Abstract: A method of producing a polyether copolymer by reacting a dihalogenobenzonitrile, 1,4-bis(4'-halobenzoyl)benzene, with 4,4'-biphenol in an aprotic polar solvent in the presence of an alkali metal compound to produce a polyether copolymer having repeating units represented by the following general formula (I) ##STR1## and the repeating units represented by the following formula (II) ##STR2## The molar ratio of the repeating units represented by the formula (I) based on the total of the repeating units represented by the formula (I) and the repeating units represented by the formula (II) (the molar ratio of (I)/{(I)+(II)}) is from 0.1 to 0.8. The polyether copolymer has a melt viscosity (the viscosity under no shearing stress) of at least 500 poise as measured 400.degree. C.

Abstract: Polymers and copolymers having high glass transition temperature and which are soluble in organic solvents are produced from highly hindered biphenols, in particular polyetherketones, polyethersulfones, polyesters and polyetherimides, as well as copolymers based on these polymers may be produced for a variety of applications.

Abstract: Polyimide compositions, films, and electronic devices using polyimides, based on 9-aryl-9(perfluoroalkyl)-xanthene-2,3,6,7-dianhydride and one or more diamines from a selected group, which offers to the polyimides a combination of desirable properties including solubility, pseudo rod-like structure, low linear coefficient of thermal expansion, high glass transition temperature, low dielectric constant, and high modulus.

Abstract: An aromatic polyestersulfone having improved heat resistance, film-forming property, hydrolysis resistance and mechanical strength which comprises 1 to 100% by mole of recurring units of the general formula: ##STR1## and 99 to 0% by mole of recurring units of the general formula: ##STR2## wherein R and R' are the same or different and each is an alkyl or alkoxyl group having 1 to 4 carbon atoms, Ar is a bivalent aromatic group, and x and y are 0 or an integer of 1 to 4 provided that the sum of x and y is from 1 to 8.

Abstract: The present invention relates to a novel class of aromatic diamine monomers, benzoxazole polymers made from said class of monomers, and polymer-matrix composites which may be produced therefrom. The present invention also relates to methods of producing said polymers and said polymer-matrix composites. The polymer-matrix composites have as one advantage high strength and temperature resistance.

Abstract: A copolyesterimide composed of bis-trimellitimide units, 2,6-naphthalenedicarboxylic acid units, hydroquinone units and p-hydroxybenzic acid units. This copolyesterimide is melt-processable, and excels in heat resistance and mechanical properties.

Abstract: A method for the preparation of a variety of engineering polymers and copolymers, in particular aromatic polymers and copolymers which comprises reacting a stannylated reactant containing a first monomeric or polymeric moiety with an electrophilic reactant, usually a di(acid chloride) containing a second monomeric or polymeric moiety. The intermediate and second compound react by way of a condensation reaction to eliminate the tin and polymerise together the first and second moieties. Some novel polymers and copolymers can be prepared using this method.

Abstract: The invention relates to novel aryl carbonate cyanoaryl ether copolymers.

Abstract: Disclosed are rigid fluorinated monomers, their preparation, and polymers derived therefrom based on two novel tricyclic xanthene core systems, 9,9-bis(perfluoroalkyl)xanthene (I) and 9-phenyl-9-perfluoroalkylxanthene (II). The monomers have utility in the preparation of advanced high-performance polymers, particularly polyimides.

Abstract: Flame-resistant thermoplastic branched polycarbonates of high molecular weight are prepared from:(1) a carbonate precursor;(2) at least one dihydroxyaromatic compound of formula: ##STR1## where: R is a single bond, or a substituted or non-substituted linear or branched C.sub.1 -C.sub.5 alkylene radical, or a group chosen from O, S, SO.sub.2 and CO;X and Y, which may be the same or different, are H or CH.sub.3 ;m and n, which may be the same or different, are whole numbers from 1 to 4;(3) at last one halogenated pyrimidine compound of formula: ##STR2## where: R.sub.2, R.sub.3, R.sub.4, which may be the same or different, are chlorine or bromine or hydrogen, on condition that at least one is chlorine or bromine;R.sub.1 is chlorine or bromine, or a radical of formula: ##STR3## where Z is NH or S or O; (4) at least one polyfunctional organic compound as branching agent, characterized by possessing at least three equal or different groups chosen from the groups OH, COOH, COCl and SO.sub.2 Cl.

Abstract: Disclosed are rigid fluorinated monomers, their preparation, and polymers derived therefrom based on two novel tricyclic xanthene core systems, 9,9-bis-(perfluoroalkyl)xanthene (I) and 9-phenyl-9-perfluoroalkylxanthene (II). The monomers have utility in the preparation of advanced high-performance polymers, particularly polyimides.

Abstract: Aromatic polyesters based on isophthalic acid, terephthalic acid, p-hydroxybenzoic acid, hydroquinone and an arylene diol are described. The five monomers ae used in well-specified proportions and yield polymers that display an excellent overall combination of mechanical and thermal properties. The subject copolyesters have melting points of at least about 260.degree. C.; their heat distortion temperatures are at least about 200.degree. C. they have fiber ratings of up to 3. The novel polymers can be melt-fabricated using standard injection molding, extrusion and melt-spinning techniques.

Abstract: The present invention relates to aromatic compounds corresponding to formula (I) ##STR1## to their production and to their use as modifiers for thermoplastic aromatic polycarbonates and/or thermoplastic aromatic polyester carbonates and/or thermoplastic aromatic polyesters.

Abstract: The present invention relates to aromatic compounds corresponding to formula (I) ##STR1## to their production and to their use as modifiers for thermoplastic aromatic polycarbonates and/or thermoplastic aromatic polyester carbonates and/or thermoplastic aromatic polyesters.

Abstract: Disclosed are rigid fluorinated monomers, their preparation, and polymers derived therefrom based on two novel tricyclic xanthene core systems, 9,9-bis(perfluoroalkyl)xanthene (I) and 9-phenyl-9-perfluoroalkylxanthene (II). The monomers have utility in the preparation of advanced high-performance polymers, particularly polyimides.

Abstract: Flame-resistant thermoplastic branched polycarbonates of high molecular weight are prepared from:(1) a carbonate precursor;(2) at least one dihydroxyaromatic compound of formula: ##STR1## where: R is a single bond, or a substituted or non-substituted linear or branched C.sub.1 -C.sub.5 alkylene radical, or a group chosen from O, S, SO.sub.2 and CO;X and Y, which may be the same or different, are H or CH.sub.3 ;m and n, which may be the same or different, are whole numbers from 1 to 4;(3) at least one halogenated triphenolbenzamido compound of formula: ##STR2## where: Z is a group chosen from CO and SO.sub.2 ;R.sub.1 is chlorine or brominep is 1 or 2.

Abstract: Thermoplastic branched polycarbonates of high molecular weight and which possess flame-resistant (self-extinguishing) properties are provided wherein said polycarbonates contain in addition to carbonate units, units derived from a dihydroxyaromatic compound, units derived from a halogenated triphenyl compound and units derived from a polyfunctional organic branching agent.

Abstract: This invention relates to copolyestercarbonate polymers which are prepared with diaryl dicarboxylic acid compounds, particularly biphenyldicarboxylic acid compounds. Such copolyestercarbonate polymers show good physical properties including high glass transition temperatures and low ultraviolet radiation sensitivity. The thermoplastic copolymestercarbonates can be used to prepare films or molded articles or blended with other thermoplastic resins to give thermoplastic polymer blends for molding purposes.

Abstract: An organic polyarylate containing a repeating unit represented by the formula; ##STR1## wherein X is at least one member selected from the group consisting of --O--, --S--, --SO.sub.2 --, --CO--, alkylene, alkenylene and following formulas; ##STR2## and R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, and R.sub.7 respectively show a hydrogen atom, a halogen atom or a C.sub.1 -C.sub.10 alkyl group; said polyarylates having an inherent viscosity of at least 0.2 dl/g measured at 25.degree. C. in a solution of 1 g of the polarylate in 100 ml of a mixture of 50% by weight of phenol and 50% by weight of 1,1,2,2-tetrachloroethane.

Abstract: A thermoplastically processible aromatic polyetheramide, in which the structure comprises the repeating units of the formulae--CO--AR--CO-- (A)and--NH--Ar--O--Ar--X--Ar--O--Ar--NH-- (B)in which Ar signifies a bivalent unsubstituted or substituted aromatic radical having 6 carbon atoms, and whose linkages are in the p-position and X denotes a 2,2-propylidene linkage, the polyetheramide having an intrinsic viscosity [.eta.] in the range of 50 to 750 cm.sup.3 /g, and a glass transition temperature of above 200.degree. C., and a process for its production. The production of the polyetheramide is carried out by a low temperature solution condensation process, a solid phase condensation process, an interfacial condensation process or a melt condensation process.

Abstract: Thermotropic liquid crystalline polymers represented by the formulas as illustrated in FIGS. 1 and 2 wherein m, n, and o represent the number of monomer segments present; and x, y, and z are independently selected from the group consisting of alkyl, substituted alkyl, alkylene, and substituted alkylene.

Abstract: This invention relates to moldable polyarylates and in particular to moldable polyarylate compositions which have repeating units derived from bis-(3,5-dimethyl-4-hydroxyphenyl) sulfone (TMBS), optionally a dihydric phenol such as 2,2-bis-(4-hydroxyphenyl)-propane (Bisphenol A) and a mixture of isophthalic acid and terephthalic acid or derivatives thereof. Such polyarylates exhibit improved hydrolytic stability.

Abstract: The liquid crystal polycondensates according to the invention based on aromatic hydroxycarboxylic acids, if appropriate aromatic aminocarboxylic acids, diphenols, if appropriate aminophenols, aromatic dicarboxylic acids and if appropriate carbonic acid which are obtainable by polycondensation of the difunctional monomers mentioned in the melt in the presence of aromatic esters with a defined sequence of the structural units of the formula ##STR1## of oligomers with random distribution of the structural units of the formula ##STR2## have a good heat stability and exhibit a stable viscosity under the processing conditions. The liquid crystal polycondensates can be used for the production of shaped articles, films, fibers and filaments.

Abstract: Disclosed herein are a coppolymerized polyester produced by copolymerizing a dicarboxylic acid component (A) comprising(a) 10 to 90 mol % of isophthalic acid or an ester forming derivative thereof,(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by the formula [I]: ##STR1## (wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 each represent a hydrogen atom, an alkyl group having 1 to 6 carbon atom, an alkoxy group having 1 to 6 carbon atom, a phenyl group, a chlorine atom, a bromine atom or a fluorine atom), or as ester forming derivative thereof, and(c) 0 to 45 mol % of a naphthalenedicarboxylic acid or an ester forming derivative thereof, anda diol component (B); and a polyester composition containing the copolymerized polyester.

Abstract: Fire-retardant polycarbonates, polyester carbonates and polyesters based on dihydroxydiphenyl cycloalkanes ##STR1## in which R.sup.1 and R.sup.2 independently of one another represent hydrogen, halogen, preferably chlorine or bromine, C.sub.1 -C.sub.8 alkyl, C.sub.5 -C.sub.6 cycloalkyl, C.sub.6 -C.sub.10 aryl, preferably phenyl and C.sub.7 -C.sub.12 aralkyl, preferably phenyl-C.sub.1 -C.sub.4 -alkyl, more especially benzyl,m is an integer of 4 to 7, preferably 4 or 5, R.sup.3 and R.sup.4 may be individually selected for each X and, independently of one another, represent hydrogen or C.sub.1 -C.sub.6 alkyl andX is carbon,with the proviso that, at at least one atom X, R.sup.3 and R.sup.4 are both alkyl,the fire-retardant finish being provided by additives and/or comonomers.

Abstract: Copolyimides derived from the reaction product of 3,3'-6 F diamine or 4,4'-6 F diamine, at least one other diamine, and pyromellitic dianhydride can be rendered solvent soluble while at the same time exhibiting an improvement in both mechanical and electrical properties by the inclusion of at least one other dianhydride having a diaryl nucleus in the reaction media. Suitable such dianhydrides include bis (3,4 dicarboxy phenyl) ether dianhydride, 3,3'4,4' benzophenone tetracarboxylic dianhydride, 3,3',4,4' diphenyl tetracarboxylic acid dianhydride and 2,2 bis(3,4 dicarboxyphenyl) hexafluoropropane dianhydride (6F-DA). Such polyimides are soluble in common organic solvents such as methyl ethyl ketone or N-methyl pyrrolidone, and exhibit excellent film forming properties with improved mechanical and electrical properties as compared to the corresponding homopolyimides. They possess excellent heat stability (Tg's in excess of about 350.degree. C.

Abstract: A polycarbonate resin comprising either a structural unit derived from a spiro ring-containing dihydric phenol, or such a structural unit and a structural unit derived from a dihydric phenol, and a process for producing the same. The polycarbonate resin has excellent flowability and moldability, and also improved optical properties (low refractive index, large Abbe number, etc.), and can be advantageously used in various fields, e.g., as a material for molded articles for optical use and other precision molded articles.

Abstract: Thermotropic liquid-crystalline aromatic polyesters processable in the molten state, comprising units derived from at least one dicarboxy aromatic acid having the formula:HOOC--Ar.sub.1 --O--Ar.sub.2 --COOH (1)wherein Ar.sub.1 and Ar.sub.2 are aromatic radicals from aromatic diols, and, possibly, from other diacids and/or hydroxy acids.

Abstract: Liquid-crystalline, thermotropic, aromatic polyesters processable in the molten state, comprising units derived from hydroquinone mono- and possibly di-substituted with aralkyl groups.

Abstract: A photoconductive imaging member comprised of a photogenerating layer, and a charge transport layer comprised of the N,N-bis(biarylyl)aniline charge transport polymers of the formula ##STR1## wherein A and B are independently selected from bifunctional linkages; Z is alkylenedioxy, arylenedioxy, or substituted derivatives thereof; R and R' are alkyl, aryl, alkoxy, aryloxy, or halogen; x and y are mole fractions wherein x is greater than 0 and the sum of x and y is equal to 1.0; a and b are the numbers 0, 1 or 2; and n represents the number of monomer units.

Abstract: The present invention is a class of polymeric membranes formed from aromatic polyarylates derived from dicarboxylic acid chlorides and cardo bisphenols having halo substituents on all portions ortho to the hydroxy functions. These polyarylate membranes exhibit high gas permselectivities and are useful in various gas separation applications.

Abstract: An aromatic polyester carbonate comprising structural units represented by the following formulae (A), (B), (C), and (D) and satisfying the following relationship when the mole fractions of the structural units represented by the formulae (A), (B), (C), and (D) are defined as a, b, c, and d, respectively: ##EQU1## and having an inherent viscosity [.eta..sub.inh ] in a solution at a concentration of 0.5 g/dl in p-chlorophenol as a solvent at 50.degree. C. of 1.0 dl/g or higher, or being insoluble in the solvent, and having liquid crystal properties ##STR1## wherein R is the same or different and represent an alkyl, phenyl group or a halogen, and n represents an integer of 0 to 4; ##STR2## X.sup.1 represents a substituted or non-substituted phenyl group, an alkyl group having 3 to 6 carbon atoms or a halogen;X.sup.2 represents --O--, --S--, ##STR3## or --CH.sub.2 --; X.sup.3 may be the same or different and represents an alkyl group, phenyl group, or a halogen; and m represents an integer of 0 to 4.

Abstract: A polyarylate is formed by reacting a mixture of a diester of a dihydric phenol, at least one aromatic dicarboxylic acid and an inert diluent comprising a poly(fluorinated alkylene oxide). Polyarylates of improvided color can be formed and the diluent can be easily separated from the polyarylate and reaction byproducts.

Abstract: Provided is a wholly aromatic polyester superior in melt processability and tenacity which consists essentially of the following structural units (A), (B) and (C) and wherein 0.2 to 40 mole % of the total of said units are of ortho configuration; ##STR1## where Ar.sup.1 and Ar.sup.2 each represent a divalent aromatic hydrocarbon group having 6 to 20 carbon atoms, the hydrogen atoms of said aromatic hydrocarbon group may be substituted with a halogen atom, an alkyl or alkoxy group having 1 to 4 carbon atoms, or phenyl; Z is ##STR2## --O--, or --SO.sub.2 --; m is 0 or 1, at least 60 mole % of Ar.sup.1 being constituted by a group selected from 1,4-phenylene, substituted 1,4-phenylenes, naphthyl and 4,4'-biphenyl.

Abstract: Smooth, thin, dimensionally stable, essentially circular and planar injection-molded disc members, well adapted as substrates for magnetic recording discs, e.g., by providing same with an effective recording amount of a magnetic coating material on at least one of the face surfaces thereof, comprise a radially molecularly oriented thermotropic polymer, desirably having a flow temperature ranging from 200.degree. C. to 350.degree. C. and an inherent viscosity of at least 1 dl g.sup.-1.

Abstract: The new thermotropic polyesters containing recurring structural units corresponding to the following formulae ##STR1## show excellent mechanical properties and good processibility. They may be used in the usual way for the production of moldings, filaments, fibers and films.

Abstract: A film made from aromatic copolyamides of the dicarboxylic acid diamine type, whose shaping substance comprises certain recurring structural units and which has specific criteria regarding Staudinger index, tear strength, volume resistance, electrical dielectric strength, dimensional stability and water absorption, a process for its production, and the use of the film for the production of heat-resistant insulation material or as a substrate for flexible circuit boards.

Abstract: The present invention provides polyamide-polyimide and polybenzoxazole-polyimide polymers derived therefrom with improved processing and film characteristics having incorporated into the polymeric backbone the polymeric condensation residuum of novel aromatic diamino compounds having the formula: ##STR1## wherein A is selected from the group consisting of SO.sub.2, O, S, CO, C.sub.1 to C.sub.6 alkyl, perfluoroalkyl or perfluoroarylalkyl having from 1 to 10 carbon atoms and a carbon-carbon double bond directly linking the two aromatic groups, and R is selected from the group consisting of hydrogen, hydroxy and C.sub.1 to C.sub.4 alkoxy.The polyamide-polyimide polymers of this invention are prepared by reacting compounds of the above formula, alone or admixed with other aromatic diamines, with one or more aromatic tetarcarboxylic acids or anhydrides thereof. Polybenzoxazole-polyimide derivatives of such polyamide-polyimide polymers are prepared utilizing compounds of the above formula wherein R is hydroxy or C.

Abstract: The present invention provides polyamide-polyamide-polyimide and polybenzoxazole-polyamide-polyimide polymers derived therefrom with improved processing and film characteristics having incorporated into the polymeric backbone the polymeric condensation residuum of novel aromatic diamino compounds having the formula: ##STR1## wherein A is selected from the group consisting of SO.sub.2, O, S, CO, C.sub.1 to C.sub.6 alkylene, perfluoroalkylene or perfluoroarylalkylene having from 1 to 10 carbon atoms and a bond directly linking the two aromatic groups, and R is selected from the group consisting of hydrogen, hydroxy and C.sub.1 to C.sub.4 alkoxy.The PA-PA-PI polymers of this invention are prepared by reacting compounds of the above formula alone or admixed with other aromatic diamines, with carboxyphenyl trimellitimide or the acid halide or ester derivatives thereof, alone or admixed with one or more aromatic diacid chlorides and/or one or more aromatic tetracarboxylic acids or anhydrides thereof.

Abstract: The present invention provides polyamide-polyamide and polybenzoxazole-polyamide polymers derived therefrom with improved processing and film characteristics having incorporated into the polymeric backbone the polymeric condensation residuum of novel aromatic diamino compounds having the formula: ##STR1## wherein A is selected from the group consisting of SO.sub.2, O, S, CO, C.sub.1 to C.sub.6 alkylene, perfluoroalkylene or perfluoroalkylene having from 1 to 10 carbon atoms and a bond directly linking the two aromatic groups and R is selected from the group consisting of hydrogen, hydroxy and C.sub.1 to C.sub.4 alkoxy.The polyamide-polyamide polymers of this invention are prepared by reacting compounds of the above formula, alone or admixed with othr aromatic diamines, with one or more aromatic or aliphatic dicarboxylic acid or amide-forming derivatives thereof.

Abstract: Novel aromatic polyamides high in heat resistance and soluble in various organic solvents are obtained each by reacting 2,2'-bis[4-(4-aminophenoxy)phenyl]-hexafluoropropane or a simple derivative thereof with an aromatic dicarboxylic acid, e.g. isophthalic acid, or its dihalide or diester.

Abstract: A thermotropic copolyester, showing a liquid-crystalline structure of nematic type within a desired temperature range, contains units deriving from:(a) a saturated bicarboxy aliphatic acid;(b) 4,4'-di-hydroxydipheryl;(c) 4-hydroxybenzoic acid; and(d) 4-hydroxy-benzoic acid bearing an alkyl substituent or a halogen atom bonded to the aromatic ring.Such a copolyester constitutes a material endowed with self-reinforcing characteristics, originating, through the usual transformation processes by injection or by extrusion techniques, marked molecular orientations, which supply the manufactured articles with high stiffness characteristics.Said material can be also used as a reinforcing agent when is mixed, by means of the usual techniques, with the traditional thermoplastic polymers.

Abstract: Liquid-crystalline, thermotropic, aromatic polyesters processable in the molten state, comprising units derived from hydroquinones substituted with aryl, aralkyl and aroyl groups, and from phenoxy-hydroquinone.

Abstract: Described herein are novel crystalline polyarylnitrile polymers which have excellent mechanical and thermal properties. Also, described is a process for producing such polyarylnitrile polymers.

Abstract: A method for the preparation of a variety of engineering polymers and copolymers, in particular aromatic polymers and copolymers which comprises reacting a stannylated reactant containing a first monomeric or polymeric moiety with an electrophilic reactant, usually a di(acid chloride) containing a second monomeric or polymeric moiety. The intermediate and second compound react by way of a condensation reaction to eliminate the tin and polymerise together the first and second moieties. Some novel polymers and copolymers can be prepared using this method.

Abstract: Disclosed herein are a copolymerized polyester produced by copolymerizing a dicarboxylic acid component (A) comprising(a) 10 to 90 mol % of isophthalic acid or an ester forming derivative thereof,(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by the formula [I]: ##STR1## (wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 each represent a hydrogen atom, an alkyl group having 1 to 6 carbon atom, an alkoxy group having 1 to 6 carbon atom, a phenyl group, a chlorine atom, a bromine atom or a fluorine atom), or an ester forming derivative thereof, and(c) 0 to 45 mol % of a naphthalenedicarboxylic acid or an ester forming derivative thereof, anda diol component (B); and a polyester composition containing the copolymerized polyester.

Abstract: Liquid crystalline side-chain polyesters prepared by polycondensing a dicarboxylic acid or a derivative thereof with a diol of a certain general formula. Of such diols the essence is that they have a delocalized .pi. electron system to which both an electron donor group and an electron acceptor group are coupled directly (D.pi.A-system). Because of the structure of the diol to which the D.pi.A-system is linked the polyesters exhibit excellent Tg and Tc values. The polyesters are to be used in optical waveguides or for optical data storage.

Abstract: A class of amide group-containing aromatic dihalide compounds are sulfidized together with a class of aromatic dihalide compounds to provide a novel class of aromatic sulfideamide polymers increased in crystalline melting point (T.sub.m). The polymers exhibit excellent resistance to high temperatures, resistance to solvents, flame-retardant properties and improved mechanical properties.

Abstract: High molecular weight thermotropic aromatic copolyesteramides which can be molded/extruded into a wide variety of useful shaped articles having improved thermomechanical properties are comprised of recurring structural units of the formulae (I), (III) and (IV), and optionally (II), wherein:(I) represents the structure: ##STR1## in which R.sub.1 is a methyl or ethyl radical or a chlorine or bromine atom, with the proviso that the units (I) may be identical or different,(II) represents the structure: ##STR2## (III) represents the structure: ##STR3## in which n is an integer from 2 to 6, with the proviso that the units (III) may be identical or different,(IV) represents the structure: ##STR4## the molar ratio of the units (I) relative to the sum of the units (II)+(III) ranges from 0.95 to 1.

Abstract: The present invention provides a process for preparing shaped articles and articles prepared by such process based on a polyimide polymer, the polymer prepared by subjecting a mixture of aromatic dianhydride and aromatic diamine monomers, at least one of which contains the group ##STR1## linking two aromatic moieties, wherein R is CF.sub.3 or phenyl, to a low temperature, substantially isothermal solution polymeriazation process wherein the content of the mixed monomers in solvent is maintained within the range of from about 8 to about 12% by weight solids concentration during the polymerization process. The process is conducted for a sufficient length of time and uniformity of temperature, generally below about 35.degree. C., to achieve a weight average polyimide polymer molecular weight within the range of about 80,000 to about 135,000, more preferably of about 90,000 to about 125,000, a polyimide inherent viscosity within the range of from about 0.45 to about 0.