Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
337836
SOLID-STATE POLYMERIZATION PROCESS FOR
INCREASING THE MOLECULAR
WEIGHT OF COPOLY(ARYLENE SULFIDE)
The invention relates to a solid-state
polymerization process for increasing the molecular
weight of a copoly(arylene sulfide) by heating the
copoly(arylene sulfide) in the presence of an inert
gas.
Poly(arylene sulfide) resins are
thermosetting-thermoplastic polymeric materials with
good thermal stability, unusual insolubility,
resistance to chemical environments and inherent
flame resistance. These resins additionally have
good electrical insulative properties which make them
ideal for electrical and electronic applications.
Their excellent resistance to chemical degradation
makes them ideal for use in chemical environments
which involve organic solvents, and strong mineral
acids, such as coatings for pipes, tanks, pumps and
other equipment.
Poly(phenylene sulfide) is a commercial product
which is generally produced by reacting
i p-dichloro-benzene with sodium sulfide in a polar
organic solvent. This process if known as the
Edmonds and Hill polymerization procedure and is
disclosed in U.S. 3,354,129. Another approach to
preparation of poly(phenylene sulfide) is the
Macallum process whereln p-dichlorobenzene and sulfur
are reacted in the presence of sodium carbonate.
This procedure is disclo~ed in U.S. 2,513,188 and
U.S. 2,583,941.
The poly(phenylene sulfide) whlch is formed in
the Edmond and Hill process has only a modest
1 3~7~36
molecular weight on the order of 10,000-40,000 and
has relatively low melt viscosity. Hi8her molecular
weights can be obtained by heatin8 the PPS in the
presence of oxygen. During heating, the molecular
weight of the PPS increases due to a variety of
chemical reactions including oxidation, crosslinking
and chain extension. These curing reactions result
in polymers which have inherent brittleness and
reduced drawing capability while only achieving
modest increases in molecular weight. Additionally,
poly(phenylene sulfide) which is produced by
polymerization in the presence of sulfide and/or
hydrosulfide salts, such as sodium sulfide and sodium
hydrosulfide, has a residual content of inorganic
1~ salt present in the polymer. These residual salts
are, for example, sodium chloride and sodium sulfide
resulting from the combination of the sodium cation
with chlorine or sulfide from the starting
materials. The presence of these residual ~alts in
the polymer increases the corrosive nature of the
polymer and can cause a deterioration in the drawing
or spinning characteristics of the polymer. Residual
salts can also result in breakages in the spun fibers
and additionally contribute to plugging and clogging
of the spinnert holes.
U.S. 3,354,129 discloses that in Column 6 the
polymer prepared in accordance with the disclosure of
U.S. 3,354,129 "can be heat treated in the absense of
oxygen or with an oxidizing agent either under vacuum
or at atmospheric pres~ure or ~uperatmospheric
pressure" in order to increase the molecular weight
of the polymer. However, in Example 1 a run is
reported that initially gives brittle polymer when
molded at 310C. When this sample was treated under
vacuum for 3 hours at 340 to 360C, it yielded a
brittle part. The same material when worked in a
- 3 - 1 3 ~ 7 ~ 3 6
molten state in the presence of air became tough.
Further in Example 6 there is a specific comparison
of heat treatment in air and nitrogen. The
nitrogen-treated sample is brittle, whereas the
air-treated one is tough. The nitrogen-treated
material has increased in melt viscosity an
insignificant amount in contrast to the air-treated
sample.
U.S. 3,919,177, U.S. ~,038,259 and
U.S. 4,038,260 for example all disclose that
poly(phenylene sulfide ". . . can be cured through
crosslinking andlor chain extension, for example, by
heating at temperatures up to about 480C in the
presence of a free oxygen-containing gas to provide
cured products having high termal stability and good
chemical resistance." It is thus apparent that the
curing in air to obtain a higher molecular weight,
yet branched polymer is a normal teaching of the
art. Increasing the molecular weight under inert
conditions conversely is not taught.
Broadly, solid state polymerization is well
known in the art for other polymers, such as
polyesters. Specifically, the heating process of
this invention is known to be useful for increasing
the molecular weight of polyesters.
We have now discovered a solid-state
polymerization process for increasing the molecular
weight of certPin copoly(arylene sulfides) wherein
the polymer is heated either under vacuum or in the
presence of an inert gas. Our invention can be
broadly defined as a process comprising heating
within a heating zone at a temperature in of at least
200C a crystalline polymer corresponding to the
structure:
I (-A-S~ X(-A S S )x _In
1 337~33~
- 4
wherein A is a divalent substituted or unsubstituted
aromatic radical, x is in the range of 0.5 to 0.001
and n is at least 200 wherein the volume of the
heating zone not occupied with polymer is either
under vacuum or is occupied with an inert gas.
The polymer useful in this invention is a
copolymer wherein the vast ma~ority of units in the
copolymer are the (-A-S-) unit and the number of
(-A-S-S-) or disulfied units are small compared to
the number of (-A-S-) units. Generally, the number
of (-A-S-S-) units is in the range of 0.5 to 0.001,
based on the combined number of both (-A-S-) and
(-A-S-S-) units. Thus, the copolymer prepared by the
' process of the invention can be represented as
(-A-S-)l_X(-A S S )x
7 where x is in the range of 0.5 to 0.001. The
sequence of (-A-S-) and (-A-S-S-) units is thought to
be random throughout the moleculsr chain. When x is
in the range of 0.5 to 0.2 the polymers obtained when
A is p-phenylene are amorphorus and can be
crystallized only with difficulty. When x is in the
range of 0.2 to 0.1 the polymers obtained can be
thermally crystallized and have crystalline melting
points of 230 to 260C. When x is in the range of
0.1 to 0.05 the polymers obtained have moderate
crystallization rates and the crystallized polymers
can be annealed to high crystalline melting points
(280 to 290C) and show Tch (temperature of
crystallization on heating) and Tcc (temperature of
crystallization on cooling) at increasingly lower and
higher temperatures, respectively, indicative of
increasing rates of crystallization. When x is in
the range of 0.05 to 0.001 the crystallization rate
increases rapidly with decreasing x.
The size of the polymer chain can conveniently
be expressed as the total number of each kind of unit
_ 5 - l 3 ~ 7 ~ 3 6
in the chain. Therefore, the copoly(arylene sulfide)
prepared by the process of thls invention can be more
specifically expressed as corresponding to the
structure
(-A-S-)l_X(-A S S )x
--n
I wherein n, the degree of polymerization, is at least
200 and is preferably in the range of 500 to 5,000 as
; 10 determined by melt viscosity measurement at 300C.
The degree of polymerization when A is p-phenylene
can be calculated using the relationship log(n) =
1.473 ~ 0.2873 x log(melt viscosity) where melt
viscosity is measured in poise.
15These copolymer can be prepared by a process
wherein a diiodoarylene compound corresponding to the
structure
! I-A-I
where A is a divalent arylene radical is reacted with
elemental sulfur to produce a substantially linear
copoly(arylene sulfide) having both (-A-S-) units and
(-A-S-S-) units.
Diiodoaromatic compounds which can be utilized
in the present process include unsubstituted or
substituted aromatics which have two iodine
substituents. Suitable diiodoaromatic compounds
include hydrocarbon aromatics, nitrogen-containing
aromatics, sulfur-containing aromatics and
oxygen-containing aromatics. Typical hydrocarbon
aromatics include benzene and biphenyl, and condensed
ring aromatics such as naphthalene and anthracene.
Typical sulfur-containing aromatics include, for
example, thiophene and benzothiophene. Typical
nitrogen-containing aromatics include pyridine and
quinoline. Suitable oxygen-containing aromatics are,
for example, furan, dibenzofuran, etc. Substituted
diiodoaromatic compounds suitable for use with the
1 337~36
- 6
present invention include aromatic sulfones,
diarylethers, diarylcarbonyls, diarylsulfides and the
like.
The aromatic starting materials may be
substituted by one or more alkyl groups, preferably
alkyl groups having from 1-6 carbon atoms. Specially
preferred alkyl groups are methyl, ethyl, propyl snd
butyl groups. There is no limitation on the spatial
arrangement of the substituents, for example, the
substituents may be on a carbon ad~acent to an iodine
bearing carbon or may be on a carbon atom further
removed from the iodine bearing carbon.
Additional substituents on the aromatic
compounds may include phenyl, halogen, hydroxy,
nitro, amino, Cl_6 alkoxy, and carboxylate and
carboxylic acid su~stituents, as well as aryl
sulfones and aryl ketones.
Preferred diiodoaromatic compounds are the
diiodobenzenes, diiodonaphthalenes, diiodobiphenyls,
diiododiphenyl ethers and diiodotoluenes which may be
unsubstituted or substituted with any of the
~ubstituents noted above.
! Specific diiodoaromatic compounds suitable for
I the present invention include p-diiodobenzene,
m-diiodobenzene, p,p'-diiodobiphenyl,
m,p'-diiodobiphenyl, p,p'-diiododiphenyl sulfone,
p,p'-diiododiphenyl ether, 2,6-diiodonaphthalene,
p,p'-diiodobenzophenone, p-Diiodobenzene,
p,p'-diiodobiphenyl, and p,p'-diiododiphenyl ether
are most preferred.
The diiodoaromatic starting materials of the
present invention may be prepared by any suitable
process. For example, the diiodoaromatic compounds
may be prepared by standard liquid or gas phase
iodination reactions. A preferred method of
preparing the diiodoaromatic starting materials is
1 337~3~,
- 7
that disclosed in Patent Number 4,746,758, iQsued
May 24, 1988. Alternatively, the diiodoaromatic
compounds may be produced by a transiodination
process such as that disclosed in Patent Number
4,792,641 issued December 20, 1988.
Sulfur is reacted as elemental sulfur and may
consist of any of the standard forms which are
possible for elemental sulfur. That is, the sulfur
may be present in any of its allotropic modifications
such as orthorhombic cyclooctasulfur (S8) or any
other cyclic elemental sulfur such as any of the
cyclosulfur species having 6-12 sulfur atoms.
Additionally, any crystalline form of sulfur may be
used in the present reaction. Surprisingly,
impurities in the elemental sulfur do not appear to
affect the efficiency or selectivity of the present
polymerization reaction. The sulfur preferably has a
purity of about 98~-100~, although sulfur having a
lower degree of purity may be used. This lack of
sensitivity to the presence of impurities in the
sulfur is advantageous to the present process when
used as a commercial process since highly purified
sulfur is not required and the associated expense is
not incurred.
In the process of the present invention sulfur
reacts with a diiodoaromatic compound, eliminatin~
elemental iodine and forming the PAS as shown below.
nArI2 ~ nS ~ (-Ar-S-) ~ nI
The formation of polymer is not Qensltive to the
relative stoichiometry of the diiodoaromatic compound
and sulfur. Accordingly, an excess of sulfur or an
excess of diiodoaromatic compound may be used in the
polymerization process. When excess sulfur is used,
more disulfide linkages are observed in the polymer.
Decreasing amounts of sulfur result in decreasing
1 337~3~
- 8
levels of disulfide linkages in the final polymer.
When the diiodoaromatic compound is present in
excess, polymerization to high polymer can still
occur, if the excess diiodoaromatic compound is
removed during final polymerization.
The polymerization reaction is preferably
carried out in the absence of solvent by merely
- heating and reacting the sulfur and diiodoaromatic
compound. Under these conditions, the diiodoaromatic
compound itself acts as a solvent for the sulfur
which is melted thereby forming a substantially
homogeneous solution enabling a facile and complete
reaction.
In another embodiment, the diiodoaromatic
compound can be dissolved in an organic solvent which
is inert to the reaction conditions, i.e., which is
inert to reaction with iodine and sulfur. High
boiling inert aromatic solvents are preferred such
as, for example, aromatic hydrocarbons,
diarylsulfides, diarylethers and diarylsulfones. It
is preferable to use a solvent which corresponds to
the diiodoaromatic compound which is being
polymerized. Thus, for example, in the
polymerization of diiodobenzene with sulfur, one
might use benzene, toluene or naphthalene as a
solvent.
During the polymerization reaction between the
diiodoaromatic compound and sulfur elemental iodine
is produced and evolves from the reaction melt or
solution, or solid. Removal of the elemental iodine
provides a driving force for completion of the
polymerization reaction. The iodine may be removed
by passing a stream of air or an inert gas such as
nitrogen or argon over or through the reaction mass
at atmospheric or superatmospheric pressure or
alternatively by applying a vacuum to the reaction
_ 9 _ 1 33783~
apparatus. The elemental iodlne may be collected and
used as a commercial product or as a reactant for
further chemical processes. The present reaction,
therfore, does not result in wasted reaction products
since both the PAS and elemental lodine are useful
commercial chemical products.
The polymerization reaction is generally
conducted at a temperature above about 175C.
Although the reaction may be conducted at
temperatures below 175C, the polymerization reaction
is much slower. There is no particular upper
temperature limit on the polymerization reaction,
which may be conducted at any temperature below the
decomposition temperature of the diiodoaromatic
compound. For most polymerization reactions,
temperatures in the range of about 175 to 400C will
~ be sutiable, although for particular diiodoaromatic
compounds temperatures in excess of 400C may be
used. Particularly preferred temperature ranges are
from about 180 to 350C.
The reaction is generally conducted for a period
of at least one-half hour and is continued for up to
- about 10 hours or longer, and reaction times
approaching infinity are theoretically possible. The
exact reaction tlme will depend on the diiodoaromatic
compound, the engineering requirements of the
process, and the specific molecular weight, viscosity
and physical properties of the desired product.
The polymerization reaction may be carried out
in a batch reaction vessel or may be carried out as a
semi-continuous or continuous proceQs. ~8itation of
the reaction mixture is optional, however agitation
or stirring assists in the production and yield of
the polymeric product. Agitation of the reaction
mixture may be accomplished by any known method, such
as mechanical stirring or by passing a stream of
inert gas through the reaction mixture.
1 337~36
- 10 -
In a preferred embodiment, the polymerlzation
reaction is conducted on a continuous basis with the
diiodoaromatic compound and sulfur beinB combined in
a continuous staged reactor to form a reaction melt.
An inert gas such as nitrogen or argon is passed
through the melt, preferably in a countercurrent
direction, thereby accomplishing agitation and mixing
! of the reaction melt and at the same time removing
the elemental iodine which is evolved and sweeping it
out of the reactor. Alternatively, a vacuum may be
applied to the reactor to remove the elemental iodine
as it is ~enerated. It should be noted that the
reaction proceeds equally well under batch conditions
and combinations of batch and continuous processes
are considered to be well within the scope of the
present invention.
In accordance with the solid-state
polymerization process of this invention the
copoly(arylene sulfide) prepared by the process
broadly described by the preceding paragraphs must be
crystalline in order for the molecular weight to
increase during the heating ~tep. If the polymer is
not crystalline as a result of the process for its
preparation, it must be crystallized prior to the
heating step. This can be accomplished in accordance
with techniques well known in the art, such as
contacting the polymer with a suitable solvent, such
as toluene, or heating the polymer to a temperature
of about 30 to 100C above the polymer glass
transition temperature for sufficient time to develop
enough crystallinity to prevent fusing during the
subsequent higher temperature steps which usually
requires approximately 15 minutes or more heating
time.
In accordance with the invention the polymer
must be in relatively small units during the heating
1 337836
step in order for the molecular weight to build up.
Typically the solid polymer is granulated in accordance
with techniques well known in the art. Although the exact
particle size is not critical, particles which have a 0.25
inch screen are suitable for use in the invention.
The time used for the heating step can vary widely
depending on the temperature and desired molecular weight.
The higher the temperature the shorter the time and vice
versa. For example, good results can be obtained by
heating the polymer for several hours at 300C.
The temperature used for the heating step is at least
200C and preferably is in the range of 200C to within 5C
of the melting point of the polymer.
In accordance with this invention the polymer is
heated in the presence of either an inert gas or is heated
under vacuum. The inert gas can be any gas which does not
chemically react with the polymer, such as nitrogen or
argon.
The heating step can be accomplished using equipment
well known in the art for conducting solid-state
polymerization, such as a double cone rotary dryer or
fluidized bed reactor or moving bed reactor.
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.
,
~ 3 7 & 3 6
- 12 -
EXAMPLES
ExamPle 1
This example illustrates the preparation of the
polymer useful in the process of this invention. In
a 3-neck, 500-mL, round-bottom flask are combined the
following: 38.00 g sulfur (1.24 mol), 410.0 g
p-diiodobenzene (1.19 mol), and 0.2 g of
4-nitro-1-iodobenzene to act as polymerizatlon
catalyst. The flask is fitted with a column for
iodine takeoff, a mechanical stirrer, and the other
neck is stoppered. The column is attached via a
distillation head and takeoff tube to a receiver
flask which is cooled in dry ice. The flask is
maintained under about 200 torr pressure and immersed
in a 230C metal bath. After melting, the melt is
' stirrer mechanically. After about 30 to 45 minutes
reaction time, iodine begins to distill into the
receiver flask. The bath is maintained at 230C for
2 hours, 50 minutes after which time the temperature
is raised to 240C. After holding there for an
additional 40 minutes, the pressure in the reaction
flask is reduced to about 120 torr and held there for
0.5 hour. The pressure is reduced a8ain to about
60 torr, held there for an additional 0.5 hour,
reduced again to about 30 torr, held there for an
additional 0.5 hour, and finally the pressure is
reduced to 0.1 torr. Twenty minutes after the final
pressure reduction, the batch temperature is taised
to 250C. The re~ction is held an additional
1.75 hours after the time and removed from the bath.
The polymer melt is cooled under nitrogen, broken out
of the flask, and granulated in a Wiley mill fitted
with a 0.25 inch screen. A film pressed at 300C of
this material is partly tough and partly brittle.
DSC showed a Tg of 85C.
- 13 - I 3 7~ 7 ~ 3 ~
Example 2
This example illustrates the practice of the
invention wherein the polymer prepared in Example 1
is solid-state polymerized. Eighty grams of
granulated polymer from Example 1 were treated
5 times with 180 g portions of toluene to crystalline
the polymer. After additional treatment in a Soxhlet
extractor to remove iodine, the polymer was dried in
a 150C block in tubes under 0.2 torr pressure. The
polymer was then put in a heat block at 175C under
0.1 torr pressure and the temperature of the block
raised to 200C one hour later. Sample tubes were
pulled at 3 hours, 6 hours, 12 hours, and 24 hours.
Pressed films were all tough in all sections. Melt
viscosity measured at 300C illustrated the molecular
weight increase.
Heatin~ Time, Hours Melt Viscosity, Poise
3 5566
6 7004
12 13151
24 18440
i
ExamPle 3
This example illustrates preparation of the
polymer useful in the process of this invention and
also practice of the invention A separate
preparation of the polymer was carried out with the
following changes: the catalyst was 0.2 8 of
1,3-diiodo-5-nitrobenzene and the heating ~chedule
was altered to 2 hours, 5 minutes, at 230C, l hour,
35 minutes, at 240C, and the final polycondensation
was carried out at 0.8 torr, 250C for l hour,
55 minutes. Polymer yield was 93.8~.
1 337~36
- 14 -
The polymer was very brittle. Coherent films of
the material could not be pressed at the normal 300C
press temperature.
~ orty grams of granulated polymer W8S contacted
with toluene for a short time and divided into two
parts. An additional three, 20 g batches were placed
in solid-stating tubes. One each of the
1 toluene-treated tube and the untreated granules were
placed in a heat block under vacuum (0.1 torr) at
175C and held there 25 minutes before raising the
block temperature to 210C. After 21 hours, the
samples were removed and cooled under vacuum.
Pressed films are very tough. The same procedure was
repeated except that the toluene-treated sample was
held under a slow nitrogen flow whilte its control
was held under vacuum. Both samples after 21 hours
heating gave tough pressed films. The last untreated
sample was placed in the heat block and air drawn
over the sample during the course of heating. It
also produced a tough film but with very much darker
color than the other films.
Melt viscosity was measured on the above ~amples
at 300C for the solid-stated materials with the
I following results:
Heatin~ TreatmentMelt Viscosity, Poise
V~cuum 14740
Nitrogen 14940
Air 17820
The starting polymer was so low in melt
viscosity and also active in evolving vapors that it
was impractical to measure melt viscosity at 300C.
It was instead measured at 270C as 2294 poise.
- 15 - l 337~36
Example 4
This example illustrates that higher final melt-phase
preparation of the poly(phenyl sulfide) still results in a
polymer that is solid-state active towards molecular weight
buildup. The weights of Example 3 were duplicated along
with the process conditions until the reaction was under
o.l torr vacuum. It was held at that pressure at 250C for
1 hour after which the temperature was raised to 275C and
held there an additional hour. The final polymer yield was
92.8~ and the melt viscosity was 11450 poise at 300C.
After an initial thermal crystallization step at 175C,
this material was solid-state polymerized at 210C for 21
hours under vacuum. The resultant melt viscosity was 40180
poise at 300C.
Exam~le 5
This example further illustrates that higher final
melt-phase preparation of the poly(phenylene sulfide) still
results in a polymer that is solid-state active towards
molecular weight buildup. The weights of Example 3 were
duplicated along with the process conditions until the
reaction was under 0. 2 torr vacuum. It was held at that
pressure at 250C for 1 hour after which the temperature
was raised to 275C and held there an additional hour
followed by raising the temperature to 300C for 45
minutes. The final polymer yield was 93.7~ and the melt
viscosity was 48830 poise at 300C. After an initial
thermal crystallization step at 175C, this material was
solid-state polymerized at 210C for 21 hours under vacuum.
The resultant melt viscosity was 130900 poise at 300C.
.~
