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Claims  |
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What is claimed is:
1. A continuous process for concentrating a polymer solution having a
polymer concentration of from about 5 to about 50% by weight in the
substantial absence of gel formation wherein the solvent thereof has a
boiling point below the decomposition temperature of the polymer
comprising:
(a) heating the polymer solution to a temperature of not less than the
temperature at which the solvent thereof evaporates in the evaporation
zone of (b), which temperature is in the range of from about 20.degree. to
about 300.degree. C., by passing the solution through a heating zone;
(b) passing the heated polymer solution of (a) from the heating zone
through at least one orifice located in an evaporation zone, said
evaporation zone containing prior to passage of the polymer solution
therein a saturated atmosphere of the vapor of the solvent of the polymer
solution at a temperature not greater than the temperature of the polymer
solution after it exits the heating zone and not greater than the boiling
point of the vapor at the pressure present within the evaporation zone, to
thereby produce a polymer solution having a final concentration of from
about 8 to about 60% by weight polymer, based upon the total weight of the
polymer solution; and
(c) optionally admixing a part of said concentrated polymer solution of (b)
with the unconcentrated polymer solution of (a) prior to passage of the
resulting mixture through the heating zone.
2. The process of claim 1 wherein part of the concentrated polymer solution
of (b) is mixed with the unconcentrated polymer solution of (a) prior to
passage through the heating zone.
3. The process of claim 1 wherein the polymer solution comprises a solution
of a halogenated aromatic polyester in methylene chloride.
4. The process of claim 1 wherein the temperature of the vapor in the
evaporation zone is from about 10.degree. to about 200.degree. C. less
than the temperature of the heated polymer solution of (a).
5. The process of claim 1 wherein the polymer solution is selected from the
group consisting of cellulose acetate polymer dissolved in acetone or a
mixture of acetone and water, cellulose triacetate polymer dissolved in
methylene chloride or a mixture of methylene chloride and methanol,
polyvinylacrylonitrile dissolved in dimethyl formamide or dimethyl
acetamide, and polyvinyl chloride/vinylidene chloride dissolved in
acetone.
6. The process of claim 1 wherein the polymer of the solution is a
halogenated aromatic polyester which is the product of tetrabromobisphenol
A and a mixture of from about 55 to about 25% by weight terephthaloyl
chloride and from about 45 to about 75% by weight isophthaloyl chloride
dissolved in methylene chloride.
7. A continuous process for concentrating, in the substantial absence of
gel formation, a solution of a halogenated aromatic polyester wherein the
solvent thereof has a boiling point below the decomposition temperature of
the polymer and having the recurring structural formula:
##STR4##
where X which may be the same or different is chlorine or bromine, Y which
may be the same or different is hydrogen, chlorine or bromine, R and R'
may be the same or different and represent lower alkyl groups, hydrogen,
or together constitute a cyclic hydrocarbon group, and n equals at least
10, having an initial polymer concentration of from about 3 to about 25%
by weight comprising:
(a) heating the polymer solution to a temperature of not less than the
temperature at which the solvent thereof evaporates in the evaporation
zone of (b), which temperature is in the range of from about 20.degree. to
about 300.degree. C., by passing the solution through a heating zone;
(b) passing the heated polymer solution of (a) from the heating zone
through at least one orifice located in an evaporation zone, said
evaporation zone containing prior to passage of the polymer solution
therein a saturated atmosphere of the vapor of the solvent of the polymer
solution at a temperature not greater than the temperature of the polymer
solution after it exits the heating zone and not greater than the boiling
point of the vapor at the pressure present within the evaporation zone; to
thereby produce a polymer solution having a final concentration of from
about 8 to about 60% by weight polymer, based upon the total weight of the
polymer solution; and
(c) optionally admixing a part of said concentrated polymer solution of (b)
with the unconcentrated polymer solution of (a) prior to passage of the
resulting mixture through the heating zone.
8. The process of claim 7 wherein the halogenated aromatic polyester is
dissolved in a solvent selected from the group consisting of methylene
chloride, chloroform, tetrachloroethane, trichloroethane, chlorobenzene,
chlorotoluene, dichloroethane, benzene, toluene, xylene and mixtures
thereof.
9. The process of claim 8 wherein the polymer solution is heated to a
temperature at about 50.degree. to about 190.degree. C., the temperature
of the solvent vapor in the evaporation zone is the boiling point of the
solvent, and the pressure within the evaporation zone is atmospheric.
10. The process of claim 7 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrabromobisphenol A and
a mixture of about 45 to 75% by weight isophthaloyl chloride and
correspondingly about 55 to about 25% by weight terephthaloyl chloride.
11. The process of claim 7 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrabromobisphenol A and
a mixture of about 60% by weight isophthaloyl chloride and correspondingly
about 40% by weight terephthaloyl chloride.
12. The process of claim 7 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrachlorobisphenol A
and a mixture of about 90 to about 40% by weight isophthaloyl chloride and
correspondingly about 10 to about 40% by weight terephthaloyl chloride.
13. The process of claim 7 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrachlorobisphenol A
and a mixture of about 70% by weight isophthaloyl chloride and
correspondingly about 30% by weight terephthaloyl chloride.
14. The process of claim 7 wherein R and R' may contain from 1 to 5 carbon
atoms and wherein n may be from about 40 to about 400.
15. A continuous process for concentrating, in the substantial absence of
gel formation, a solution of a halogenated aromatic polyester of the
recurring structural formula:
##STR5##
where X may be the same or different is chlorine or bromine, Y which may
be the same or different is hydrogen, chlorine or bromine, R and R' may be
the same or different and represent lower alkyl groups, hydrogen, or
together constitute a cyclic hydrocarbon group, and n equals at least 10,
dissolved in methylene chloride and having an initial polymer
concentration of from about 3 to about 25% by weight comprising:
(a) heating the polymer solution to a temperature at which the solvent
evaporates in the evaporation zone of (b) of from about 38.5.degree. to
about 200.degree. C. by passing the solution through a heating zone; and
(b) passing the heated polymer solution of (a) through at least one orifice
located in an evaporation zone, said evaporation zone containing prior to
passage of the polymer solution therein a saturated atmosphere of
methylene chloride vapor at a temperature of from about 20.degree. to
about 60.degree. C., said evaporation zone having a means for regulating
the pressure therein in a manner sufficient to achieve the selected
solvent vapor temperature to produce a solution of the halogenated
aromatic polyester having a final concentration of from about 15 to about
30%, by weight polymer, based upon the total weight of the polymer
solution.
16. The process of claim 15 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrabromobisphenol A and
a mixture of about 45 to about 75% by weight isophthaloyl chloride and
correspondingly about 55 to about 25% by weight terephthaloyl chloride.
17. The process of claim 15 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrabromobisphenol A and
a mixture of about 60% by weight isophthaloyl chloride and correspondingly
about 40% by weight terephthaloyl chloride.
18. The process of claim 15 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrachlorobisphenol A
and a mixture of about 90 to about 40% by weight isophthaloyl chloride and
correspondingly about 10 to about 40% by weight terephthaloyl chloride.
19. The process of claim 15 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrachlorobisphenol A
and a mixture of about 70% by weight isophthaloyl chloride and
correspondingly about 30% by weight terephthaloyl chloride.
20. The process of claim 15 wherein R and R' may contain from 1 to about 5
carbon atoms and wherein n may be from about 40 to about 400.
21. The process of claim 15 wherein part of the concentrated solution of
the halogenated aromatic polyester solution of (b) is mixed with the
unconcentrated solution of (a), prior to passage of said mixture through
the heating zone.
22. A continuous process for concentrating, in the substantial absence of
gel formation, a solution of a halogenated aromatic polyester of the
recurring structural formula:
##STR6##
where X which may be the same or different is chlorine or bromine, Y which
may be the same or different is hydrogen, chlorine or bromine, R and R'
may be the same or different and represent lower alkyl groups, hydrogen,
or together constitute a cyclic hydrocarbon group, and n equals at least
10, dissolved in methylene chloride having an initial polymer
concentration from about 3 to about 25% by weight comprising:
(a) heating the polymer solution to a temperature at which the solvent
evaporates in the evaporation zone of (b) of from about 38.5.degree. to
about 200.degree. C. by passing the solution through a heating zone; and
(b) passing the heated polymer solution of (a) through at least one orifice
located in an evaporation zone, said evaporation zone containing prior to
passage of the polymer solution therein a saturated atmosphere of
methylene chloride vapor at atmospheric pressure and at a temperature of
the boiling point of the solvent, and having an exit orifice for said
vapor, to produce a polymer solution having a final polymer concentration
of from about 15 to about 30%, by weight, based upon the total weight of
the polymer solution.
23. The process of claim 22 wherein the polymer solution of (a) is heated
to a temperature of about 50.degree. to about 190.degree. C.
24. The process of claim 14 wherein the polymer solution of (a) is heated
to a temperature of about 170.degree. to about 190.degree. C.
25. The process of claim 22 wherein said halogenated aromatic polyester of
the recurring structural formula is the product of tetrabromobisphenol A
and a mixture of about 45 to about 75% by weight isophthaloyl chloride and
correspondingly about 55 to about 25% by weight terephthaloyl chloride.
26. The process of claim 22 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrabromobisphenol A and
a mixture of about 60% by weight isophthaloyl chloride and correspondingly
about 40% by weight terephthaloyl chloride.
27. The process of claim 22 wherein said halogenated aromatic polyester of
the recurring strctural formula is a product of tetrachlorobosphenol A and
a mixture of about 90 to about 40% by weight isophthaloyl chloride and
correspondingly about 10 to 40% by weight terephthaloyl chloride.
28. The process of claim 22 wherein said halogenated aromatic polyester of
the recurring structural formula is a product of tetrachlorobisphenol A
and a mixture of about 70% by weight isophthaloyl chloride and
correspondingly about 30% by weight terephthaloyl chloride.
29. The process of claim 22 wherein R and R' may contain from 1 to about 5
carbon atoms and wherein n may be from about 40 to about 400.
30. The process of claim 22 wherein part of the concentrated solution of
the halogenated aromatic polyester solution of (b) is mixed with the
unconcentrated solution of (a) prior to passage of said mixture through
the heating zone.
31. A continuous process for concentrating, in the substantial absence of
gel formation, a solution of the condensation product of
tetrabromobisphenol A with a mixture of from about 55 to about 25% by
weight terephthaloyl chloride and from about 45 to about 75% by weight
isophthaloyl chloride dissolved in methylene chloride, said solution
having an initial polymer concentration of from about 7 to about 15% by
weight, said process comprising:
(a) heating the polymer solution to a temperature of from about 50.degree.
to about 190.degree. C. by passing the solution through a heating zone;
(b) passing the heated polymer solution of (a) through at least one orifice
located in an evaporation zone, said evaporation zone containing prior to
passage of the polymer solution therein a saturated atmosphere of
methylene chloride vapor at atmospheric pressure at a temperature of the
boiling point of the solvent, and having an exit orifice for said vapor,
to produce a polymer solution having a final polymer concentration of from
about 19 to about 22%, by weight, based upon the total weight of the
polymer solution; and
(c) admixing part of said concentrated polymer solution of (b) with the
unconcentrated polymer solution of (a) prior to passage of the resulting
mixture through the heating zone.
32. The process of claim 7 wherein the temperature of the vapor in the
evaporation zone is from about 10.degree. to about 200.degree. C. less
than the temperature of the heated polymer solution of (a). |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
Typically, when a polymer is prepared by techniques such as solution
polymerization, it is present in relatively dilute concentrations for ease
of handling. Subsequent processing techniques to which the polymer
solution will eventually be subjected such as dry-spinning, however,
necessitate that the polymer be concentrated.
For example, when halogenated aromatic polyesters, such as the condensation
products of 4,4'-isopropylidene-2,2', 6,6'-tetrachlorodiphenol or
4,4'-isopropylidene-2,2',6,6'-tetrabromodiphenol with isophthalic acid
and/or terephthalic acid or the ester forming derivatives thereof, are
prepared by the solution polymerization technique as described, for
example, in U.S. Pat. No. 3,234,167, and as described herein, the final
polymer solution after neutralization and removal of the acid acceptor,
contains approximately 10% by weight polymer and about 3 to 5%, by weight,
water in methylene chloride. This solution is too dilute for direct
spinning so the polymer solution must be concentrated to about 20%, by
weight, polymer.
A continuous method for neutralizing excess tertiary amine acid acceptor is
disclosed in U.S. Pat. No. 4,322,521, entitled "Improved Process for
Producing Halogenated Aromatic Polyesters," by Albert G. Williams. A
continuous countercurrent extraction method for removing tertiary amine
hydrochloride from the polymer solution is disclosed in U.S. Pat. No.
4,360,662, entitled "Continuous Countercurrent Extraction Process for
Removing Water-Soluble Impurities From Water Immiscible Polymer Solutions"
and filed concurrently herewith, by Albert G. Williams. The disclosures of
each of the above-identified patent applications are hereby incorporated
by reference.
It would be advantageous to develop a continuous method for concentrating
halogenated aromatic polyester solutions, and polymer solutions generally,
so that the entire process for preparing such polymer solutions from
polymerization through spinning could be carried out on a continuous basis
and in a manner sufficient to avoid the cost of precipitation, drying,
solvent recovery and handling thereof.
One problem involved in attempting to concentrate a polymer solution, such
as a 10% polymer solution of a halogenated aromatic polyester, to a more
concentrated solution, such as a 20% solution, is the formation of polymer
gels or "skins" on the surface of the polymer due to the poor
diffusion/evaporation balance which exists therein. Also, such a polymer
solution has a high viscosity (a 10% solution has a viscosity of from
about 50 to about 100 poise, and a 20% polymer solution has a viscosity of
from about 1000 to about 3000 poise) and notoriously low heat transfer
coefficients thereby requiring large equipment and high capital outlay.
The search has continued for continuous methods for concentrating a polymer
solution while avoiding the above-discussed problems of the prior art. The
present invention was made as a result of this search.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, a general object of the present invention is to avoid or
substantially alleviate the above problems of the prior art.
A more specific object of the present invention is to provide a process for
concentrating a polymer solution so that the concentrated polymer solution
might be useful for the direct spinning of a fiber.
Another object of the present invention is to provide a process for
concentrating a polymer solution without the formation of polymer gels or
skins.
Still another object of the present invention is to provide a continuous
process for concentrating a solution of halogenated aromatic polyester so
that the entire process from polymerization through spinning might be
carried out on a continuous and economically efficient basis.
Other objects and advantages of the invention will become apparent from the
following summary and description of the preferred embodiments of the
present invention.
The present invention provides a continuous process for concentrating and
reducing polymer gel formation of a polymer solution wherein the solvent
thereof has a boiling point below the decomposition temperature of the
polymer comprising:
(a) heating the polymer solution to a temperature of not less than the
temperature at which the solvent thereof evaporates in the evaporation
zone of (b) by passing the solution through a heating zone;
(b) passing the heated polymer solution of (a) from the heating zone
through at least one orifice located in an evaporation zone, said
evaporation zone containing a saturated atmosphere of the vapor of the
solvent of the polymer solution at a temperature of not greater than the
temperature of the polymer solution after it exits the heating zone and
not greater than the boiling point of the vapor at the pressure present
within the evaporation zone; and
(c) optionally admixing a part of said concentrated polymer solution of (b)
with the unconcentrated polymer solution of (a) prior to passage of the
resulting mixture through the heating zone.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a schematic presentation of an apparatus arrangement capable
of carrying out the process of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is directed to a process for concentrating polymer
solutions. The initial concentration of the polymer solution will, from a
practical standpoint, generally depend on the particular method used to
prepare the polymer and can therefore vary within a wide range of possible
concentrations. A typical polymerization technique which results in a
solution of the polymer includes the solution polymerization method.
Alternatively, one may wish to dissolve a solid polymer in excess solvent
to form a dilute solution which is subsequently concentrated, since the
more concentrated the solution prepared directly from a solid polymer, the
more difficult if is to dissolve the polymer.
Regardless of the source of the polymer solution the present invention can
be employed to increase the concentration of any polymer dissolved in a
suitable solvent which has a boiling point below the decomposition
temperature of the polymer.
The final concentration to which the polymer solution is raised will depend
on the processing techniques to which the polymer solution will be
subjected.
For example, when the polymer solution is to be directly spun into fibers
the final concentration will be selected in such a manner that the overall
balance of polymer solution properties renders it suitable for such
techniques. For fiber spinning, such factors as solvent identity and
intrinsic viscosity of the polymer, will affect the selection of the final
concentration of the polymer solution. For instance, as the intrinsic
viscosity of the polymer increases, the target concentration to which the
polymer solution is adjusted will decrease. Conversely, as the intrinsic
viscosity of the polymer decreases the target concentration of the polymer
solution will increase. The intrinsic viscosity of the polymer cannot be
too low, however, otherwise the fiber properties would suffer.
The above discussion is provided merely to illustrate that there may be
many factors which interact in selecting the target polymer concentration
and that the present invention can be employed to achieve whatever
increased concentration is finally selected relative to the initial
concentration.
Subject to the above considerations the polymer solutions which can be
concentrated by the present invention will generally have the polymer
dissolved therein at an initial concentration of generally from about 5 to
about 50, typically from about 3 to about 25, and preferably from about 2
to about 15%, by weight, based on the weight of the polymer solution.
Correspondingly, the polymer will be present in the final concentrated
polymer solution in an amount of from about 8 to about 60, typically from
about 10 to about 40, and most preferably from about 15 to about 30%, by
weight, based on the weight of the polymer solution.
When the polymer is the halogenated aromatic polyester of the type
described herein and the solvent is methylene chloride, the final polymer
concentration will be selected for purposes of dry-spinning to be from
about 15 to about 30, typically from about 17 to about 27, and preferably
from about 18 to about 25%, by weight, based on the weight of the polymer
solution.
When the polymer is the condensation product of tetrabromobisphenol A and
from about 45 to about 75% by weight isophthaloyl chloride and
correspondingly from about 55 to about 25% by weight terephthaloyl
chloride having an intrinsic viscosity of about 1.2 dl/gm. as determined
from a 0.1% (w/w) mixture of phenol/trichlorophenol and the solvent is
methylene chloride, the preferred final polymer solution concentration for
purposes of dry-spinning is between about 19 and about 22%, (e.g., about
20 and about 21%), by weight, thereof.
Representative examples of polymer solutions which may be concentrated by
the present invention include cellulose acetate polymer dissolved in
acetone or a mixture of acetone and water, cellulose triacetate polymer
dissolved in methylene chloride or a mixture of methylene chloride and
methanol, polyacrylonitrile dissolved in dimethyl formamide or dimethyl
acetamide, and polyvinyl chloride/vinylidene chloride dissolved in
acetone.
The present invention is particularly useful in concentrating halogenated
aromatic polyester solutions.
Preferred halogenated aromatic polyesters have recurring units of the
structural formula:
##STR1##
wherein X, which may be the same or different, may be chlorine or bromine,
Y, which may be the same or different, may be hydrogen, chlorine, or
bromine, R and R' may be the same or different and represent lower alkyl
groups (e.g., having from 1 to about 5 carbon atoms), hydrogen, or
together constitute a cyclic hydrocarbon group, and n equals at least 10
(e.g., n equals about 40 to 400, typically about 50). Commonly the
aromatic polyester utilized in accordance with the process of this
invention has a chlorine and/or bromine content of about 15 to about 60%,
by weight, based upon the weight of the aromatic polyester (e.g., a
chlorine and/or bromine content of about 25 to 50% by weight). As is
apparent from the structural formula, the aromatic polyester is
chlorinated and/or brominated in the sense that these substituents are
directly attached to an aromatic ring. Preferably the halogen substituents
are all bromine.
The halogenated aromatic polyesters conforming to the above-defined formula
are prepared by reacting substantially equimolar amounts of (1) an
appropriate bisphenol, and (2) a diacid halide such as isophthaloyl
chloride, terephthaloyl chloride, or mixtures thereof by solution
polymerization.
Initially the appropriate bisphenol is dissolved in a suitable solvent. The
catalyst or acid acceptor is also dissolved in the solvent prior to the
addition of the diacid halide.
The bisphenols which are useful in the preparation of the polyesters having
recurring units of the formula illustrated above have the structure:
##STR2##
where X, Y, R and R' have the same significance as set forth hereinabove.
Suitable bisphenols which are useful in the practice of this invention
include bis(3,5-dibromo-4-hydroxyphenyl)methane;
bis(3,5-dichloro-4-hydroxyphenyl)methane;
bis(3-chloro-5-bromo-4-hydroxyphenyl)methane;
1,1-bis(3,5-dibromo-4-hydroxyphenyl)ethane;
1,1-bis-(3,5-dichloro-4-hydroxyphenyl)ethane;
1,1-bis-(3-chloro-5-bromo-4-hydroxyphenyl)ethane;
1,1-bis-(3,5-dibromo-4-hydroxyphenyl)propane;
1,1-bis-(3,5-dichloro-4-hydroxyphenyl)propane;
1,1-bis-(3-chloro-5-bromo-4-hydroxyphenyl)propane;
2,2-bis-(3,5-dibromo-4-hydroxyphenyl)propane;
2,2-bis-(3,5-dichloro-4-hydroxyphenyl)propane;
2,2-bis-(3-chloro-5-bromo-4-hydroxyphenyl)-propane;
bis-(3-bromo-4-hydroxyphenyl)methane;
bis-(3-chloro-4-hydroxyphenyl)methane;
3-bromo-3'-chloro-bis(4-hydroxyphenyl)-methane;
1,1-bis-(3-bromo-4-hydroxyphenyl)ethane;
1,1-bis-(3-chloro-4-hydroxylphenyl)ethane;
3-bromo-3'-chloro-bis-(4,4'-hydroxyphenyl)ethane;
1,1'-bis-(3-bromo-4-hydroxyphenyl)-propane;
1,1'-bis(3-chloro-4-hydroxyphenyl)propane;
1,1'-(3-chloro-3'-bromo-bis-[4,4'-hydroxyphenyl])propane;
2,2'-bis(3-bromo-4-hydroxyphenyl)propane; 2,2'-bis-(3-chloro-
4-hydroxyphenyl)propane;
2,2'-(3-bromo-3'-chloro-bis[4,4'-hydroxyphenyl])-propane; as well as their
alkali metal salts.
Preferred bisphenols are 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)propane, also
known as tetrabromobisphenol A, and
2,2-bis-(3,5-dichloro-4-hydroxyphenyl)propane, also known as
tetrachlorobisphenol A.
Many brominated bisphenols of the above-described structure are
commercially available and may be prepared by the condensation of a lower
alkyl ketone or aldehyde with two molecules of the phenol and subsequently
brominating and/or chlorinating the unsubstituted phenol. This reaction is
usually carried out with or without an inert solvent in the presence of an
acid. This reaction is summarized in the case of X and Y being bromine in
the following equations wherein R and R' have the meanings hereinabove
described.
##STR3##
The solvent in which the bisphenol and catalyst or acid acceptor are
dissolved and in which the reaction takes place should be inert and
incapable of reacting with any of the components present therein.
Furthermore, the solvent should be a solvent for both the starting
materials as well as the resulting polymer. This allows the solvent to
help maintain the forming polymer in a more workable form.
Suitable solvents which may be utilized in the solution polymerization
technique described herein include chloroalkanes and aromatic and
chloroaromatic compounds. Examples of such compounds include methylene
chloride, chloroform, tetrachloroethane, trichloroethane, chlorobenzene,
chlorotoluene, dichloroethane, benzene, toluene, and xylene.
The catalyst or acid acceptor is preferably a tertiary amine which is
capable of undergoing a reaction with the bisphenol to form a complex
salt. The bisphenol complex salt subsequently reacts with the daicid
halide and liberates an amine halide.
Stoichiometric amounts of the bisphenol and the catalyst would require a
ratio of the tertiary amine to the bisphenol of about 2:1. However, it has
been found that in order for the reaction to proceed at a commercially
acceptable rate, an excess of acid acceptor should be employed. The amount
of excess acid acceptor is generally less than about 50, typically less
than about 20, and preferably less that about 5%, by weight, based upon
the stoichiometric amount of acid acceptor required. The upper limit of
acid acceptor is not critical. However, it should be remembered that
excess amounts of acid acceptor must be neutralized and the reaction
product of the neutralization reaction must be separated from the final
polymer product.
Representative examples of suitable tertiary amine catalysts or acid
acceptors include triethylamine, diamino-2,2,2,bicyclo octane, tripropyl
amine, dimethyl aniline, pyridine, dimethyl and benzyl amine.
Triethylamine is a preferred acid acceptor.
It will be noted that halogenated aromatic polyesters are prepared by the
condensation of bisphenols with the diacid halides of isophthalic acid,
terephthalic acid or mixtures thereof. The use of a diacid halide as
opposed to other corresponding derivatives is critical, the direct
preparation of polymers from bisphenols and free acids being normally not
possible. These acid halides may be derived from the corresponding
dicarboxylic acid by any one of several methods well known in the art such
as by reacting the respective acids with thionyl chloride. Thus, the
diacid halide is preferably utilized in the form of a diacid chloride.
It is generally preferred to dissolve the diacid halide in the same type of
solvent utilized to prepare the solution containing the halogenated
bisphenol. Although this is not critical, the employment of a solvent
provides for a more accurate control of the addition of the diacid halide
to the bisphenol containing solution.
In preparing a preferred brominated aromatic polyester, the diacid halide
will generally be utilized in the form of an aromatic acid chloride
mixture of from about 45 to about 75% (e.g., 60%) by weight isophthaloyl
chloride and correspondingly from about 55 to about 25% (e.g., 40%) by
weight terephthaloyl chloride.
In preparing a preferred chlorinated aromatic polyester, the diacid halide
will generally be utilized as an aromatic acid chloride mixture of from
about 90 to about 40%, and preferably from about 80 to about 60% (e.g.,
70%) by weight isophthaloyl chloride and correspondingly from about 10 to
about 60% and preferably from about 20 to about 40% (e.g., 30%) by weight
terephthaloyl chloride.
For smooth operation in a stirred solution, the resulting polymer product
preferably should be about 10% or less on the basis of the total weight of
the solvent although percentages as high as 25% may be utilized depending
upon the molecular weights of the polymer.
Generally substantially stoichiometric amounts of each reactant are
employed. Typical molar amounts of from about 1:0.9:0.1 to about
1:0.4:0.6, of the ratio of bisphenol, isophthaloyl chloride, and
terephthaloyl chloride, respectively, may be utilized when preparing a
chlorinated aromatic polyester. Typical molar amounts of from about
1:0.45:0.55 to about 1:0.75:0.25 of the ratio of bisphenol, isophthaloyl
chloride, and terephthaloyl chloride, respectively, may also be utilized
when preparing a brominated aromatic polyester.
Polymerization of the halogenated aromatic polyesters may be carried out in
a batch, semi-continuous, or continuous manner, as desired. However, the
polymerization reaction is preferably carried out in a continuous manner,
by which the reactants are continuously introduced into the reaction zone
and the polymer product is continuously prepared and withdrawn. This may
be achieved, for example, by utilizing a cylindrical tube, having static
mixers as a reaction vessel. The bisphenol containing solution is passed
through the tube while adding the diacid halide at various points along
the longitudinal axis of the tube. Thus, the diacid halide is added in
large amounts at the upstream portion of the tube and in gradually
decreasing amounts at positions further downstream in the tube.
The final concentration of the polymer in solution is from about 3 to about
25, typically from about 5 to about 20 and preferably from about 7 to
about 15% by weight of the total reaction mixture. At these
concentrations, the solution viscosity will generally vary from about 1 to
about 3000 poise, typically from about 5 to about 2000 poise, and
preferably from about 10 to about 1000 poise.
Polymerization is effected at temperatures which may vary from about 0 to
about 200, typically from about 10 to about 100, and preferably from about
15.degree. to about 50.degree. C., and at corresponding autogenous
pressures which are due to the vapor pressure of the solvent at the
aforenoted temperatures which may vary from about 0.2 to about 26,
typically from about 0.3 to about 4.8, and preferably from about 0.4 to
about 1.4, atmospheres.
Agitation of the reactants should be sufficient to evenly disperse the
diacid halide throughout the bisphenol containing solution to avoid a
build-up of the concentration of the diacid halide in a localized area
within the reaction mixture. Such agitation may be supplied by any of the
standard means of mixing such as by stirrer, shaker, static mixer, spray
nozzle or other flow agitating systems.
The present process typically employs reaction times of generally from
about 0.1 to about 20, typically from about 1 to about 10, and preferably
from about 2 to about 6, hours when conducted on a batch basis.
Polymerization conducted on a continuous basis will typically employ
shorter polymerization times depending on the degree of mixing.
After polymerization, the polymer may be recovered by admixing with the
polymer containing solution either an aqueous solution of hydrochloric
acid, or, in a preferred embodiment, gaseous, substantially anhydrous,
hydrogen chloride to neutralize the excess acid acceptor. The use of
gaseous, substantially anhydrous, hydrogen chloride to neutralize the acid
acceptor is disclosed in U.S. Pat. No. 4,322,521, entitled "Improved
Process for Producing Halogenated Aromatic Polyesters" by Albert G.
Williams.
The amount of hydrogen chloride added to the polymer containing solution
should be sufficient to completely neutralize the excess, uncombined
tertiary amine and thus is dependent upon the amount of excess tertiary
amine initially added. The gaseous hydrogen chloride may be added to the
polymer containing solution by any means known to those skilled in the
art. For example, the gaseous hydrogen chloride may be added using a gas
sparge.
Reaction of the hydrogen chloride with the tertiary amine to form a
tertiary amine hydrochloride takes place substantially immediately (i.e.,
as soon as the hydrogen chloride gas is dissolved in the polymer
containing solution). This rapid neutralization of the tertiary amine is
commercially advantageous since other neutralization methods, which
involve the addition of aqueous hydrochloric acid, require much longer
neutralization times because of the existence of a two-phase system. To
some extent, the long neutralization times involved when an aqueous
solution is employed, can be remedied by adding a large excess of hydrogen
chloride, but this is disadvantageous because (1) it introduces further
impurities (the excess hydrogen chloride) into the polymer containing
solvent, and (2) the addition of more aqueous hydrochloric acid involves
the further dilution of the tertiary amine hydrochloride product and makes
this product more difficult to recover.
Besides the time advantages resulting from the use of gaseous,
substantially anhydrous, hydrogen chloride instead of an aqueous solution
of hydrochloric acid, there is the further advantage that much smaller
amounts of hydrogen chloride may be introduced into the reaction system
when the anhydrous method is employed. Thus, there is less waste of
hydrogen chloride as well as reduced environmental dangers.
The gaseous hydrogen chloride should be substantially anhydrous. Small
amounts of water may be introduced into the system but, to the extent
water is introduced, one encounters to that extent the various problems
described hereinabove.
After neutralization of the tertiary amine, with hydrogen chloride, the
resulting tertiary amine hydrochloride is removed from the polymer
containing solution. This may be accomplished by multiple batch extraction
with water or by employing the continuous countercurrent extraction method
disclosed in U.S. Pat. No. 4,360,662, entitled "Continuous Countercurrent
Extraction Process for Removing Water Soluble Impurities From Water
Immiscible Polymer Solutions", by Albert G. Williams. The disclosure of
this patent application is hereby incorporated by reference.
After removal of the water-soluble impurities, the halogenated aromatic
polyester is concentrated without isolation by the flash evaporation
process described herein and thereafter processed for shaping, e.g., spun
or cast for making fibers or film respectively.
The continuous process for concentrating a polymer solution of the present
invention is discussed with reference to the figure.
The first step in the process comprises passing the polymer solution
through conduit (11) to heating zone (12) to heat the polymer solution.
The temperature of this heating zone is dependent in part on the identity
of the solvent which is present in the polymer solution. Such temperatures
are selected in a manner sufficient to heat the polymer solution to not
less than the temperature at which the solvent evaporates at a given
pressure present within the evaporation chamber into which it is
subsequently introduced. The evaporation step relies on the mechanism
wherein the energy absorbed by the polymer solution during the heating
step is preserved by maintaining a back pressure on the polymer solution
to prevent vaporization of the solvent in conduit (13), and is
subsequently released in the evaporation chamber causing evaporation of
the solvent. Consequently, the greater the temperature differential
between the heated polymer solution and the solvent vapor in the
evaporation chamber (which is at a temperature of at least its boiling
point at a given pressure), the faster will be the rate of evaporation.
The temperatures to which the polymer solution is heated will vary from
about 20 to about 300, typically from about 35 to about 290 and preferably
from about 50.degree. to about 190.degree. C.
When the polymer solvent is methylene chloride and the polymer is a
halogenated aromat | | |
