogeneous. The polymer obtained after
the reaction showed a saponification degree of only 52~.
-58-
. . 21~79i~3
Example 4-1
A 5-liter autoclave equipped with a electromagnetic
stirrer and a sampling port was charged with 2.74 kg (31.86
moles) of vinyl acetate (VAc), 0.69 kg of DMSO (VAc/DMSO =
4/1 by weight) and 0.159 g of azobisisobutyronitrile
(0.0058% by weight based on the weight of VAc). The inside
atmosphere was thoroughly replaced with ethylene gas and the
contents were pressurized by a pressure adjusting apparatus
to an ethylene pressure of 3 kg/cm2. With the ethylene
pressure being maintained at this level, the temperature was
elevated up to 60~C and copolymerization of ethylene and
vinyl acetate was started under the constant temperature
condition of 60~C. The polymerization was allowed to
proceed for 5 hours, while the reaction process was being
monitored by sampling. The polymerization system remained
homogeneous solution over all the reaction period and
conversion after 5 hours was 30%.
The EVA sampled from the solution showed an ethylene
content of 5 mol% and an ~ ]inh as measured on EVOH after
saponification of 0.247 l/g. To the polymerization solution
a polymerization inhibitor was added and the mixture was
introduced into a 10-liter separable flask equipped with a
stirrer, a reduced-pressure distillation apparatus, a cata-
lyst liquid inlet and a sampling port under an atmosphere of
nitrogen. Thereafter, 3,700 g of DMSO was added and the
inside temperature was elevated with an oil bath and with
stirring up to 60~C. Distilling off of residual VAc was
-59-
g 5 3
-
conducted under the constant bottoms temperature condition
of 60~C while the degree of reduced pressure was gradually
changed (50 mmHg to 5 mmHg). The solution had a viscosity
of 11 poises just after start of the distilling off and that
of 19 poises when finished. By collecting of 2 kg of the
distillate, it was confirmed that the residual VAc in the
bottoms had become 0.02~. This operation of distilling off
was able to be conducted in the state of a homogeneous solu-
tion. Next, to the bottoms maintained at a temperature of
60~C, 1,700 g (53.13 moles) of MeOH, and to the mixture a
catalyst solution of 3.82 g (0.096 mole) of sodium hydroxide
in 100 ml of MeOH was added at once under an atmosphere of
nitrogen, to start reaction, which continued at 60~C over 30
minutes. The EVOH sampled after the 30 minutes' reaction
had a saponification degree of 97.8~. A reduced-pressure
distillation apparatus was attached to the above reactor and
further saponification of EVOH was conducted at a constant
bottoms temperature of 70~C while byproduced methyl acetate
and MeOH were being distilled off under normal or reduced
pressure. The ratio by weight of methyl acetate/MeOH in the
distillate just after the start of the distillation was 9/1,
which exceeded the azeotropic distillation composition of
methyl acetate/MeOH of 8/2. The distilling off was
conducted over 1.5 hours under the above condition, whereby
2,250 g of distillate was collected in a dry ice-acetone
cooling bath. The EVOH in the bottoms had a saponlfication
degree of 99.8~.
-60-
21679~3
During the above reaction and the further saponifica-
tion reaction the reaction zone always maintained a
homogeneous state. To the bottoms a~ter the further saponi-
fication, 5.76 g (0.096 mole) of acetic acid was added to
deactivate the catalyst. The concentration of EVOH in the
bottoms was adjusted while the bottoms temperature was main-
tained at not higher than 90~C under reduced pressure, to
obtain a 12% by weight solution of EVOH solution in DMSO.
The EVOH solution thus obtained was, as a spinning
dope, fed to a dry-~et-wet spinning apparatus and extruded
through a spinneret at a spinning head temperature of 80~C
into a coagulating bath of MeOH/DMSO = 7/3 (by weight) at a
bath temperature of 5~C. The extruded fiber was subjected
to the succeeding treatment steps of removal by extraction
with MeOH of remaining DMSO, wet heat drawing, drying and
dry heat drawing, to give an EVOH fiber. The~ fiber had a
strength and elongation of 16.5 g/d and 4.7% respectively
and a hot water resistance of 135~C as expressed by tempe-
rature of water in which the fiber under a constant load
(200 mg/d) breaks.
Example 4-2
Example 4-1 was repeated except for changing the amount
of azobisisobutyronitrile added to the polymerization zone
to 0.225 g (0.0082~ by weight based on the weight of VAc)
and using an ethylene pressure of 7 kg/cm2, to obtain in a
conversion of 31~ an EVA having an ethylene content of 10
mol~ and an [~ ]inh as measured on the corresponding EVOH of
-61-
~157~ 3
0.210 l/g. The residual VAc was distilled off from the
solution in the same manner as in Example 4-1 and final
residual VAc amount was confirmed to be not more than 0.02~.
The solution had a viscosity of 9 poises just after the-
start of the distilling off, and that of 15 poises when it
finished. All through the above procedure the system always
maintained a homogeneous state. Saponification, further
saponification and adjustment of solution concentration were
conducted in the same manner as in Example 4-1, to obtain a
6~ by weight solution in DMSO of an EVOH having a
saponification degree of 99.7~.
All through the above procedure, the reaction system
maintained a homogeneous state. The solution thus obtained
was casted onto a polyethylene terephthalate film and the
film was immersed in a MeOH coagulating bath at 10~C to form
the solution into film. The film was introduced in MeOH
extraction bath, where DMSO was removed by extraction. The
film was then air-dried at room temperature, stretched
monoaxially at 150~C by 6 times and further heat fixed under
constant length in an atmosphere of nitrogen gas at 190~C
for 3 minutes, to give an EVOH film having a thickness of 20
~m containing almost no gels or irregular matter.
Example 4-3
Example 4-1 was repeated except for changing the amount
of azobisisobutyronitrile to the polymerization zone to 1.10
g (0.04~ by weight based on the weight-of VAc) and using an
ethylene pressure of 43 kg/cm2, to obtain in a conversion of
-62-
CA 021679~3 1998-10-22
30~ a solution of an EVA having an ethylene content of 32 mol~
and an [~] inh as measured on the corresponding EVOH of
0.119 l/g. The residual VAc was distilled off from the
solution in the same manner as in Example 4-1 and final
residual VAc amount was confirmed to be not more than 0.02~.
The solution had a viscosity of 5 poises just after the start
of the distilling off, and that of 7 poises when it finished.
All through the above procedure the system always
maintained a homogenous state. Saponification with 19.1 g
(0.48 mole) of sodium hydroxide as a saponification catalyst,
further saponification and adjustment of solution
concentration were conducted in the same manner as in
Example 4-1, to obtain a 21~ solution in DMSO of an EVOH
having a saponification degree of 99.5~. All through the
above procedures, the reaction system maintained a homogenous
state.
The solution thus obtained was heated to a temperature of
70~C and then extruded through a slit of a sheet forming
machine into a cooling water kept at a temperature of 3~C,
coagulated therein, to form a white opaque sheet-shaped wet
gel having a thickness of 600 ~m. The gel thus obtained was
immersed in water at 65~C for 3 minutes and dried at 40~C
for 60 minutes, to give a sheet having a thickness of
450 ~m.
Example 4-4
The procedures of copolymerization, distilling off of
- 63 -
residual VAc, saponification and further saponification were
conducted in the same manner as in Example 4-1 and adjust-
ment of solution concentration was so conducted as to obtain
a 10% solution in DMSO of an EVOH having a saponification
degree of 99.8%. The solution thus obtained was, as a spin-
ning dope, fed to a spinning apparatus of wet flow-up system
and extruded through a spinneret at a head temperature of
60~C into a coagulating bath of MeOH/DMSO of 4/1 by weight
at a bath temperature of 5~C. The extruded fiber was then
subjected to the succeeding steps of removal by extraction
with MeOH of DMSO, wet heat drawing, drying and dry heat
drawing, to give an EVOH fiber. The fiber had a strength
and elongation of 16.2 g/d and 4.9%, respectively.
-64-
~1~7g~3
Example 4-5
Example 4-1 was repeated except for changing the amount
of azobisisobutyronitrile to the polymerization zone to 2.33
g (0.085% by weight based on the weight of VAc) and using an
ethylene pressure of 32 kg/cmZ, to obtain in a conversion of
20% a solution of an EVA having an ethylene content of 32
mol~ and an ~ ]inh as measured on the corresponding EVOH of
0.143 l/g. The residual VAc was distilled off from the
solution in the same manner as in Example 4-1 and final
~0 residual VAc amount was confirmed to be not more than 0.02%.
All through the above procedures, the reaction system
maintained a homogeneous state. Saponification with 26.9 g
(0.67 mole) of sodium hydroxide as a saponification
catalyst, further saponification and adjustment of solution
concentration were conducted in the same manner as in
Example 4-1, to obtain a 12% solution in DMSO of an EVOH
having a saponification degree of 99.6%. All through the
above procedures, the reaction system maintained a
homogeneous state and no deposit of gels or the like on the
reactor wall was observed.
The solution thus obtained was, as spinning dope,
extruded through a ring nozzle of a wet hollow-fiber
manufacturing apparatus with an inside injection agent of
nitrogen into a coagulating bath of 30% by weight aqueous
DMSO solution kept at -7~C and at a nozzle draft of 1.5, to
give an EVOH hollow fiber. The fiber was then wet heat-
treated at 40~C for 6 minutes, washed with water and then
-65-
~ J~
._
with acetone and dried, to give a finished follow fiber
having a water permeability of 6.3 ml/mmHg hr/m2.
Example 4-6
Example 4-1 was repeated except for using 1,800 g
(20.93 moles) of vinyl acetate, 1,200 g of DMSO (VAc/DMSO =
6/4 by weight) and 2.36 g (0.131% by weight based on the
weight of VAc) of azobisisobutyronitrile and using an
ethylene pressure of 65 kg/cm2, to obtain in a conversion of
30~ a solution of an EVA having an ethylene content of 60
mol% and an [~ ]inh as measured on the corresponding EVOH of
0.085 l/g. The polymerization zone always maintained a
homogeneous state. The residual VAc was distilled off from
the solution while 4,800 g of DMSO was added, in the same
manner as in Example 4-1, during which the reaction system
maintained a homogeneous state.
Saponification was conducted by addition of 1,500 g
(47.1 moles) of MeOH and 31.4 g (0.79 mole) of sodium
hydroxide, and further saponification was conducted to
distill off methyl acetate/MeOH. Thereafter, once again
further saponification was conducted by addition of 973 g
(30.4 moles) of MeOH. Then, deactivation of catalyst by
addition of acetic acid in an amount of the same moles as
that of the sodium hydroxide fed and adjustment of solution
concentration were conducted in the same manner as in
Example 4-1, to obtain a 11.5~ solution in DMSO of an EVOH
having a saponification degree of 99.6%. All through the
above procedures, the reaction system maintained a
-66-
~1~79~3
homogeneous state. The solution o~ the EVOH was fed to a
pulverizing apparatus provided with a vibration nozzle
having a diameter of 0.6 mm and pulverized therein with a
coagulating bath of water at 20~C under vibration at 65 Herz
into spherical gels having an average particle diameter of
1.5 mm. The spherical gels were then washed with water and
dried to give a spherical polymer having an average particle
diameter of 0.55 mm and an average ratio of maximum
width/maximum length of 0.9 and having a sharp particle size
distribution.
Comparative Example 4-1
Example 4-1 was repeated except for using instead of
DMSO 0.69 kg of MeOH (VAc/MeOH = 4/1 by weight) and 0.39 g
(0.014% by weight based on the weight of VAc) of
azobisisobutyronitrile and without ethylene, to conduct
homopolymerization of vinyl acetate for 5 hours. The con-
version was 50% and the obtained polymer showed an [~ ]inh
of 0.210 l/g as measured on the corresponding polyvinyl
alcohol. Remaining VAc was distilled by adding ~.5 kg of
MeOH instead of DMSO and under normal pressure, to obtain a
35~ by weight solution of polyvinyl acetate in MeOH. All
through the above procedures, the system showed a homogene-
ous state. Saponification was started under the same
conditions as in Example 4-1 by adding 6.4 g (0.16 mole) o~
sodium hydroxide to the above solution of polyvinyl acetate
in MeOH. Just after the start of the saponification, the
reaction system became heterogeneous and the reaction in a
~1~7~-3
homogeneous state was impossible.
Comparative Example 4-2
Example 4-1 was repeated except for using instead of
DMSO 0.69 kg of MeOH (VAc/MeOH = 4/1 by weight) and 3.23 g
of azobisisobutyronitrile (0.118% by weight based on the
weight of VAc) and using an ethylene pressure of 62.5 kg/cm2
and a polymerization temperature of 50~C, to conduct
polymerization. Samples taken from the polymerization were
opaque and the system was observed to be in a heterogeneous
state. The conversion after 6 hours was 30% and the obtain-
ed polymer had an ethylene content of 60 mol% and an [~ ]inh
of 0.0749 l/g as measured on the corresponding EVOH.
Remaining VAc was distilled by adding to the thus obtained
solution 3.0 kg of MeOH instead of DMSO and under normal
pressure in the same manner as in Example 4-1. The bottoms
became more turbid as VAc was being distilled off and there
was observed precipitates of EVA, so that it was difficult
to distill off VAc in a homogeneous state.
Examples 5-1 through 5-4
EVA's having an ethylene content of 0 (PVAc), 20, 32,
47 and 60 mol~, respectively, were subjected, in the same
manner as in Example 2-1 , under conditions as shown in Table 4
and at 40~ C for 60 minutes. The polymers were each
precipitated by adding a solvent appropriately selected,
depending on the ethylene content and saponification of the
polymer, from water, MeOH or mixed solvent of the two.
After the reaction, the solutions were all homogenous.
-68-
~ ~7g53
._
FIGURE 4 shows the change of the saponification degree
with time.
- As control, Example 5-1 was repeated except for using
MeOH instead of DMSO, to conduct saponification. The
polymers obtained after the reaction were pulverized, neu-
tralized and then subjected to after-treatment (Comparative
Examples 5-1 through 5-5).
With the MeOH system, the reaction mixtures were solid
or slurry, differing depending on the ethylene content
though.
FIGURE 5 shows the change of the saponification degree
with time in these MeOH systems.
As is apparent from comparison of FIGURE 4 with FIGURE
5, with DMSO solvent system the reaction proceeds much
faster than with MeOH system.
The rate of reaction corresponding to each of the eth-
ylene contents and with each solvent system was calculated
from FUGURES 4 and 5, and the ratio of the rate with DMSO-
saponification system to that with MeOH-saponification
system was obtained (FIGURE 6). As understood from FIGURE
6, the rate ratio increases with increasing ethylene
content, which means that the saponification reaction with
DMSO is very specific.
Examples 6-1 through 6-5
Polymerization was conducted in a manner similar to
that in Example 1 by feeding the same amounts of DMSO and
vinyl acetate (DMSO/VAc = 5/5 by weight) and varying the
-69-
~1~7g~3
-
ethylene pressure, while the amount of the initiator was so
adjusted as to realize the same polymerization rate and
conversion. The EVA's obtained were saponified in the same
manner as in Example 1 and the obtained EVOH's (saponifica-
tion degree: 99.4 to 99.7%) were tested for inherent
viscosity.
As control, polymerization was conducted in MeOH
systems without DMSO and in the same compositions as in the
above DMSO system (Comparative Examples 6-1 through 6-5).
Here, the ethylene pressure for each reaction was set such
that the same polymerization rate, conversion and ethylene
content would be realized (Table 5 and FIGURE 7). As seen
from FIGURE 7, EVOH's obtained by solution polymerization
with DMSO solvent have higher inherent viscosity than those
obtained with MeOH solvent system.
Example 7-1
The procedure of Example 3-1 was followed with 100 g of
EVA having an ethylene content of 32 mol~ and [~ ]inh of
0.111 l/g, 96 g of MeOH and 1,788 g of DMSO and using 2.0 g
of sodium hydroxide as saponification catalyst, to effect
reaction at 40~C for 2 minutes. Then the same after-treat-
ment as in Example 3-1 was conducted to obtain a partially
saponified EVOH having a saponification degree of 76.5%, a
melting point of 116.4~C and a block character of 0.345.
As control (Comparative Example 7-1), Example 7-l was
repeated except for using MeOH instead of DMSO, to effect
reaction at 40~C for 90 minutes, followed by same after-
- -70-
~16~9~ ~
treatment, to obtain a partially saponified EVOH having a
saponification degree of 76.5%, melting point of 143.8-C and
a block character of 0.118.
The above facts show that saponification in DMSO
solvent gives EVOH with the same saponification degree but
having lower melting point than that obtained with MeOH
solvent, and that the former (DMSO-saponification system)
has sharper distribution of remaining acetyl groups, i.e.
more randomized distribution, than the latter (MeOH-
saponification system).
As stated heretofore, the processes of the presentinvention produce the following effects.
Ethylene-vinyl ester copolymers having a wide range of
ethylene content can be obtained. Since the polymerization
zone is maintained in a substantially homogeneous liquid
phase, the resulting EVA and further EVOH obtainable there-
from both have uniform properties and residual monomer can
readily be recovered. Furthermore, there can be obtained
EVA with higher polymerization degree than that with
Z0 solution polymerization using MeOH.
Obviously, numerous modifications and variations of the
invention are possible in light of the above teachings. It
is therefore understood that within the scope of the
appended claims, the invention may be practiced otherwise
than as specifically described herein.
-71-
.
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-76-
