PROCESS FOR FRACT1ONATION/CONCENTRATION
TO REDUCE THE POLYDISPERS1V1TY OF POLYMERS
BACKGROUND OF THE INVENTION
The present disclosure is directed to methods for reducing the levels of cyclic
oligomers produced during the formation of polyetherimide resins. More particularly,
a fast and efficient fractionation method is disclosed to reduce the polydispersivity of
the polyetherimide resins without having to precipitate the desired polyetherimide in
solid form. Another aspect of this invention is to concentrate cyclic oligomers for
further use in other applications.
Polymerization reactions typically lead to products of varying polydispersivity or
polydispersity, i.e.. having a range of components from low to high molecular weight.
The quality of a final polymeric product depends to a large extent on how broad its
molecular weight distribution is (in most cases, the broader the distribution, the lower
the quality). Polydispersivity is expressed as the polydispersivity index (PDI), which
is the ratio of the weight average molecular weight (Mw) to the number average
molecular weight (Mn).
In many polymerization reactions, undesirable low molecular weight by-products and
unreacted monomers remain in the final product. Such by-products and unreacted
monomers can have adverse effects on the properties of the desired polymers and thus
must be separated.
For example, aromatic polyethers, particularly polyetherimides, are important
engineering resins because of their excellent properties. These polymers may be
produced by various methods including the condensation polymerization of a diamine
and a dianhydride as in the reaction of m-phenylene diamine (mPD) and bisphenol-A
dianhydride (BPADA). The resulting polyetherimides have a polydispersivity of
about 2.2.
Alternatively, polyelherimides may be prepared by a displacement polymerization
process which reacts salts of dihydroxyaromatic compounds, such as bisphenol A
disodium salt (BPA.N32), with dihaloaromatic molecules. For example,
polyetherimides are conveniently prepared by the reaction of salts of
dihydroxyaromatic compounds with bis(halophthalimides) as illustrated by l,3-bis[N-
(4-chlorophthalimido)]benzene (hereinafter sometimes "CIPAMI"), which has the
structure
The bis(halophthalimides), in turn, are produced by reacting at least one diamino
compound, preferably an aromatic diamine such as mPD or p-phenylenediamine
(pPD), and at least one halophthalic anhydride.
According (o U.S. Pat. Nos. 5,229,482 and 5,830,974, the preparation of aromatic
polycthers may be conducted in solution in relatively non-polar solvents, using a
phase transfer catalyst which is substantially stable under the temperature conditions
employed. Solvents disclosed in U.S. Pat. No. 5,229,482 include o-dichlorobenzene,
dichlorotoluene, 1,2,4-trichlorobenzene and diphenyl sulfone. In U.S. Pat. No.
5,830,974, monoalkoxybenzenes such as anisole, diphenylether, or phenetole are
employed. Solvents of the same types may be used for the preparation of the
bis(halophthalimide) intermediates.
The general scheme for the production of bis(halophthalimide) and the subsequent
production of polyetherimide is set forth in Figure 1. The polyetherimides produced
by these displacement polymerizations have a relatively high polydispersivity,
ranging from about 3.6 to about 2.6, depending upon the amount of 3-C1PA and 4-
CIPA used in preparing (he C1PAM1 monomer. Polymers made by these methods can
have between about 10% and about 15% of a cyclic monomer by-product.
When bisphenol A, mPD and 4-CIPA are used to produce polyetherimides, it has been
found that the level of cyclic oligomers in the final product is about 3%. However, it
has been found that the amount of cyclics increases as the level of 3-C1PA is
increased as a starting material in C1PAMI synthesis. Where 100% 3-C1PA and mPD
are used as the starling material, the amount of cyclic oligomers can range from about
1 5% to about 20%. Interestingly, it has been found that about two thirds of the cyclic
oligomers are a single 1:1 adduct. The reaction scheme demonstrating the use of 3-
C1PAM1 to produce a polyetherimide with the cyclic oligomer by-product is set forth
in Figure 2.
Other undesirable by-products include short polymer chains and linear oligomers.
These by-products, in addition to unreacted monomers, being off specification, must
be discarded after separation, increasing the cost and size of the waste stream and
reducing the efficiency of the process.
High levels of these low molecular weight species can also have adverse effects on
the properties of the resulting polymer. Such negative effects include a lower glass
transition temperature (Tg), reduced ductility, and problems with processing including
surface appearance, as demonstrated by reduced glossiness.
However, it has also been found that the use of 3-C1PA in combination with other
bisphenols and diamines can produce polyetherimides possessing higher Tg (about
15° to about 20° C higher), and improved flow at high shear. It is therefore desirable
to use 3-C1PA as a starting material, at least in part, in the production of
polyetherimides
Means for recovering products from polymerization reactions are known. For
example, polymer fractionation processes recover a desired polymer in solid form
from a solution by precipitation into an anti-solvent. The process is referred to as
total precipitation if the anti-solvent does not dissolve the polymer or low molecular
weight species in the polymer such as linear oligomers, cyclic oligomers and
monomers. Heptane and other alkanes are examples of anti-solvents which may be
used for total precipitation of polymers, especially polyetherimide polymers.
However, where such anti-solvents are used, the presence of low molecular weight
species in the polymer such as linear oligomers, cyclic oligomers and monomers will
result in a product having a higher polydispersivity.
Other methods for recovering polyetherimide polymers include the precipitation of
highly polydispersive polymers in toluene, acetone, or tetrahydrofuran, which
dissolve low molecular weight species and unreacted monomers from the polymer.
Thus, polymers obtained by these methods have reduced polydispersivity.
It is desirable, therefore, to develop a method for preparing polymers which is adapted
to the close control of molecular weight and removing unreacted monomers and
undesirable by-products by relatively simple means. In the case of polyetherimide
polymers, polymers with lower polydispersivily will have improved
thermomechanical performance characteristics.
BRIEF DESCRIPTION OF THE INVENTION
The present disclosure is directed to methods for reducing the polydispersivity of a
polymer by:
forming a polymer solution;
contacting the polymer solution with an anti-solvent capable of dissolving low
molecular weight species but not the desired high molecular weight polymer;
allowing phase separation to occur to obtain a light phase and a heavy phase; and
recovering the desired polymer from the heavy phase,
wherein the resulting polymer has reduced polydispersivity.In one embodiment, the
method of the present disclosure includes concentrating and recovering the cyclic and
low molecular weight linear oligomers in the light phase.
In another of its aspects, the present disclosure includes methods for reducing the
polydispersivity of a polyetherimide resin that include:
forming a polyetherimide solution;
contacting the polyetherimide solution with an anti-solvent capable of dissolving low
molecular weight species but not the high molecular weight polyetherimide;
allowing phase separation to occur to obtain a light phase and a heavy phase; and
recovering the desired polyetherimide from the heavy phase,
wherein the resulting polyetherimide has reduced polydispersivity.
Another aspect of the present disclosure is to polyetherimide resins with lower
polydispersivity produced in accordance with the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an overview of the CIPAMI and polyetherimide synthesis process.
FIG. 2 is a depiction of CIPAMI synthesis demonstrating undesirable cyclic
formation.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present disclosure, methods have been developed which lower
the polydispersivity of polymers by removing undesirable by-products and unreacted
monomers from a polymer solution. The methods of the present disclosure utilize
fractionation of a polymer solution with an anti-solvent to remove low molecular
weight by-products and unreacted monomers. The anti-solvent, which is preferably
admixed with a certain fraction of the polymer solvent, dissolves low molecular
weight by-products and unreacted monomers, which enter a light phase, but does not
dissolve the polymer, which remains in the heavy phase. Thus, once the two phases
arc obtained, simple phase separation techniques may be utilized to obtain a heavy
phase containing the desired polymer, without the need for precipitation, filtration,
washing, etc. that is otherwise required to separate the desired polymer from the
undesirable by-products and monomers. The resulting polymer, having had the
undesirable low molecular weight by-products and unreacted monomers removed, has
a lower polydispersivity.
In one embodiment, the methods of the present disclosure can be used in the synthesis
of polyetherimides produced from bisimide monomers which, in turn, are prepared
from phthalic anhydrides and diamines. The lower polydispersivity can be achieved
by removing low molecular weight species such as short polymer chains, linear
oligomers and cyclic oligomers from the desired polymer. While the following
disclosure utilizes the preparation of polyetherimides as an example, the methods of
the present disclosure may be utilized to reduce the polydispersivity of any polymer
placed in solution with an appropriate polymer solvent and anti-solvent pair.
Anhydrides suitable for use in preparing the bishalophthalimides of the present
invention have formula (II)
wherein X is a moiety which may be any organic group that does not interfere with
the imidizalion reaction. In one embodiment X is a displaceable group which
participates, in a subsequent polymerization reaction. Preferably, X is nitro, nitroso,
tosyloxy (-OTs) or halogen; most preferably X is chlorine. Especially preferred
anhydrides include 3-chlorophthaltc anhydride, 4-chlorophthalic anhydride, and
dichlorophthalic anhydride. In a most preferred embodiment, the bis-halophthalimide
monomer is made from either substantially pure 3-CIPA or a mixture of 3-C1PA
combined with other phthalic anhydride monomers selected from the group consisting
of 4-chlorophthalic anhydride, dichlorophthalic anhydride, and substituted analogs
thereof where the other positions on the aromatic ring of the anhydride are either
hydrogen atoms or substituted with nonreactive groups such as alky! or aryl groups,
and mixtures thereof.
In addition, in one embodiment of the present disclosure, phthalic anhydride (i.e., a
compound having the structure of formula (11) wherein X is hydrogen) may be
separately added to the reaction mixture. In such a case, the addition of phthalic
anhydride to the reaction mixture will provide a mixture comprising both
polymerizable monomer and end-capping monomer, i.e., a halophthalimide having
only one reactive site which is thus capable of end-capping a growing polymer chain
in a polymerization reaction. In such a case, the use of phthalic anhydride to form
end-capping monomers may be used to control the molecular weight of the
polyetherimide produced in the subsequent polymerization reaction. In addition, as
known to those skilled in the art, other anhydrides may be utilized to form endcapping
monomers.
Any diamino compound may be employed in the method of this invention. Examples
of suitable compounds are ethylenediamine, propylenediamine, trimethylenediamine,
diethylenetriamine, triethylenetetramine, heptamethylenediamine,
octamethyienediamine, 1,12-dodecanediamine, 1,18-octadecanediamine, 3-
methylheptamethylenediamine. 4,4-dimethylheptamethylenediamine, 4-
methylnonamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,2-
dimethylpropylenediamine, N-methyl-bis(3-aminopropyl)amine, 3-
methoxyhexamethylcnediamine, 1,2-bis(3-aminopropoxy)ethane, bis(3-aminopropyl)
sulfide, 1,4-cyclohcxanediamine, bis-(4-aminocyclohexyl)methane, mphenylenediaminc,
p-phcnylenediamine, 2,4-diaminotpluene, 2,6-diaminotoiuene, mxylylenediaminc,
p-xylylenecliamine, 2-methyl-4,6-dicthyl-l,3-pheny!enediamine, 5-
mcthyl-4,6-diclhyl-l,3-phenylene-diamine. bencidirie, 3",3'-'dirriethylbenzidine. 3,3'-
dimethoxybenzidine, ].5-d^"imonaphthalene, bis(4-aminophenyl)methane, bis(2-
rnTOTcF^ainino ',-'-OiethylphenyI)methane, bis(4-aminophenyl)propane, 2,4-bis((3-
amino-t-butyl)toluene. bis(p-p-methyl-o-aminopentyl)benzene, 1,3-diamino-4-
isopropylbenzene, bis(4-aminophenyl) sulfone. bis(4-aminophenyl) ether and 1,3-
bis(3-aminopropyl)tetramethyldisiloxane. Mixtures of these compounds may also be
present. The preferred diamino compounds are aromatic diamines, especially m- and
p-phenylenediamine and mixtures thereof.
The production of the bis(halophthalimide) preferably occurs in the presence of a nonpolar
organic liquid, usually having a substantially lower polarity than that of the
dipolar aprotic solvents such as dimethylformamide, dimethylacetamide and Nmethylpyrrolidinone.
Said non-polar solvent preferably has a boiling point above
about 100° C. and most preferably above about 150° C., in order to facilitate the
reaction which requires temperatures above that temperature. Suitable liquids of this
type include o-dichlorobenzene, dichlorotoluene, 1,2,4-trichlorobenzene, diphenyl
sulfone and alkoxybenzenes such as anisole and veratrole, and more generically
liquids whose polarity is no higher than those of the aforementioned liquids. Liquids
of similar polarity but lower boiling points, such as chlorobenzene, may be employed
at super-atmospheric pressures. Anisole and o-dichlorobenzene are usually preferred.
The bis(ha!ophthalimide) preparation method of the invention typically employs
temperatures of at least 110° C., preferably in the range from 150° to about 275° C.,
preferably about 175-225° C. At temperatures below 110° C., reaction rates are for
the most part too slow for economical operation. It is within the scope of the
invention to employ super-atmospheric pressures, typically up to about 5 atm, to
facilitate the use of high temperatures without causing liquid to be lost by evaporation
through boiling.
A further feature, for the same reason, is a solids content in the reaction mixture of at
least about 5%, preferably at least about 12% and most preferably about 15-25%, by
weigh). By "soniis content" is meant the proportion of bishalophthalimide product as
a percentage of the eta weight nf the bishalonhlhslimide and solvent. It is further
within the scope of the invention to chanyv. content during the reaction, for
such reasons as to effectuate transfer of the reaction
another.
Other constituent proportions in the reaction mixture preferably include, a molar ratio
of'anhvdrkie to dia;r.:ne m the range of from about 1.98:1 to about 2.04:1, with a r a t i o
of about 2:1 being most preferred. While other ratios may be employed, a slight
excess of anhydride or diamine may be desirable. Catalyst, if used, is present in an
amount effective to accelerate the reaction, usually about 0.1-0.3% by weight based
on the weight of diamine. Suitable imidization catalysts include, but are not limited
to, sodium phenyl phosphinate, acetic acid, benzoic acid, phthalic acid, or substituted
derivatives thereof. In one embodiment, sodium phenyl phosphinate is utilized as the
imidization catalyst.
The reaction between at least one amine reactant and at least one anhydride reactant
by the methods of the present invention results in products generally comprising
phthalimidcs of formula (I). Bis(lia)ophthalimides) which may be produced include
1,3- and l,4-bis -(4-fluorophthalimido)Jbenzene and 1,3- and l,4-bis[N-(3-
fluorophthalimido)]-benzene; and 4,4'-bis[N-(4-fluorophthalimido)]phenyl ether and
4:4'-bis[N-(3-fluorophthalimido)]phenyl ether; and the corresponding chloro, bromo
and nitro compounds. Mixtures of such compounds may also be employed.
Especially preferred substituted aromatic compounds of formula 1 include at least one
of K3-bis[N-(4-chlorophthalimido)]benzene, l,4-bis[N-(4-
chlorophthalimido)]benzene, 1,3-bis[N-(3-chlorophthalimido)]benzene, 1,4-bis[N-(3-
chlorophthalimido)]benzene. l-[N-(4-chlorophthalimido)]-3-[N-(3-
chlorophthalimido)benzene, or 1 -[N-(4-chlorophthalimido)]-4-[N-(3-
chlorophthalimido)benzene. Where the starling phthalic anhydride is pure 3-CIPA, a
3-3'-ClPAMl as depicted in reaction scheme ( I I ) is produced and then subsequently
reacted with additional components to produce the desired polyetherimide. However,
as noted above, in other embodiments a mixture of 3-C1PA with other phthalic
anhydrides, including 4-C1PA, dichlorophthalic anhydride, and phthalic anhydride,
may be utilized to produce the desired halophthalimide which, in turn, is then utilized
to produce the desired polyetherimide.
At least one dihydroxy-substituted aromatic hydrocarbon is then reacted'with the
CIPAMI lo produce the desired polyetherimide. Suitable dihydroxy-substituted
aromatic hydrocarbons include those having the formula
HO--A2,-OH, (111)
wherein A^ is a divalent aromatic hydrocarbon radical. Suitable A^ radicals include
m-phenylene, p-phenylenc, 4.4'-biphenylene, 4,4'-bi(3,5-dimethyl)phenylene, 2,2-
bis(4-phenylene)propane and similar radicals such as those which correspond to the
dihydroxy-substituted aromatic hydrocarbons disclosed by name or formula (generic
or specific) in U.S. Patent No. 4,217,438.
The A- radical preferably has the formula
--A3 -Y--A4 --, (IV)
wherein each of A^ and A^ is a monocyclic divalent aromatic hydrocarbon radical
and Y is a bridging hydrocarbon radical in which one or two atoms separate A-1 from
A'. The free valence bonds in formula IV are usually in the meta or para positions of
A 3 and A^ in relation to Y. Compounds in which A has formula IV are bisphenols,
and for the sake of brevity the term "bisphenol" is sometimes used herein to designate
the dihydroxy-substitutcd aromatic hydrocarbons; it should be understood, however,
that non-bisphenol compounds of this type may also be employed as appropriate.
In formula IV, the values may be unsubstiluted phenylene or halo or
hydrocarbon-substituted derivatives thereof, illustrative substituenls (one or more)
being alkyl, alkenyl, bromo, chloro. Unsubstituted phenylene radicals are preferred.
Both are preferably p-phenylene, although both may be - or -phenylene
or one o- or m-phenylene and the other p-phenylene.
The bridging radical, Y, is one in which one or two atoms, preferably one, separate
A-3 from A Illustrative radicals of this type are methylene, cyclohexylmethylene, 2-
[2.2.1 ]-bicycloheplylmethylene, ethylene, isopropylidene, neopen'ylidene,
cyclohexylidene, cyclopcniadecylidcne, cvclododecylidene and adamantylidene; gemalkylene
(alkylidene) radicals are preferred. Also included, however, are unsaturated
radicals.
Some preferred examples of dihydric phenols which may be utilized include 6-
hydroxy-1 -(4'-hvdroxyphenyl)-l ,3,3-trimethylindane, 4,4'-(3,3,5-trimethylcyclo-
hexylidene)diphenol; I,l-bis(4-hydroxy-3-methylphenyl)cyclohexane; 2,2-bis(4-
hydroxyphenyl)propane (commonly known as bisphenol-A); 2,2-bis(4-hydroxy-3,5-
dimethylphenyOpropane; 2,2-bis(4-hydroxy-3-methylphenyl)propane; 2,2-
bis(4hydroxy-3-ethylphenyl)propane; 2,2-bis(4-hydroxy-3-isopropylphenyI)propane;
2,4'-dihyroxydiphenylmethane; bis(2-hydroxyphenyl)methane; bis(4-hydroxyphenyl)
methane; bis(4-hydroxy-5-nitrophenyl)melhane; bis(4-hydroxy-2,6-dimethyl-
3-methoxyphenyl)melhane; 1,1 -bis(4-hydroxyphenyl)ethane; 1,1 -bis(4-hydroxy-2-
ch)orophenyl)ethane; 2,2-bis(3-phenyl-4-hydroxyphenyl)-propane; bis(4-
hydroxyphenyl)cyclohexylmethane; 2,2-bis(4-hydroxyphenyl)-l-phenylpropane;
resorcinol; C]_3 alkyl-substituted resorcinols. For reasons of availability and
particular suitability for the purposes of this invention, in one embodiment the
preferred dihydric phenol is bisphenol A in which the radical of formula IV is the 2,2-
bis(4-phenylene)propane radical and in which Y is isopropylidene and A^ and A^ are
each p-phenylene.
Preferably, the reaction of salts of dillydroxyaromatic compounds are utilized in the
methods of the present disclosure. More preferably, alkali metal salts of dihydroxysubstituted
aromatic hydrocarbons are employed. These alkali metal salts are
typically sodium or potassium salts, with sodium salts frequently preferred by reason
of their availability and relatively low cost. Most preferably, bisphenol A disodium
salt (BPA.NA2) is utilized.
In a preferred embodiment, bisphenol A disodium salt is added to the organic solvent
and the mixture azeotroped to a dry condition. Then, a second co-monomer, for
example a bis[N-(ch!orophthalimido)]benzene, may be added and the mixture
azeotroped to a dry condition. Then a catalyst may be added as a pre-dried solution in
organic solvent. The process is expedited when predried solvent and co-monomers
are used.
One class of preferred solvents utilized in producing the polyetherimide includes
those of low polarity. Suitable solvents of this type include halogenated aromatic
compounds such as o-dichlorobenzene, dichlorotoluene and 1,2,4-trichlorobenzene;
and diphenyl sulfone. Solvents of similar polanty but lower boiling points, such as
chlorobenzene, may be employed at superatmospheric pressures. Another class of
preferred solvents includes aromatic ethers such as diphenyl ether, phenetole
(ethoxybenzene), and anisole (melhoxybenzene). O-dichlorobenzene and
alkoxybenzenes, most preferably anisole, are particularly preferred. In many
instances, halogenated aromatic solvents are preferred over alkoxybenzenes since the
former have less tendency than the latter to interact with and inactivate the phase
transfer catalyst described below. Another class of solvents suitable for the present
invention is polar aprotic solvents, illustrative examples of which include
dimethylfonnamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide
(DMSO), and N-methylpyrrolidinone (NMP).
The preferred phase transfer catalysts, by reason of their exceptional stability at high
temperatures and their effectiveness to produce high molecular weight aromatic
polyether polymers in high yield are the hexaalkylguanidinium and a.oibis(
pcnlaalkylgiKim'diimirn)alkane salts. For the sake of brevity, both types of sails
are hereinafter sometimes designated "guanidinium salt".
Suitable guanidinium salts are illustrated by those of the formula
wherein:
is a primary alkyl radical and is a primary alkyl or
bis(primary alkylene) radical, or at least one of the R2 -R3, R4 -R5 and R°—R7
combinations with the connecting nitrogen atom forms a heterocyclic radical;
X^ is an anion; and
n is 1 or 2.
The alkyl radicals suitable as R6 include primary alkyl radicals, generally
containing about 1-12 carbon atoms. R' is usually an alkyl radical of the same
structure as R^-6 or a C2 alkylene radical in which the terminal carbons are
primary; most preferably, it is C2-6 alkyl or straight chain alkylene.
Alternatively, any combination of and the corresponding nitrogen atom(s) may
form a heterocyclic radical such as piperidino, pyrroio or morpholino.
The value may be any anion and is preferably an anion of a strong acid; examples
are chloride, bromide and methanesulibnate. Chloride and bromide ions are usually
preferred. The value of n will be 1 or 2 depending on whether R ' is alkyl or alkylene.
As can be seen in formula V. the positive charge in the guanidinium salt is delocalized
over one carbon and three nitrogen atoms. This is believed to contribute to the salts'
stability under the relatively high temperature conditions encountered in embodiments
of the invention.
Additionally, the reaction is typically sensitive to water and it is preferable to dry the
solvent-comprising reaction mixture by known methods, for example by boiling or
azeotroping water from the mixture, typically prior to delivering the catalyst. In one
embodiment, water removal from the system can be accomplished in either batch,
semi-continuous or continuous processes using means well-known in the art such as a
distillation column in conjunction with one or more reactors. In one embodiment, a
mixture of water and non-polar organic liquid distilling from a reactor is sent to a
d i s t i l l a t i on column where water is taken off overhead and solvent is recycled back
into the reactor at a rate lo maintain or increase desired solids concentration.
Other methods for water removal include, but are not limited to, passing the
condensed distillate through a drying bed for chemical or physical adsorption of
water.
Once the formation of the desired resin has occurred, the polymer solution, e.g.,
polyetheri'mide in o-DCB, is placed in contact with an anti-solvent which is capable of
dissolving low molecular weight species such as unreacted monomers, and
undesirable products such as cyclic oligomers and/or linear oligomers. The antisolvent
does not, however, dissolve the polymer, e.g., the polyetherimide. Suitable
anti-solvents for use in accordance with the present disclosure include toluene,
ketones, preferably acetone, tetrahydrofuran, xylenes, dioxane, etc.
In those cases where the polymer is not already in solution, a suitable solvent may be
added to the polymer to produce a polymer solution for fractionation. Such solvents
include, but are not l i m i t e d to. o-DCB, trichlorobenzene, anisole, and veratrolc. Once
the polymer solution has been formed, the anti-solvent is added as described above.
In one embodiment, polyetherimide solution is heated to a temperature ranging
from about 50° C. to about 180° C., preferably from about 80° C. to about 1 10r C.,
with a temperature of from about 90° C. to about 100° C. being most preferred.
While stirring, an anti-solvent such as toluene is added. It is desirable to add the
maximum amount of anti-solvent without precipitation of the solid polymer.
Preferably, the anti-solvent is added in an amount ranging from about 1/10 to about
1/2 by weight of the solvent in the polymer solution, more preferably in an amount
equal to about 1/3 by weight of the solvent in the polymer solution.
Once the anti-solvent has been added, (he solution is preferably heated to a
temperature ranging from about 100° C. to about 180° C., preferably from about 135°
C. to about 150° C.. with a range of from about 140° C. to about 145° C. being most
preferred. Stirring is stopped and the polymer solution is allowed to cool. Phase
separation starts to occur and is complete in about 1 to about 2 hours.
The phases may then he separated by methods known to (hose skilled in the art
including, but not limited to. settling. For polyelherimides. two phases are obtained
after separation: the light phase of o-DCB and toluene is rich in cyclic and linear
oligomers; the heavy phase contains about 20-25% solids, including the desired
polymer.
The level of reduction in the polydispersivily of the resulting polymers is directly
related to the amount of anti-solvent used. In this manner, the polydispersivity of the
polymer may be reduced. For example, in the case of polyetherimides, the resulting
polyelherirnide preferably has a reduced polydispersivity. In one embodiment, the
polydispersivity ranges from about 1.5 to about 2.5, more preferably from about 2.0 to
about 2.3.
Polyetherimide resins produced in accordance with the methods of the present
disclosure have improved thermomechanical performance characteristics such as glass
transition temperature (Tg) or heat deflection temperature (HDT).
In.one embodiment, the method of the present disclosure includes concentrating and
recovering the cyclic and low molecular weight linear oligomers from the light phase
for use in other applicalions such as re-equilibration to high molecular weight
polymer or in processes where improved flow is needed.
The present disclosure is illustrated by (he following non-limiting examples.
EXAMPLE 1
Four samples of a polyetherimide solution produced by reacting bisphenol-A salt with
a CIPAMi produced by reacting tnPD and 3-C1PA were prepared. 70:30
compositions were prepared by dissolving the polyetherimide in o-DCB and heating it
to 180° C. with stirring to obtain a solution having a concentration of 10% solids. 5
grams of a 10% polymer solution (0.5 g polymer in 4.5 g o-DCB) were prepared with
varying amounts (0.3, 0.5, 1.0 and 1.5 g) of toluene as an anti-solvent. The samples
and the amounts of toluene used arc set forth below in Table I .
The polyetherimide solution was heated to a temperature ranging from 90° C. to 100°
C. While stirring, toluene was added to each sample in the amounts noted above.
The solution was then heated to a temperature from 140° C. to 145° C. to clear any
turbidity. Stirring was stopped and (he polymer solution was allowed to cool. Phase
separation started to occur and was complete in about 1 to about 2 hours. In each case
the solution fractionated into two phases - one light and one heavy.
The light and heavy phases obtained from each sample were then subjected to gel
permeation chromatography (GPC) analysis. GPC analysis for high polymer was
performed by using chloroform as eluent (elution rate of 0.8 ml*min-1) on a HP 1100
Series apparatus equipped with a PL gel 5 urn Mixed-C column and a UV detector
utilizing the manufacturer's software. The % cyclics analyses were determined on a
Polymer Labs HT-120 GPC system equipped with a PL gel Mixed-C column and UV
detector, using chloroform as an eluent at 0.7 mL/min and utilizing Perkin Elmer
Turbochrom software. Table 2 summarizes the GPC results.
As can be seen from Table 2, the polydispersivity narrowed as the amount of toluene
increased. There was a slight increase in the weight average molecular weight of the
polymer as the polydispersivity was reduced. Moreover, as the amount of toluene
increased, the Mw of the extracted polymer in the light phase was reduced. The total
amount of cyclics in the heavy phase was reduced as additional cyclics were found in
the light phase. As is apparent from Table 2, the volume of the light phase increased
with the amount of toluene used. Therefore, heavy phase from sample 4 had the most
concentrated polymer sample.
EXAMPLE 2
Three different polyelherimide resins were produced by reacting a bisphenol-A salt
with a C1PAM1 monomer prepared from 70:30 4/3-CIPA and mPD (designated as
samples 5, 6 and 7 in Table 3). Another sample was prepared by reacting a bisphenol-
A salt with a C1PAMI monomer produced from 3-C1PA and mPD (designated as
sample 8 in Table 4). Samples were fractionated by the addition of toluene and
polydispersivity determined following the methods of Example 1.
Table 3 demonstrates the results of the fractionation and the ability of the present
methods to lower the polydispersivity of the samples. As is apparent from Table 4,
the 3-C1PA based polyetherimide possessed a large amount of cyclics, which were
successfully separated by the methods of the present invention.
As is also apparent from the above, the level of reduction in the polydispersivity of
the resulting polymers was directly related to the amount of toluene used.
While the disclosure has been illustrated and described in typical embodiments, it is
not intended to be limited to the details shown, since various modifications and
substitutions can be made without departing in any way from the spirit of the present
disclosure. For example, while much of the specification describes the fractionation
of a polymer solution containing a polyetherimide and its undesirable side products
and unreacted monomers, the methods of the present disclosure can be utilized to
fractionate any polymer solution and thereby lower the polydispersivity of the desired
polymer. As such, further modifications and equivalents of the disclosure herein
disclosed may occur to persons skilled in the art using no more than routine
experimentation, and all such modifications and equivalents are believed to be within
the spirit and scope of the disclosure as defined by the following claims.

CLAIMS:
1. A method for reducing the polydispersivity of a high molecular weight
polymer comprising:
forming a polymer solution;
contacting the polymer solution with an anti-solvent capable of dissolving low molecular weight species but not the high molecular weight polymer;
allowing phase separation to occur to obtain a light phase and a heavy phase, and
recovering the desired polymer from the heavy phase,
wherein the resulting polymer possesses a reduced polydispersivity.
2. The method of claim 1 wherein the step of contacting the polymer solution
with the anti-solvent comprises an anti-solvent selected from the group consisting of
toluene, ketones, acetone, tetrahydrofuran, xylenes, and dioxane.
3. A method for reducing the polydispersivity of a high molecular weight
polyetherimide resin comprising:
forming a polyetherimide solution;
contacting the polyetherimide solution with an anti-solvent capable of dissolving low molecular weight species but not the high molecular weight polyetherimide;
allowing phase separation to occur to obtain a light phase and a heavy phase; and recovering the desired polyetherimide from the heavy phase,
wherein the resulting polyetherimide possessed a polydispersivity ranging from about 1.5 to about 2.5.

4. The method of claim 3 wherein the step of forming a polyetherimide resin
further comprises forming a polyetherimide by reacting a bis-halophthalimide with at
least one alkali metal salt of a dihydroxy-substituted aromatic compound in the
presence of a phase transfer catalyst.
5. The method of claim 4 wherein the step of forming the polyetherimide resin
further comprises forming a polyetherimide by reacting a halophthalimide with
bisphenol A disodium salt.
6. The method of claim 3 wherein the step of forming the polyetherimide
solution comprises using a solvent selected from the group consisting of o-
dichlorobenzene and anisole.
7. The method of claim 3 wherein the step of contacting the polyetherimide
solution with the anti-solvent comprises an anti-solvent selected from the group
consisting of toluene, kctones, acetone, tetrabydrofuran, xylenes, and dioxane.
8. A polyetherimide resin produced in accordance with the method of claim 3.
9. A method for reducing the polydispersivity of a high molecular weight
polyetherimide resin comprising:
forming a polyetherimide solution by reacting a halophthalimide produced by reacting a diamino compound selected from the group consisting of m-phcnylenediamine and p-phenylenediamine with an anhydride selected from the group consisting of 3-chlorophthalic anhydride, 4-chlorophthalic anhydride, dichloro phthalic anhydride, phthalic anhydnjc and mixtures thereof, and then reacting the halophthalimide with bisphenol A disc-dium salt in the presence of a phase transfer catalyst selected from the group consisting of hexaalkylguanidinium alkane salts or a a,co-bis(pentaalkylguanidinium)alkane salts;
contacting the polyetherimide solution with an anti-solvent capable of dissolving low molecular weigh', species but not the high molecular weight polyetherimide selected from the group consisting of toluene, ketones, acetone, tetrahydrofuran, xylenes, and dioxane;

allowing phase separation to occur to obtain a light phase and a heavy phase; and recovering the desired polyethenmide from the heavy phase,
wherein the resulting polyetherimide possessed a polydispersivity ranging from about 1.5 to about 2.5.
10. A polyelherimide resin produced in accordance with the method of claim 9.