Note: Descriptions are shown in the official language in which they were submitted.
7047
PS-t
~3~B~3~
1 IMPROVED PROCESS FOR PREPARING INTERPOLYMERS
OF ETHYLENE, VINYL ACETATE, AND REACT~VE
HALOGEN-CONTAINING MONOMERS
This invention relates to an improved proces~
for the preparation of high Mooney viscosity inter-
polymer elastomers of ethylene, vinyl acetate and
reactive halogen-containing monomers, such as vinyl
chloroacetate (VCA). The incorporated halogen-
containing units serve as cure sites for vulcanization.
More particularly, the process is directed to novel
methods for introducing the vinyl chloroacetate curesite monomer during polymerization so that inter-
polymer elastomer products which exhibit increased
tensile strength properties upon vulcanization are
obtained.
The production of ethylene-vinyl acetate-
vinyl chloroacetate (E/VA/VCA) interpolymer elastomers
is known in the art. For example, Kaizerman, et
al., in U.S. Patent No. 3,972,857, prepare
E/VA/VCA interpolymers by chemically reacting an
ethylene-vinyl acetate (EVA) copolymer elastomer
with chloroacetic acid in xylene solution using
p-toluenesulfonic acid as the catalyst. Acetic
acid produced by acidolysis of the EVA
copolymer by the chloroacetic acid, is removed
by distillation and the EVA copolymer, now
3o
I _
~3~
1 containing chemically-introduced VCA units, is
obtained by precipitation with isopropyl
alcohol. Elastomers containing from 0.2 to 4.5
- weight percent chlorine which can be vulcanized
with soap/sulfur cure systems are obtained.
Another method of producing
soap/sul~ur vulcanizable ethylene-vinyl acetate
elastomer compositions is that of Chang e~ al.
in U.S. Patent No. 4,202,845. Chang et al.
graft an acrylate ester monomer along with a
vinyl chloroacetate cure site monomer onto an
elastomeric EVA copolymer backbone.
As indicated, both o~ the above
compositions which contain reactive halogen cure
sites undergo soap/s~tlfur vulcanization to
obtain useful elastomeric products. Typically,
soap/sulfur w lcanization involves, in addition
to elastomer and carbon black reinforcing agent,
a soap such as sodium stearate or sodium
2-ethylhexanoate, sulfur, stearic acid and an
antio~idant. No unsaturation is required in the
elastomer for soap/sulfur vulcanization. While
the exact mechanism is uncertain, there are
indications that -Sx- crosslinks are introduced
~Kaendler et al.~ Die Angewandte Makromolekulare
Chemie, 29~30, 241(1973)~. In any event,
soap/sulfur vulcanization differs fundamentally
from conventional sulfur vulcanization where
carbon-carbon double bond unsaturation must be
present in the elastomer.
There are several disadvantages
associated with the aforesaid chemical processes
~3~
1 of Kaizerman et al. and Chang et al. for
- introducing cure sites into ethylene~vinyl
acetate copolymer elastomers. First of all for
Kaizerman et al., a multi-step procedure is
involved which increases costs. The EVA first
has to be synthesized, then dissolved in xylene,
and thereafter reacted with chloroacetic acid in
a relatively slow, complicated solvent process.
The chemically modified product must then be
recovered by precipitation with a nonsolvent,
such as isopropyl alcohol, and dried. ~ecovery,
separation and purification of solvent and
non-solvent are required for commercial
operation.
15 - The Chang et al. graft polymerization
is also a multi-step process and suffers from
the attendant increases in cost. The EVA
elastomer must first be synthesized and then
grafted in a slurry process with a substantial
amount of relatively expensive acrylate ester
monomer, said graft process also incorporating
the VCA cure sites into the finished graft
composition.
It would be highly desirable and
advantageous if a simple, low cost procedure for
interpolymerizing ethylene and vinyl acetate
with a comparatively small amount of VCA or
other similar halogen-containing cure site
monomer were available. It is, however,
recognized among polymer chemists that VCA is a
rather potent chain transer agent. This
propensity to chain transfer tends to limit the
~3VU8
1 molecular weight of the interpolymers that can
- be produced using VCA as the cure site monomer.
The aforesaid chain transfer charac~er of the
cure site monomer becomes even more o~ a problem
at higher temperatures such as are employed for
conventional high pressure polymerization
processes. Thus, in order to produce
sufficiently high molecular weight E/VA/VCA
interpolymer elastomers, the polymerizations
have typically been conducted at relatively low
temperatures by redo~-initiated polymerization
in aqueous emulsion or solution.
One such method for the emulsion
polymerization of ethylene, vinyl acetate and
vinyl chloroacetate is disclosed by Becker et
al. in U.S. Patent No. 4, 098,746. Becker et al.
disclose that the polymerization may be carried
out in a batch process or by feeding the
monomers to the reaction medium. They also
indicate the polymerization can be carried out
at a constant, increasing, or decreasing
ethylene pressure. There is, however, no
disclosure by Becker et al. of what effect the
manner or rate o~ varying ethylene pressure or
monomer addition during the interpolymerization
process might have on the properties o the
interpolymer. Moreover, when Becker et al. add
VCA monomer during the course of the
polymerization, it is introduced as a dilute
solution (up to about 10 weight percent) in
vinyl acetate monomer, as such or as an aqueous
emulsion. Addition of VCA monomer alone or at
~L3UO~
1 relatively high concentrations in vinyl acetate
- monomer is not suggested by Becker et al.
Furthermore, Becker et al. do not employ
soap/sulfur cure systems but rather utilize
cross-linking agents, such as aminoplast resins,
polyamines, polyamidoamines, or mixtures of
formaldehyde and ammonia or amine, for
cross-linking.
Heimberg in U.S. 4,287,329 discloses
an emulsion polymerization process for
synthesizing EVA elastomers of low gel content
containing about 40% to about 70~ by weight of
vinyl acetate and having Mooney viscosities of
about 30 to 80. In contrast to EV~ elastomers
the art produced by high pressure
polymerization processes conducted at relatively
high temperatures and which seldom have Mooney
viscosities much in excess of about 20 and as a
result are soft and tacky and very difficult to
handle and compound on rubber processing
equipment, the high Mooney viscosity emulsion
elastomers of Heimberg are less tacky and
present much less difficulty in handling and
compounding on the rubber mill.
We have now quite unexpectedly
discovered an improved process whereby high
Mooney viscosity interpolymers of vinyl acetate J
ethylene, and reactive halogen-containing cure
site monomers are readily produced. More
3 specifically, the present invention is directed
1 to a process wherein ethylene, vinyl acetate,
and a halogen-containing monomer, such as vinyl
chloroacetate, are polymerized to produce
- improved interpolymers, namely, high Mooney
viscosity interpolymer elastomers which upon
soap/sulfur vulcanization have increased tensile
strengths. In one embodiment of the invention,
the cure site monomer is introduced
incrementally or continuously during the course
of the polymerization process instead of at the
start of the polymerization. In another
embodiment, the halogen-containing cure site
monomer is added to the polymerization neat or
diluted wi~h the vinyl acetate monomer at a
concentration of at least 20 weight percent. In
yet another embodiment, the ethylene pressure is
also increased throughout the course of the
polymerization.
More specifically, the process relates
to the interpolymerization of ethylene, vinyl
acetate, and a halogen-containing cure site
monomer in an aqueous emulsion containing a
nonionic surface active agent, an anionic
surface active agent, and a free radical
polymerization catalyst to obtain a soap/sulfur
vulcanizable elastomer containing from 40 to 70
weight percent vinyl acetate and 0.2 to 2 weight
percent chlorine, by conducting the polymerization
at a temperature from 5C to 80c and, more
3o preferably, from ~0 toS5c and ethylene
pressure of ~0~4~00-psi~i and adding the
. .
~3U~
1 halogen-containing monomer after the
polymerization is initiated, said addition being
made continuously or intermittently over at
~ least one-twentieth of the total polymerization
period. In another embodiment of the invention,
a process is provided wherein the improvement
comprises conducting the polymerization at a
temperature from 5C to 80C and, more
preferably, from 20C to 55C and adding the
halogen~containing monomer after the
polymerization is initiated continuously or
intermittently over at least one-twentieth of
the total polymerization period, and increasing
the ethylene pressure during the polymerization
from 400-900 psig at the outset up to 2000-4000
psig by the end of the polymerization period.
The halogen-containing cure site monomer is
preferably vinyl chloroacetate which can be
added to the polymerization neat, i.e., by
itself, or in solution diluted with the vinyl
acetate monomer. Where a solution of vinyl
chloroacetate and vinyl acetate is employed, the
concentration of the halogen-containing cure
site monomer in vinyl acetate is at least 20
weight percent. No more than about one-half of
the total vinyl acetate monomer charge is
employed for this purpose--the remainder of the
vinyl acetate monomer being charged to the
reactor prior to initiation of the
polymerization. When the vinyl chloroacetate is
charged to the polymerization neat, it is
preferred that all of the vinyl acetate monomer
~L3U~
1 is present in the reactor when the
polymerization is initiated although it is
possible to add up to about one-half of the
vinyl acetate as a separate stream during the
course of the polymerization.
DETAII.ED_DESCRIPTION OF THE INVENTION
The terpolymers of this invention can
have either ethvlene or vinyl acetate as the
predominant monomer. When utilizing vinyl
chloroacetate as the halogen-containing cure
site monomer, the compositions will be re~erred
to as ethylene-vinyl acetate-vinyl chloroacetate
(E/VA/VCA) interpolymers. If vinyl acetate is
the predominant monomer the interpolymers are
sometimes referred to as vinyl
acetate-ethylene-vinyl chloroacetate (VA/E/VCA)
interpolymers.
Generally, the interpolymers have from
about 40 to about 70 weight percent and, more
preferably, from about 55 to about 65 weigh~
percent vinyl acetate incorporated therein.
They generally contain from about 0.2 to about 2
weight percent chlorine. More commonly, the
chlorine content is 0.5 to 1 weight percent.
When the halogen-containing cure site monomer is
VCA, these chlorine content ranges correspond to
0~68 to 6.8 and 1.7 to 3.4 weight percent
incorporated VCA, respectively. The balance of
the interpolymer composition consists o~
incorporated ethylene units and units o~ any
other ethylenically unsa~urated monomers which
\ `\ 9
1 are included in the polymerization. Ethylene
generally constitutes from about 25 to 60 weight
percent and, more preferably, from about 30 to
45 weight percent of the elastomer.
Reactive halogen-containing monomers
which can be utilized as cure site monomers are
vinyl monomers selected from the group
consisting of vinyl chloroacetate, vinyl
bromoacetate, vinyl 2-chloropropionate, vinyl
2-chlorobutyrate, vinyl 2-chloroisobutyrate, and
2-chloroethyl vinyl ether. Glycidyl acrylate
and glycidyl methacrylate may also be employed
as the reactive monomer as can other
halogen-containing monomers such as allyl
chloroacetate, vinyl 3-chloropropionate, vinyl
4-chlorobutyrate, haloacrylate esters, such as
2-chloroethyl methacrylate, vinylbenzyl
chloride, and the like. Vinyl chloroacetate is
a particularly use~ul cure site monomer for the
process of the invention.
Other ethylenically unsaturated
monomers may also be included with the ethylene,
vinyl acetate and halogen-containing cure site
monomer. If employed, these monomers are
present in amounts typically not exceeding about
10 weight percent of the total interpolymer
elastomer. Included among such additional
comonomers are monoethylenically unsaturated
aliphatic hydrocarbons such as propylene and
isobutylene; halogen-containing ole~inic
monomers such as vinyl fluoride, vinyl chloride,
vinyl bromide, vinyliden~ di~luoride,
3~
:~L3~ 0~
l-chloro-l-fluoro-ethylene,
- chlorotrifluoroethylene and tetrafluoroethylene;
unsaturated monocarboY~ylic acid monomers such as
acrylic acid, me~hacrylic acid, and crotonic
acid, as well as polymerizable derivatives
thereof, e.g., alkyl acrylates and methacrylates
such as methyl acrylate, ethyl acrylate,
n-propyl acrylate, n-butyl acrylate, isobutyl
acrylate, 2-ethylhexyl acrylate, methyl
methacrylate, ethyl methacrylate, n-propyl
methacrylate, isobutyl methacrylate,
1,6-he~anediol diacrylate, acrylonitrile,
methacrylonitrile, acrylamide, methacrylamide,
N-methylolacrylamide, N-methoxymethylacrylamide
and N~butoxymethylacrylamide, and acrolein;
alkyl esters of monoethylenically unsaturated
dicarboxylic acids, e.g., diethyl maleate,
dibutyl maleate, dioctyl maleate, dipropyl
fumarate, dibutyl fumarate, dioctyl ~umarate,
didodecyl fumarate, dibutyl itaconate and
dioctyl itaconate; aliphatic vinyl esters such
as vinyl formate, vinyl propionate, vinyl
trimethylacetate, and vinyl butyrate; aliphatic
vinyl ethers such as methyl vinyl ether, ethyl
vinyl ether and n-butyl vinyl ether; vinyl
ketones such as methyl vinyl ketone, ethyl vinyl
ketone, and butyl vinyl ketone.
The polymerization may be carried out
as a batch process or a continuous process. It
may be performed in bulk, without solvent, with
only monomers and auxiliary adjuvants such as
initiators present to promote the polymerization
~3~:?B~l
11
1 process or it may be performed in solution in a
suitable solvent, e.g., methanol, t-butyl
alcohol, toluene, etc. Preferably, it is
- carried out as an emulsion polymerization
process in an aqueous medium.
The process is most generally carried
out as a batch emulsion polymerization process
but it is within the scope of this invention to
carry out the process in a series or "cascade"
of successive batch reactors ~Iherein the
polymerizing system is pumped from one reactor
to the next, as the polymerization reaction
progresses, and in that manner approaches a
continuous process.
When the interpolymerization process
of this invention is carried out in aqueous
emulsion, a nonionic and anionic surfactant, a
catalyst, a buffer, ferrous sulfate heptahydrate
and a reducing agent are included with the water
and monomers. Generally, the surfactants,
catalyst, buffer, and ferrous sulfate
heptahydrate are dissolved in deionized water
and added directly to the reactor before
starting the polymerization. The vinyl acetate
monomer is then added although, if desired, it
may be added in part d~ring the polymerization.
Most generally, the major portion (more than
one-half) of the vinyl acetate is added to the
reactor be~ore polymerization is commenced. The
initial ratio of water to vinyl acetate monomer
in the polymerization can range fro~ about 40
parts to about 1700 parts per 100 parts of vinyl
~3~
12
l acetate monomer with a ratio of about 75 to
- about 120 parts of water per 100 parts of vinyl
acetate monomer being preferred. After the
vinyl acetate monomer has been added, the
reactor is closed, the stirrer is started, and
air is displaced from the interior of the
reactor and lines leading to it by alternately
imposing and releasing nitrogen pressure.
Thereafter, ethylene pressure is applied to the
reactor and the contents thereof are stirred and
heated to the desired polymerization
temperature. The ethylene pressure is adjusted
to that selected for the polymerization and the
polymerization is started by pumping a small
amount of reducing agent solution into the
reactor. Once the polymerlzation has started,
the flow of reducing agent is adjusted to a
constant level and maintained throughout the
polymerization.
As indicated, a nonionic surfactant
and an anionic surfactant are employed. The
nonionic surfactant may vary from about 2.5 to
about 10 parts per 100 parts of vinyl acetate
monomer charged. Preferably about 2.75 to about
4 parts nonionic surfactant per 100 parts vinyl
acetate is used. In general, as the level of
nonionic surfactant is reduced, elastomers of
maximum Mooney viscosity tend to be produced.
However, the most favorable level of nonionic
surfactant is best established by experiment.
About 0.1 to about 1 part of anionic sur~actant
to lOO parts of vinyl acetate monomer may be
~3~
13
1 employed, whereas the preferred ratio is 0.25 to
0.75 part per 100 parts of vinyl acetate
monomer. All of the nonionic and anionic
surfactant may be present in the polymerization
medium at the outset, as hereinabove disclosed,
or, if desired, one or both may be added
incrementally, either totally or in part.
Nonionic surface active agents which
can be employed for the improved polymerization
process of this invention are any of the
conventional nonionic surfactants known for the
preparatio~ of EVA and VAE copolymer and
terpolymer latices. These products typically
contain one or more water-soluble oxyalkylene
moieties, such as a polyoxyethylene or
polyo,cy(ethylene/propylene) group. Useful
nonionic surfactants of this type are
described in U.S. Patent Nos. 2,674,619,
2,677,700, and 4,287,329. Mixtures of one
or more nonionic surfactants may also b~
advantageously employed for the inter-
polymerization. Tetronic 908 is a par-
ticularly useful nonionic surfactant.
Just as with the nonionic surfactants,
conventi.onal anionic surface active agents
heretofore known for the emulsion polymerization
of ethylene with vinyl acetate are also useful
for the present process. Among the many anionic
surface active agents which can be used herein
are *Triton X-200 (Rohm & Haas Co.), a sodium
salt of an alkylaryl polyether sulfonate; Triton
-
*Trade mark
~ .
:
13Q~
1 QS-9 (Rohm & Haas Co.), a phosphate ester;
*Alipal CO 433 (GAF), a sodium salt of sulfated
nonylphenol (ethyleneoxy) ethanol, *Dupanol ME
Dry (Du Pont), a sodium lauryl sulfate; and
*Emersal 6453 (Emery Chemicals), a 25~ active
a~ueous solution of sodium lauryl ether sul~ate.
Emersal 6453 is a particularly useful anionic
surfactant.
The catalysts used in the
copolymerization reaction are any of the known
and conventional free radical polymerization
catalysts heretofore used for the preparation of
EVA copolymer latices and include inorganic
peroxygen compounds such as hvdrogen peroxide,
sodium perchlorate and sodium perborate;
inorganic persulfates such as sodium persulfateJ
potassium persulfate and ammonium persulfate.
The catalyst is generally utilized at a level of
from about 0.05% to about 3% by weight based on
the vinyl acetate monomer charged. Most usually
about 0.2% to 1~ catalyst is employed. Ammonium
persulfate is a particularly useful catalyst.
It is preferred in the process of this
invention to initiate and maintain the
polymerization by gradually adding a small
amount of a reducing agent (sometimes called a
co-catalyst) to the reactor. Initiating species
are produced by reaction of the catalyst with
the reducing agent (redox activation). The
reducing agent may be sodium hydrogen sulfite,
sodium meta bisulfite, sodium hydrosulfite and
sodium formaldehyde sulfoxylate. Sodium
*Trade mark
7 A
' ~ ~si~
?8~3-
1 formaldehyde sulfoxylate is preferred. The
reducing agent is conveniently added in aqueous
solution. The concentration of the reducing
agent will broadly range from 0.1 to 2 weight
percent and, more usually, from 0.25 to 0.75
weight percent of the aqueous solution.
Low levels of ions derived from
variable valence transition metal salts are
advantageously utilized as promotors during
redox initiation of these polymerizations.
Ferrous sulfate heptahydrate is a preferred salt
for this purpose. From about 0.0005 to about
0.05 part and, more preferably, 0.001 to 0.01
part of the salt per 100 parts of vinyl acetate
monomer is utilized. Also, an alkaline
buffering agent such as sodium bicarbonate,
ammonium bicarbonate, sodium acetate, and the
like~ may be added to the aqueous system to
maintain the pH at the desired value. The
amount of buffer is generally about 0.10 to 1.0%
by weight, based on the vinyl acetate monomer.
While it is not essential for the
interpolymerization process of the present
invention, a protective colloid o~ the type
generally known to the art can be included
during the polymerization. Such known and
conventional protective colloids as the
partially and fully hydrolyzed polyvinyl
alcohols; cellulose ethers, e.g., hydroxymethyl
cellulose, hydroxyethyl cellulose, ethyl
hydroxyethyl cellulose and ethoxylated starch
derivatives; the natural and synthetic gu~s,
16
l e.g., gum tragacanth and gum arabic; polyacrylic
acid, and poly(methyl vinyl ether/maleic
anhydride), are well suited for use herein.
- For the improved process of this
invention whereby high Mooney viscosity
interpolymers of vinyl acetate, ethylene and
reactive halogen-containing monomers are
produced and which upon vulcaniæation using a
soap/sulfur cure system have enhanced physical
properties, the halogen-containing cure site
monomer is charged after the polymerization of
the ethylene and vinyl acetate is initiated and
as the polymerization proceeds, i.e., during the
course of the polymerization. The VCA or other
halogen-containing monomer is introduced into
the polymerization continuously or
intermittently (semi-continuously). While the
cure site monomer can be &dded continuously or
discontinuously over the entire polymerization
period, more commonly the time period over which
the cure site monomer is added comprises at
least about one-twentieth to about three-fourths
of the total polymerization period. The total
polymerization period is the time from the
initiation of the polymerization until the
ethylene pressure is released and the
polymerization terminated, usually about 8-10
hours.
If addition is made in an intermittent
manner, periods of cure site monomer addition
alternate with periods of monomer withholding.
There may be from two to one hundred or more
~3U~
17
l periods of cure site monomer addition and a
corresponding number of periods of cure site
monomer withholding. Most generally, when
- adding the VCA on an intermittent basis from
five to about ten such periods of VCA cure site
monomer addition and withholding are utilized.
The length of the addition periods may vary
widely and the monomer addition periods may be
equal to the monomer withholding periods or
different. The rate of cure site monomer
addition within each addition period may be
constant or variable and may vary from period to
period. The said rate can be varied, for
example, by varying the rate of pumping of the
cure site monomer feed pump. If desired, the
rate of cure site monomer addition may be
increased until the incremental additions are
almost instantaneous as, for example, with a
suitable high pressure injection device.
The vinyl chloroacetate or other
halogen-containing monomer can be added to the
polymerizate either neat or in combination with
the vinyl acetate monomer. When diluted with
vinyl acetate the halogen-containing monomer
will constitute at least 20 weight percent of
the mixture. It has quite unexpectedly been
found that by adding the VCA during the
polymerization in this manner that elastomers
having improved physical properties are
obtained. It is also within the scope of the
present invention to add VCA in vinyl acetate
monomers to the polymerization reaction in a
;iL3~
1 periodic manner as disclosed above but at
concentrations of 20 weight percent of VCA or
more in vinyl acetate monomer.
The pressure at which the E/VA/VCA
emulsion interpolymerization is performed may
vary broadly over a range of as little as 400
psig to as high as about 4000 psig. The
pressure in the polymerization is maintained by
feeding ethylene into the reactor by means of an
ethylene compressor. The pressure selected will
depend on the ethylene content desired in the
terpolymer elastomer.
The ethylene pressure may be held at a
relatively constant level throughout the
polymerization, however, in an especially useful
embodiment of the invention the ethylene
pressure is increased during the polymerization
as the cure site monomer is being introduced as
hereinabove disclosed. When the ethylene
pressure is increased it generally ranges from
about 400-900 psig at the start of the
polymerization to about 2000-4000 psig at the
end of the polymerization period. Preferably,
the ethylene pressure is increased to about 1200
psig within the first 1 to 2 hours of the
polymerization and thereafter is gradually
increased to the maximum pressure by the end of
the total polymerization period. By regulating
the ethylene pressure in this manner, E/VA~VCA
interpolymer elastomers containing from abou~ 55
to about 65 weight percent of incorporated vinyl
acetate and having high tensile strengths upon
~3~
, 19
1 vulcanization using a conventional soap/sulfur
cure system are produced.
When the polymerization process of the
invention is carried out in a manner approaching
continuous operation, as in two or more reactors
in sequence, it is often convenient to operate
each of the successive reactors at successively
higher bu~ constant ethylene pressures while
preferably periodically introducing cure site
monomer.
The temperature of the polymerization
can range from about 5C to about 80C, however,
temperatures of 20C to 55C are preferred. It
is, of course, recognized by those skilled in
the art that at the lower temperatures a
reducing agent must be employed to generate the
free radicals required for initiation of the
polymerization by reacting with the
aforementioned catalyst. The total time of
polymerization may be as little as 1 hour up to
as long as 20 hours. However, polymerization
times from about 8 to about 10 hours are most
common.
The interpolymer elastomers are
recovered from the polymerization in the form of
a latex. The interpolymer itself may be
isolated by adding to the latex a hot saturated
aqueous solution of a salt, such as sodium
sulfate, sodium chloride or the like.
Alternatively, the interpolymer may be recovered
from its latex by other methods known to the
art, e.g. freezing, spray-drying, etc.
~3C~V8~
1 Preferably, the recovered interpolymer is next
washed to remove residual surface active agent,
catalyst residue, salt used for coagulation and
other extraneous substances, and dried.
- The interpolymer elastomers obtained
by the process of this invention are readily
compatible with conventional soap/sul~ur cure
systems and compounding ingredients. The soap,
sulfur and other ingredients can be blended into
the elastomer by procedures known to the art.
The blending may, if desired, be done with any
suitable blending equipment such as a two-roll
rubber mill, Banbury mixer, twin screw
processor, etc.; a two-roll rubber mill is most
co~monly used.
Soap/sulfur vulcanization systems
typically include a long-chain carboxylic acid
salt or soap, sulfur, a long-chain fatty acid,
and an antioxidant. This type of sulfur
vulcanization technology differs from
conventional sulfur w lcanization of elastomers
containing carbon-carbon double bonds as cure
sites and is more fully disclosed in U.S.
Patents 3,458,461, 3,939,128 and 3,972,857.
Various filler/reinforcing agents may
be employed, although it is within the scope of
this invention to vulcanize un~illed
compositions. Examples of filler/reinforcing
agents are various types of carbon black, e.g.,
furnace blacks, channel blacks, thermal blacks,
and the like. Specific types of carbon black
:: : :
~,
.j ,
~`~21 8~
1 are fast extruding furnace black (Industry
Designation: FEF: ASTM No. N550),
semireinforcing furnace black (Industry
- Designation: SRF; ASTM No. N774), and high
abrasion furnace black (Industry Designation:
HAF; ASTM No. N330). Of these carbon blacks,
N550 carbon black is particularly advantageous.
Other common filler/reinforcing agents that can
be used include various types of silicas,
aluminas, and clays, diatomaceous earthl barium
sulfide, glass fibers and the like. In general,
the best strength properties are achieved where
the filler/reinforcing agent is employed at a
level of about 30-60 parts per 100 parts of the
elastomer. However, this value is only a
guideline and from about 25 to 100 parts
filler/reinforcing agent may be employed for
certain applications.
If desired, minor amounts of other
modifying resins or elastomers can be blended
with the terpolymer elastomers of this
invention. These include various polyethylenes,
polypropylenes, EVA and VAE copolymers,
polyvinyl chloride, polychloroprene,
polyacrylate rubbers, polyurethanes, chlorinated
polyethylene, polyesters,
ethylene-propylene-diene monomer (EPDM)
terpolymers, ethylene-methyl acrylate
elastomers, ethylene-butyl acrylate elastomers,
butadiene-acrylonitrile elastomers, and other
known elastomers and resins. Typica~ly the
modifying resin or elastomers will comprise from
'
.~, .,~, .... ...
~3{~80~.
22
l about 10 to about 40 weight percent of the
blend.
The following examples illustrate the
- invention more fully. All parts and percentages
are on a weight basis unless otherwise
indicated. Chemicals used, such as vinyl
chloroacetate, ammonium persulfate, vinyl
acetate, ethylene, stearic acid, sulfur, etc,,
were good to high purity grades obtained from
commercial suppliers or prepared internally.
Sodium formaldehyde sulfoxylate dihydrate was
used as the reducing agent throughout.
The chlorine content o~ the
interpolymers was determined by a modified
Schoeniger method. The vinyl ester content was
determined by a saponification procedure. The
abbreviation VAM signifies vinyl acetate
monomer. Mooney viscosity, M~(l + 4) l~ 212C,
was determined according to ASTM D 1646-68 and
is often abbreviated MV. Gel contents of the
elastomers were determined by placing 3 grams of
the polymer in 600 ml of xylene in a covered
beaker and stirring for 24 hours with a magnetic
stirrer at 80-90C The solution was filtered
hot through a weighed coarse porosity glass
frit. Any gain in weight was considered to be
gel and expressed in percentage of the original
sample weight.
Tensile strength and elongation of
vulcanized elastomers were determined by ASTM D
412. Whereas tensile and elongation values were
measured at different cure tim~s, only the
: ,.
13~o~
~: 23
1 maximum tensile strength and corresponding
percent elongation are reported in the examples
since this represents the maximum physical
strength attainable ~or the particular
w lcanizate.
"
~ 20
;
:
~:
:: ~35
: , '
, ..,i
~l3~8~
24
EXAMPLE I
_
In accordance with the process of the
present invention, a E/VA/VCA terpolymer
elastomer was prepared. A one-gallon pressure
reactor equipped with an efficient agitator and
cooling jacket was employed for the
polymerization and charged as follows:
Grams
-
Deionized Water
850
Nonionic Surfactant [Tetronic (trademark) 908]
26
Anionic Surfactant ~Emersal (trademark) 6453]
Ammonium Persulfate
Ferrous Sulfate Heptahydrate
0.02
Sodium Acetate
3.2
VAM
800
After purging air from the reactor by pressuring
with nitrogen and releasing the pressure several
times, the reactor was pressured with ethylene
to 1090-1200 psig and heated to about S0C with
agitation. About 25 mls of a 0.2 weight percent
aqueous solution of sodium formaldehyde
.
13~)08~
l sulfoxylate reducing agent was then added to
initiate the polymerization. After 50 minutes,
4.~. grams vinyl chloroacetate was pumped into
the reactor over a 10-minute period. Comparable
additions of VCA were made during about the last
10 minutes of each of the next 5 hours until a
total of 25 grams VCA was added. The
polymeriæation was then allowed to continue for
an additional 2 hours. Throughout the
polymerization tincluding the addition periods)
the temperature was maintained at 50C, ethylene
pressure was maintained between about 1280 and
1400 psig, and the solution containing the
reducing agent was continuously added at a rate
sufficient to maintain the polymerization.
At the conclusion of the 8-hour
polymerization period, water was added to reduce
the viscosity of the latex and facilitate
discharge from the reactor and a small amount of
a p-methoxyphenol was added to the latex as a
chain-stopper. A hot concentrated aqueous
sodium sulfate solution was then added to the
latex to coagulate the E/VA/VCA elastomer.
After washing with water to remove salts and
other e~traneous materials, the polymer was
dried in a vacuum oven. The E/VA/VCA
interpolymer tMV 35.5) showed no evidence of gel
and contained 60.3% VA and 0.51% Cl.
:
~ ~
.
~ .
~3~80~.
26
l In order to evaluate the vulcanizate
properties, the elastomer was vulcanized using a
soap/sulfur cure system. For the vulcanization,
the E/VA/VCA interpolymer was compounded as
follows:
Pa _
E/VA/VCA terpolymer
100
Agerite Resin D (trademark)
1.0
Sulfur
0.8
Stearic Acid
2.0
N550 Carbon Black
~1 . 0
Premix of equal parts 8.0
N550 Carbon Black and
Sodium-2-Ethylhexanoate
The ingredients were milled into the elastomer
at 150-170F in the order shown using a standard
two-roll laboratory mill having 2.5 inch
diameter rolls. Total milling time was 2Q-25
minutes. The E/VA/VCA elastomer exhibited good
behavioral characteristics on the mill as a
:
result of the high Mooney vi~scosity of the
elastomer. Tensile strength ~ànd percent
~ elongation at break were determined using
specimens obtained from vulcanized sheets of the
;~ ; elastomer which were cured in a~press at 170C~
.
:
130~3V~
27
l Optimum w lcanizate properties (tensile strength
1840 psi at 380% elongation) were developed
after 15 minutes cure. Unless otherwise
- specilied, 0.8 g of sulfur was used in all
subsequent vulcanizations.
When the polymerization was repeated,
except that the ethylene pressure was maintained
between 1260 and 1360 psig and the total
polymerization time was 9 hours, the resulting
VA/E/VCA terpolymer contained 58.6% VA and 0.50%
Cl. The elastomer contained no gel and had a
Mooney viscosity of 34.5. 'rhe interpolymer
elastomer, compounded and cured as hereinabove
described, had a tensile of 1840 psi and
elongation at break of 390%.
Comparison A
To demonstrate the improved results
obtained by the process o~ the present invention
and the criticality of adding the vinyl
chloroacetate cure site monomer continuously or
intermittently during the polymerization, the
following comparative experiment was conducted.
For the polymerization the following ingredients
were charged to a reactor.
Grams
Deionized Water
850
Nonionic Surfactant lTetronic (trademark) 908]
26
: ~ ~ 35
'
. :,
~L3~30~
28
1 Anionic Surfactant [Emersal (trademark) 6453
; 4
Ammonium Persulfate
Ferrous Sulfate Heptahydrate
0.02
Sodium Acetate
3.2
VCA
37
VAM
800
As in the procedure of Example I, the
polymerization was initiated and maintained by
the addition of aqueous sodium formaldehyde
sulfoxylate (0.5%) aft~r the reactor was
pressurized with ethylene. The solution
containing the reducing agent was metered into
the reactor throughout the course of the 8.5
hour polymerization run. Ethylene pressure
ranged between 1150 and 1380 psig during the
polymerization. The E/VA/VCA terpolymer was
coagulated and recovered in the usual manner and
contained 60.0~ VA and 0.78~ Cl, with a Mooney
viscosity of 34.
Three compounded formulations were
prepared employing the above-prepared terpolymer
in accordance with the following recipes:
: : :
' ~ :
.
2~93~80~
l Comp A(l)
Comp A~2) Comp A(3~
E/VA/VCA Terpolymer 100 100
100
N774 Carbon Black 45 45
Agerite Resin D (trademark) 1.0
1.0 1.0
Stearic Acid 2.0
2.0 2.0
Sulfur 0.3
0.5 0.91
Sodium 2-ethylhexanoate 4.0
; 4.0 4.0
The compositions were milled and cured at 170C
in the usual manner and tensile and elongation
val.ues determined. Maximum tensile and
elongation obtained for A(l), A(2), and A(3)
were 1270 psi (160%), 1480 psi (130%) and 1300
psi (110%), respectively. It is evident from a
comparison of these tensile and elongation
values with t~ose of Example I that the E/VA/VCA
elastomers prepared in accordance with the
present invention develop significantly higher
tensile properties when vulcanized using
conventional soap/sulfur cure systems.
3o
: : :
:, ~
;::
13~8V~
- 30
EXAMPLE II
To demonstrate how carbon black
affects the tensile/elongation properties of the
E/VA/VCA elastomers after soap/sulfur
vulcanization Example I and Comparison A were
repeated. Different carbon blacks, N550 and
N774, were used in compounding the E/VA/VCA
elastomers prepared in accordance with Example I
and Comparison A. The E/VA/VCA elastomers
prepared by the method of Comparison A
(identified as Elastomer IIA), in which all the
VCA monomer was placed in the reactor at the
start, contained 57.7 wt. % VA, 0.74 wt. % Cl,
and had a Mooney viscosity of 34. The E/VA/VCA
elastomer obtained by the method o~ Example I
wherein the VCA monomer was added periodically
(identified as Elastomer IIB) contained 64.3 wt.
% VA, 0.71 wt. % Cl, and had an Mooney Viscosity
of 36.5,
Elastomers IIA and IIB were compounded
and vulcanized as disclosed in Example I, except
for varying the carbon black, with the
following results:
3
~ 35
13~80~,
31
1 Elastomer No. IIA
IIB
Method of Adding
VCA in Synthesis__ at Start _
Periodically
Carbon Black Used
N774 N774 N550 N774 N550
Cure Operator I II II
lO II II
Tensile, psi
3 min. 1130 1020 1170
1430 1740
7 min. 1150 1050 1230
151400 1600
15 min. 1110 1010 1190
1560 1880
30 min. 1120 1130 1200
1480 1830
20Elongation, %
3 min. 190 140 130
3~0 310
7 min. 150 140 140
340 250
2515 min. 150 140 130
400 310
30 min. 160 160 140
370 330
3O From the above data it is evident that the
improved process of the present invention in
which the VCA cure site monomer is in~roduced
::
.
~3~0~01;
32
1 periodically during the polymerization provides
higher tensile values with both N774 and N550
carbon black. N550 carbon black, however,
uniformly gave higher tensiles and therefore was
employed in all subsequent examples of the
present invention unless otherwise stated.
13~
-~ 33
EXAMPLES III AND IV
To demonstrate the ability to vary the
E/VA/VCA interpolymer composition, two
experiments were carried out following the
procedure of Example I by increasing the amount
of vinyl chloroacetate charged. The VCA monomer
was charged in six equal portions during the
last 7-10 minutes of each of the first six hours
of the polymerization. Experimental details
which differ from those described in Example I
are set forth in the table. The elastomer and
w lcanizate are also characterized in the table.
.
:, :
~ 35 ~ ~
~3(~
34
l EX. III
- EX. IV
-
Ethylene Pressure (psig)
1270-1430 1110-1160
Vinyl Chloroacetate (Total Grams Charged) 30
Polymerization Time (Total Hours) 9
Elastomer:
~ Vinyl Acetate
61.4 67.3
% Chlorine
0.65 0.91
Mooney Viscosity 33
39.5
Vulcanizate:
Tensile Strength (psi) 1830
1800
Elongation (%) 340
260
~ 3
: 35
:
~.
.
~13~
EY~IPLES V AND VI
Further process variation is
demonstrated by the following two experiments
wherein the ammonium persulfate-sodium
sulfoxylate catalyst system was replaced with a
hydrogen peroxide-sodium formaldehyde
sulfoxylate catalyst system. For these
experiments the following charges were made:
Grams__
EX. V
EX. VI
Deionized Water 850
~50
Tetronic (trademark) 908 26
26
Emersal (trademark) 6453 4
Sodium Formaldehyde Sulfoxylate 1.5
Ferrous Sulfate Heptahydrate 0.02
0.02
Formic Acid 0.4
0.4
V~M 800
800
The reactors were heated and pressurized with
ethylene in the usual manner; however, to
initiate and maintain the polymerization aqueous
: hydrogen peroxide (0.5%) was continuously
metered into the reactor. Vinyl chloroacetate
:
.
~3~B~
36
1 was charged in 6 equal portions during the last
10 minutes of each of the first 6 hours of
polymerization. A total of 32.5 grams vinyl
chloroace~ate was charged for each reaction.
The E/VA/VCA terpolymer elastomers were
recovered, co~pounded, and vulcanized in the
usual manner. Polymerization times and ethylene
pressures for the reaction and characteristics
of the unvulcanized elastomeric products were as
ollows:
EX. V
EX VI
Ethylene Pressure (psi) 1280-1480
12~0-1410
Polymerization Time (Total Hours) 9
8.5
Elastomer:
~ Vinyl Acetate 62.8
63
% Chlorine 0.7
0.71
Mooney Viscosity 24.5
~6
Vulcanizate:
Tensile Strength (psi) 1810
1870
Elongation (%) 320
310
~ 35
.
.
~3~
37
EX~LR VII
This experiment was conducted to
demonstrate the further ability to improve
elastomer properties. The reaction was carried
out in accordance with the general procedure of
Example I except that the ethylene pressure was
increased during the polymerization. All of the
vinyl acetate monomer was charged to the reactor
at the outset and the vinyl chloroacetate (32
grams) was charged intermittently during the
first six hours' polymerization. The initial
ethylene pressure was 720 psig; however, the
pressure was increased over the first 1~ hours
of polymerization to 1200 psig. The ethylene
pressure was further increased over the
remainder of the polymerization run (total
polymerization time 8.5 hours) to a final
pressure of ~100 psig. The E/VA/VCA terpolymer
was recovered by the standard procedure and upon
analysis shown to contain 65.1~ VA and 0.85% Cl.
The terpolymer had a Mooney viscosity of 44.
The E/VA/VCA elastomer was compounded
in accordance with the formulation of Example I
and w lcanized at 170C for 30 minutes. The
w lcanizate after a 30-minute cure time had a
tensile strength of 1920 psi and 240 percent
elongation. It is apparent from the above data
; that further improvement in the Mooney viscosity
and tensile properties of E/VA/VCA elastomers is
possible when, in addition to having all of the
VAM present at the outset of the polymerization
3~
.
~3 0 ~a
. 38
1 and introducing the VCA intermittently to the
reactor during polymerization, the ethylene
pressure is increased over the course of the
polymerization.
.
3
35 : ~ :
: :::
,.~, ,.. - .
. . '~ , . .
~3~8C~
39
E~YAMPLE VIII
Example VII was repeated except that
the total polymerization time was increased to
9.75 hours. For this interpolymerization, the
initial ethylene pressure was 720 psig. After
commencement of polymerization, the ethylene
pressure was increased to 1200 psig within one
hour and in the remaining 8.75 hours gradually
increased to 2450 psig. The E/VA/VCA elastomer
had a Mooney viscosity of 36 and contained 62.4%
VA and 0.93~ Cl. The elastomer had a maximum
tensile of 1940 psi at 240 percent elongation
upon vulcanization at 170C using a standard
soap/sulfur cure system.
, 25
3
13~ 0~
EXAMPLE IX
The ability to add the vinyl
chloroacetate cure site monomer continuously is
demonstrated by the following example which
followed -the general procedure of Example I and
utilized the same reactant charge. After the
reactor was pressured with ethylene to about
132Q psig the polymerization was initiated by
the addition of the aqueous sodium formaldehyde
sulfoxylate solution. After 3 hours 9 vinyl
chloroacetate (40 grams) was continuously
metered into the reactor over a l~-hour period
and the polymerization continued for an
additional 5~ hours. The reducing agent
solution was continuously added over the entire
polymerization period and the ethylene pressure
was maintained in the range 1320 to 1410 psig.
The E/VA/VCA terpolymer, recovered in the
usual manner, had a Mooney viscosity of 36 and
contained 58.3% VA and 0.47 weight percent Cl.
Upon vulcanization the elastomer had a tensile
of 1680 psi and elongation of 280 percent.
~ 25
:;
3o
~ ~ .
~ ,... ... ..
41 ~3~80~
EXAMPLE X
1 A variation on the continuous addition
procedure is demonstrated by the following
- example wherein the vinyl chloroacetate monomer
was diluted with a portion of the vinyl acetate
~ 5 monomer. The reaction was carried out similar
to Example VIII except that only 700 grams VAM
was charged to the reactor. The remaining 100
grams VAM was combined with 32 grams VCA t24%
concentration of VCA) and the resulting solution
continuously and uniformly metered into the
reactor over a period of six hours after
initiation of the polymerization. Ethylene
pressure ranged from 1240 psig to 1410 psig
during the run (total polymerization time 7~
hours). The resulting E/VA/VCA elastomer had a
Mooney viscosity of 33 and contained 59.4~ VA
and 0.60% Cl. Conventional soap/sulfur
vulcanization at 170C produced a w lcanizate
having maximum tensile of 1730 psi and 260
percent elongation after 7 minutes cure.
Comparison B
To demonstrate the criticality of
having all or at least a major portion of the
vinyl acetate monomer present at the outset of
polymerization, the procedure of Example X was
repeated except that 300 grams VAM and 13.9
grams VCA were charged to the reactorO A
solution o~ 23.1 grams vinyl chloroacetate in
500 grams VAM (4.7~ concentration o VCA) was
then prepared and continuously and uniformly
.
.
,,
31 3(~ 30~
.
42
l metered into the reactor during the first 6.3
hours of polymerization. Ethylene pressure
ranged between 1160 psig and 1380 psig
throughout the run (total polymerization time 10
hours). The resulting E/VA/VCA elastomer
contained 55.7% VA and 0.81% Cl. The elastomer
had a Mooney viscosity of only 13 and upon
vulcanization (using N774 carbon black) had a
maximum tensile strength of only 1010 psi and
250 percent elongation. By repeating the
polymerization at a lower ethylene pressure
(920-960 psig) 9 it was possible to increase the
VA and VCA contents o~ the elastomer (62.~% VA
and 1.02% Cl) and slightly improve the tensile
value of the vulcanizate (1240 psi at 200%
elongation). The Mooney viscosity of the
elastomer, however, remained essentially
unchanged (MV 14). Even if N550 carbon black
had been used instead o~ N774 in the
compounding, it would not be possible to develop
tensiles comparable to those obtained with the
elastomer of Example X.
: :
'
.
. .
