SHAPED ARTICLES CONTAINING COPOLYMERS OF POLYBENZAZOLES

Abstract: Granular compositions which comprise a block copolymer containing blocks of polybenzazole polymer and blocks of thermoplastic polymer can be compression molded to provide a molded article having physical properties superior to molded articles made from the thermoplastic polymer alone.

Description: SHAPED ARTICLES CONTAINING COPOLYMERS OF POLYBENZAZOLES The present invention relates to the art of polybenzazole (PBZ) polymers and polymer compositions containing blocks of those polymers. PBZ polymers, i.e., polybenzoxazole, polyben- zothiazole and polybenzimidazole, and their synthesis are described in great detail in the following patents which are incorporated by reference: Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Patent 4,703,103 (October 27, 1987); Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Patent 4,533,692 (August 6, 1985); Wolfe et al., Liquid Crystalline Poly(2,6-Benzo- thiazole) Compositions, Process and Products, U.S. Pat¬ ent 4,533,724 (August 6, 1985); Wolfe, Liquid Crystal¬ line Polymer Compositions, Process and Products, U.S. Patent 4,533,693 (August 6, 1985); Evers, Thermoxida- tively Stable Articulated p-Benzobisoxazole and p-Benzo- bisthiazole Polymers, U.S. Patent 4,359,567 (November 16, 1982); Tsai et al., Method for Making Heterocyclic Block Copolymer, U.S. Patent 4,578,432 (March 25, 1986) and 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles, 601 (J. Wiley & Sons 1988). Polybenzazole polymers, and particularly "rigid rod" PBZ polymers, are noted for high tensile strength, high tensile modulus and high thermal stability. However, many polybenzazole polymers are difficult to fabricate into useful articles. Rigid and semi-rigid polybenzazoles do not have glass transition temperatures at any temperature at which they are stable. Therefore, the polymers are ordinarily spun from solution to form fibers, which serve as reinforcement within a thermosetting matrix, such as epoxy resins, to form composites. However, the fibers and the cured composites are not moldable or thermoformable. Many moldable and thermoformable polymers are known. Exemplary polymers include thermoplastic polyamides, polyimides, polyquinolines, polyquin- oxalines, poly(aromatic ether ketones) and poly(aromatic ether sulfones). However, those polymers do not have the high tensile strength and modulus which are characteristic of polybenzazole polymers. Attempts have been made to synthesize articles which combine the processability of the thermoplastic polymer with the superior physical properties of the polybenzazole polymer. To this end, molecular composites of rigid rod polybenzazole and flexible polymers have been studied. Such molecular composites are described in numerous references, such as U.S. Patents 4,207,407; 4,377,546; 4,631,318; 4,749,753 and 4,810,735, and Hwang et al., "Solution Processing and Properties of Molecular Composite Fibers and Films," 23 Polymer Eng. & Sci. 784 (1983); Hwang et al., "Phase Relationships of Rigid Rod Polymer/Flexible Coil Poly¬ mer/Solvent Ternary Systems," 23 Polymer Eng. & Sci. 789 (1983); and Hwang et al., "Composites on a Molecular Level: Phase Relationships, Processing and Properties," B22 J. Macromol. Sci.-Phys. 231 (1983). However, polybenzazole, and particularly rigid and semi-rigid polybenzazole, are incompatible with many thermoplastic polymers. When dopes containing polybenzazole and a thermoplastic polymer are coagulated, the polybenzazole agglomerates and/or phase separates. The resulting shaped articles either have poorer properties in all directions than the corresponding thermoplastic alone, or have superior properties in one direction and inferior properties in all other directions. Such compositions are useful for fibers, but not for molded articles. What are needed are materials and processes which can be used to make molded articles containing reinforcing amounts of polybenzazole polymer which have superior properties in at least two dimensions and/or are not substantially phase separated. One aspect of the present invention is a block copolymer having (a) rigid rod or semi-rigid polybenzazole polymer blocks and (b) thermoplastic polymer blocks, characterized in that (1) each polybenzazole polymer block contains on average at least 5 mer units and less than 10 mer units; and (2) the block copolymer is thermoplastic and can be compression molded without substantial phase separation. A second aspect of the present invention is a block copolymer having (1) rigid rod or semi-rigid polybenzazole polymer blocks that contain on average at least 5 mer units per block and (2) thermoplastic polymer blocks of suitable size and proportions so that the block copolymer is flowable at a temperature below its decomposition temperature, characterized in that the block copolymer is in a solid granular form that has an average particle diameter of no more than 1000 μ. A third aspect of the present invention is a briquette containing a granular composition of the present invention. A fourth aspect of the present invention is a process for forming a shaped article comprising the step of molding a solid granular composition in a mold at a temperature at which the granular composition is flowable and at a pressure sufficient to cause the granular composition to consolidate and conform to the shape of the mold, characterized in that (1) the granular composition contains a non-phase-separated block copolymer having (a) polybenzazole polymer blocks that contain on average at least 5 mer units per block and (b) thermoplastic polymer blocks of suitable size and proportions so that the block copolymer is flowable at a temperature below its decomposition temperature; and (2) the granular composition has an average particle diameter of no more than 1000 μ. A fifth aspect of the present invention is a molded article made by the process of the present invention. Granular compositions and/or briquettes of the present invention can be used in the process of the present invention to fabricate the molded articles of the present invention. Such molded articles may be useful as structural elements, as circuit boards, or for any other purpose for which molded plastic articles are useful. The following terms, which are used repeatedly throughout this application, have the meanings and pre¬ ferred embodiments set out hereinafter unless otherwise specified. AA/BB-Polybenzazole (AA/BB-PBZ) - a polybenz- azole polymer characterized by mer units having a first aromatic group (Ar1), a first and a second azole ring fused with said first aromatic group, and a bond or a divalent organic moiety (DM) bonded by a single bond to the 2-carbon of the second azole ring. The divalent organic moiety (DM) is chosen such that does not interfere with the synthesis, fabrication or use of the PBZ polymer; it is preferably a second aromatic group (Ar2). it may, in some cases, be an alkyl group or a bond. Mer units are preferably linked by a bond from the divalent organic moiety (DM) to the 2-carbon of the first azole ring in an adjacent mer unit. Mer units suitable for AA/BB-PBZ polymers are preferably repre¬ sented by Formula 1 : wherein Z is as defined for azole rings subsequently and all other characters have the meaning and preferred embodiments previously given. AB-Polybenzazole (AB-PBZ) - a polybenzazole polymer characterized by mer units having a first aro¬ matic group and a single azole ring fused with said first aromatic group. The units are linked by a bond from the 2-carbon of the azole ring in one mer unit to the aromatic group of an adjacent mer unit. Mer units suitable for AB-PBZ polymers are preferably represented by Formula 2: wherein Z is as defined for azole rings subsequently and all other characters have the meaning and preferred embodiments previously given. Acid group (AG) - a carboxylic acid, a sulfonic acid or a derivative of such an acid, such as a halide or ester, which can react with an aromatic group by aromatic electrophilic substitution. Acid groups are preferably the acid or acid halide and more preferably a carboxylic acid or carboxylic acid chloride. o-Amino-basic moiety - a moiety, which is bonded to an aromatic group, consisting of ( 1) a primary amine group bonded to the aromatic group and (2) a hydroxy, thiol or primary or secondary amine group bonded to the aromatic group ortho to said primary amine group. It preferably comprises a hydroxy, thiol or primary amine moiety, more preferably comprises a hydroxy or thiol moiety, and most preferably comprises a hydroxy moiety. Secondary amine groups comprise an aromatic or an aliphatic group and preferably an alkyl group. The secondary amine group preferably comprises no more than about 6 carbon atoms, more preferably no more than about 4 carbon atoms and most preferably no more than about 1 carbon atom. Aromatic group (Ar) - any aromatic ring or ring system. Size is not critical as long as the aromatic group is not so big that it prevents further reactions of the moiety in which it is incorporated. Each aro¬ matic group preferably comprises no more than 18 carbon atoms, more preferably no more than 12 carbon atoms and most preferably no more than 6 carbon atoms. Each may be heterocyclic but is preferably carbocyclic and more preferably hydrocarbyl. If the aromatic group is heterocyclic, the heteroatom is preferably nitrogen. Unless otherwise specified, each aromatic group may comprise a single aromatic ring, a fused ring system or an unfused ring system containing two or more aro- matic moieties joined by bonds or by divalent moieties which are inert under polymerization conditions. Suit¬ able divalent moieties comprise, for example, a carbonyl group, a sulfonyl group, an oxygen atom, a sulfur atom, an alkyl group and/or a perfluorinated alkyl group. Each aromatic group is preferably a single six-membered ring. Each aromatic group may contain substituents which are stable in solvent acid, do not interfere with further reactions of the moiety which the aromatic group is part of, and do not undergo undesirable side reac¬ tions. Examples of preferred substituents include halo¬ gens, alkoxy moieties or alkyl groups. More preferred m ~ substituents are either an alkyl group having no more than 6 carbon atoms or a halogen. Most preferably, each aromatic group contains only those substituents specifically called for hereinafter. 15 Decoupling group (D) - a divalent moiety which links an acid group or an aromatic group to a deac¬ tivating group, such as an azole ring, a carbonyl group or a sulfonyl group, and which shields the acid group or aromatic group from the deactivation sufficiently for 20 the acid group or aromatic group to participate in an aromatic electrophilic substitution reaction. Decoupling groups typically contain, for example, an ether group, a thio group, an aliphatic group and/or an P5 aromatic group. Decoupling groups typically do not contain electron-withdrawing groups, such as carbonyl or sulfonyl groups. Decoupling groups preferably contain one or more aromatic groups that are linked by ether groups. 30 The minimum decoupling needed depends upon the group that is being shielded and the reaction conditions. Reactions carried out in a dehydrating protic acid solution require more decoupling than do reactions that are carried out in the presence of a Lewis acid. Aromatic groups that are to undergo reaction require greater decoupling than do acid groups. For instance, in the presence of a Lewis acid, acid groups can be decoupled by a single phenylene ring and aromatic groups by a single ether or thioether group. In a dehydrating protic acid solution, a decoupling group that links two acid groups preferably contains at least two aromatic groups, which are more preferably linked by an ether group; a decoupling group that links two aromatic groups preferably contains at least an aromatic group and a first ether group and more preferably contains a second ether group as well. The ether groups link the aromatic groups together. Decoupling and suitable decoupling groups are discussed in Colquhoun, "Synthesis of Polyether Ketones in Trifluoromethane Sulfonic Acid," 25 (2) Polymer Preprints 17-18 & Table II (1984); and Colquhoun et al., "Synthesis of Aromatic Polyether Ketones in Trifluoromethane Sulfonic Acid," 29 Polymer 1902 (1988). Electron-deficient carbon group (Q) - any group containing a carbon atom which can react in the solvent acid with an o-amino-basic moiety to form an azole ring, such as the groups listed in column 24, lines 59-66 of the 4,533,693 patent plus ortho esters, metal carboxylate salts, cyano groups and trihalomethyl groups. Preferred electron-deficient carbon groups are carboxylic acids and acid halides. Halogens in electron-deficient carbon groups are preferably chlo¬ rine, bromine or iodine and more preferably chlorine. Phase Separation - The existence within a coagulated article of optically distinct anisotropic domains of polymers. In shaped articles of the present invention, some phase-separation on a molecular level is inevitable, and the articles can show semicrystalline character. However, the size of domains of phase- -separated polymer in the polymer compositions of the present invention is preferably on average not greater than 1000 angstroms, highly preferably not greater than 500 angstroms, more preferably not greater than 200 angstroms, more highly preferably not greater than 100 angstroms and most preferably not greater than 50 angstroms. Phase separation may be judged by known characteristics, such as opacity, electron-microscopy, small-angle X-ray scattering or small-angle light scat¬ tering. Methods for measuring phase-separation in a system are discussed in Hwang et al., "Composites on a Molecular Level: Phase Relationships, Processing, and Properties," B22(2) J. Macromol. Sci.-Phys. 231, 234-35 (1983). Polybenzazole (PBZ) polymer - A polymer from the group of polybenzoxazoles and polybenzobisoxazoles (PB0), polybenzothiazoles and polybenzobisthiazoles (PBT) and polybenzimidazoles or polybenzobisimidazoles (PBI). For the purposes of this application, the term "polybenzoxazole (PB0)" refers broadly to polymers in which each unit contains an oxazole ring bonded to an aromatic group, which need not necessarily be a benzene ring. The term "polybenzoxazole (PB0)" also refers broadly to poly(phenylene-benzo-bis-oxazole)s and other polymers wherein each unit comprises a plurality of oxa¬ zole rings fused to an aromatic group. The same under¬ standings shall apply to the terms polybenzothiazole (PBT) and polybenzimidazole (PBI). Polybenzazole poly¬ mers used in the present invention are preferably poly- benzoxazole or polybenzothiazole, and more preferably polybenzoxazole. Rigid Rod PBZ polymer - An "intrinsic" or "ar¬ ticulated" rigid rod PBZ polymer as the terms "intrin¬ sic" and "articulated" are defined in the Hwang, "Pro¬ cessing, Structure and Properties of Liquid Crystalline PBT Polymer," Kansai Committee of the Society of Fiber Science and Technology, Japan, Post Symposium on Forma¬ tion, Structure and Properties of High Modulus and High Tenacity Fibers 23-26 (August 26, 1985); Evers et al, "Articulated All-Para Polymers with 2,6-Benzobisoxazole, 2,6-Benzobisthiazole, and 2,6-Benzobisimidazole Units in the Backbone," 14 Macromolecules 925 (1981); Evers, "Thermoxidatively Stable Articulated Benzobisoxazole and Benzobisthiazole Polymers," 24 J. Poly. Sci. Part A 1863 (1986) and Evers et al., Articulated Para-Ordered Aro¬ matic Heterocyclic Polymers Containing Diphenoxybenzene Structures, U.S. Patent 4,229,566 (October 21, 1980). Intrinsic rigid rod polymers are essentially rectilinear and are theorized to have a persistence length comparable to their contour length. They contain essentially no angles of catenation less than 150°. Articulated rigid rod polymers comprise a plurality of essentially rectilinear moieties joined by a relatively small number of moieties which are not rectilinear and have angles of catenation less than 150°. Rigid rod PBZ polymers used in the present invention are preferably intrinsic rigid rod polymers. Solvent acid - any non-oxidizing liquid acid capable of dissolving PBZ polymers, such as sulfuric acid, methanesulfonic acid, trifluoromethylsulfonic acid, polyphosphoric acid and mixtures thereof, which is suitable for carrying out azole-ring formation or acyla- tion or sulfonation reactions that form block copolymers used in the present invention. It must be sufficiently non-oxidizing that it does not substantially oxidize D AB- and BB-PBZ monomers which are dissolved therein. Solvent acids are preferably dehydrating acids, such as polyphosphoric acid or a mixture of methanesulfonic acid and phosphorus pentoxide and/or polyphosphoric acid. 1Q The optimum P2O5 content of polyphosphoric acid depends upon the stage of processing. Polyphosphoric acid that is used to make polybenzazole polymers preferably contains initially at least about 80 weight percent P2O5 and more preferably at least about 85 weight percent 15 p 2^5* ~-~- optimum P2O5 content is somewhat lower after the reactions are complete. The ratio of methanesulfonic acid to phosphorus pentoxide in mixtures of those compounds is preferably no more than 20:1 by weight; and preferably no less than 1:1, more preferably 20 no less than 5:1 by weight at the commencement of a reaction. However, certain solvent acids, such as trifluoromethanesulfonic acid, are suitable for carrying out Friedel-Crafts acylation or sulfonation reactions 2~- even though they do not contain a dehydrating component, such as phosphorus pentoxide. The present invention uses thermoplastic block copolymers containing blocks of rigid rod or semi-rigid 30 polybenzazole polymer and blocks of thermoplastic polymer. Some suitable block copolymers and processes to make them are described in detail in Harris et al., Copolymers Containing Polybenzoxazole, Polybenzothiazole and Polybenzimidazole Moieties, International Application No. PCT/US89/04464 (filed October 6, 1989), - 13- International Publication No. WO 90/03995 (published April 19, 1990) and in Harris et al., Thermoplastic Compositions Containing Polybenzoxazole, Polybenzo- thiazole and Polybenzimidazole Moieties and Process for Making Shaped Articles from Them, EP0 Application 90104963.5 (filed March 16, 1990), EPO Publication 0 388 803 (published September 26, 1990).. Rigid and Semirigid Polybenzazole Blocks Rigid and semi-rigid polybenzazole blocks are well-known. The rigid or semi-rigid polybenzazole block is most preferably a rigid rod block. Rigid and semirigid polybenzazole homopolymers typically are not thermoplastic and typically form liquid crystalline solutions when dissolved at relatively high concentration in a solvent. Mer units that are suitable to make rigid and semirigid polybenzazole mer units are well known in the art. The rigid or semi-rigid polybenzazole block may contain AB-PBZ mer units or AA/BB-PBZ mer units or both, as those units are previously defined and depicted. It preferably contains AA/BB-PBZ mer units and more preferably consists essentially of AA/BB-PBZ mer units. In semi-rigid AB-PBZ mer units, the aromatic group (Ar) is preferably either (1) a trivalent benzene ring having the single bond to the 1-position and the azole ring fused to the 3- and 4-positions; or (2) a trivalent biphenyl group having the single bond to the 4-position and the azole ring fused to the 3'- and 4'-positions. In rigid AA/BB-PBZ mer units, the first aromatic group (Ar') is preferably a tetravalent benzene or naphthalene ring having azole rings fused in the 1,2- and 4,5- positions. The divalent organic moiety (DM) is preferably a 1 ,4-phenylene moiety, a 4,4'-biphenylene moiety or a 2,5-pyridenylene moiety. The rigid or semirigid polybenzazole block may contain a small number of non-rigid mer units so as to form an "articulated" semirigid structure. The rigid or semi-rigid polybenzazole block may contain polybenzoxazole, polybenzothiazole, and/or polybenzimidazole mer units (Z = -0-, -S- or -NR- respectively). It preferably consists essentially of polybenzoxazole and/or polybenzothiazole mer units (Z = -0- or -S-). It more preferably consists essentially of polybenzoxazole mer units (Z = -0-). Examples of the most preferred mer units for the rigid or semirigid polybenzazole block are set out in the following Formulae: Each rigid or semirigid polybenzazole block contains on average at least 5 mer units and preferably at least 8 mer units. Each rigid or semirigid block preferably contains on average at most 150 mer units, more preferably at most 100 mer units, and most preferably at most 50 mer units. Theoretically, block copolymers having larger rigid or semi-rigid polybenzazole blocks, such as at least 10-20 mer units on average, should ordinarily have higher tensile strength and modulus than polymers having smaller average rod lengths, such as 5-10 mer units. However, the block copolymers containing smaller polybenzazole segments are frequently more flowable and easier to obtain complete consolidation under molding conditions. Thus, the molded article made under particular molding conditions from block copolymer having a smaller average rod length may have better physical properties. Thermoplastic Blocks The thermoplastic block contains a polymer that is stable in a solvent acid. The polymer must be able to be linked to the polybenzazole block either by polymerizing in a solvent acid solution containing the polybenzazole blocks or by polymerization in a separate medium and subsequent linking of the blocks by reaction of end groups in a solvent acid. The thermoplastic block may contain a thermoplastic polybenzazole polymer, or a thermoplastic acid soluble polymer that is not a polybenzazole, or a random or sequential copolymer that contains both mer units of a polybenzazole polymer and mer units of a thermoplastic acid soluble polymer that is not a polybenzazole. The thermoplastic blocks preferably have an average formula weight of at least about 800. Their degree of polymerization is preferably at least about 10 and more preferably at least about 20. (A) Thermoplastic Polybenzazoles Thermoplastic polybenzazole polymers are known and are described in Harris et al., Thermoplastic Compositions Containing Polybenzoxazole, Polybenzo¬ thiazole and Polybenzimidazole Moieties and Process for Making Shaped Articles from Them, EPO Application 90104963.5 (filed March 16, 1990), EPO Publication 0 388 803 (published September 26, 1990) and in K.-U. Bϋhler, Spezialplaste 838-866 (Akademie-Verlag 1978). They are neither rigid nor semirigid polymers, and they typically do not form liquid crystalline solutions. They can be described as falling roughly into two groups: aliphatic polybenzazoles and jointed polybenzazoles. Jointed polybenzazoles are preferably represented by the Formula: wherein: X is a bond or the first divalent linking moiety; each kv- is an aromatic group; L is a non-linear group that is stable under conditions at which the polymer is synthesized, fabricated and used; and all other characters have the meanings previ¬ ously assigned. Each non-linear group (L) may contain: (a) a meta-aromatic group (Ar m ), such as an m-phenylene moiety, an m-pyridinylene moiety, a 3,4'-biphenylene moiety, a 3,3'-biphenylene moiety or a 2,6-naphthalene moiety; or (b) an aliphatic moiety; or (c) two aromatic groups (Ar) linked by a second divalent linking moiety (X'). The aromatic groups have the descriptions and preferred embodiments previously defined for aromatic groups. The first and second divalent linking moieties (X and X') may be any nonlinear divalent moiety that is stable under conditions at which the polymer is synthesized, fabricated and used. Each is preferably independently a sulfonyl moiety, an oxygen atom, a sulfur atom or an aliphatic group. Each is more preferably either a sulfonyl moiety or an oxygen moiety. Most preferably, the first divalent linking moiety (X) is a sulfonyl moiety and the second divalent linking moiety (X') is an oxygen atom. It is within the scope of the present invention for either or both divalent linking moieties to comprise two oxygen atoms, sulfur atoms, sulfonyl moieties or aliphatic moieties linked by an aromatic group. When the non-linear group (L) or a first or second divalent linking moiety (X or X') contains an aliphatic group, the aliphatic group preferably comprises no more than about 12 carbon atoms. The aliphatic group may be cyclic or branched. It is preferably alkyl or halogenated alkyl. Examples of suitable aliphatic groups include a 1,2-cyclohexyl moiety and a perfluoroisopropylidene moiety. Due to the high glass transition temperatures of jointed polybenzazole polymers, aliphatic moieties within jointed polybenzazole polymers are preferably perfluorinated, such as perfluoroisopropylidene, to add temperature stability. Mer units in jointed polybenzazole are more preferably represented by Formula 5(a) 5(a) and are most preferably represented by Formula 5(b) 5(b) or the variation thereof wherein the sulfonyl group is meta to the Z groups and para to the nitrogen atoms. Aliphatic polybenzazoles contain an aliphatic linkage in the polymer backbone. The polymers may be AB-PBZ polymers, but they are preferably AA/BB-PBZ polymers. Mer units within aliphatic polybenzazole polymers are preferably represented by one of Formulae 6(a) and (b) wherein Ar is the aromatic group as previously described, R^ is an aliphatic group that contains at least about 3 carbon atoms, and all other characters have the meanings previously assigned. The size of the aliphatic group (R') is not critical. The aliphatic group preferably contains no more than about 12 carbon atoms, more preferably no more than about 10 carbon atoms and most preferably no more than about 8 carbon atoms. It may be cyclic or branched, but is preferably linear. It must be stable under conditions at which the block copolymer is synthesized, fabricated and used. The aliphatic group may be fluorinated for better thermal stability. The aliphatic group is highly preferably alkyl or perfluoroalkyl. The bonds that link the aliphatic group with the polymer backbone are preferably not to the same carbon atom or to adjacent carbon atoms. Aliphatic AB-PBZ polymer blocks can be syn¬ thesized by known processes, such as by (1) formation of the corresponding amide in a system of triphenyl phos- phine, hexachloroethane and pyridine and (2) thermal cyclization of the amide, as described in Mathias et al., "Two-Step Synthesis of Alkyl- and Alkenyl- benzoxazole Polymers," 18 Macromolecules 616 (1985). Aliphatic AA/BB-PBZ polymer blocks can be synthesized by known processes, such as by reacting a BB-PBZ monomer with an AA-PBZ monomer that contains an aliphatic group bonded to two electron-deficient carbon groups, as described in U.S. Patent 4,533,693. The block copolymers may be synthesized by known processes. The rigid or semi-rigid blocks and the thermoplastic blocks may be synthesized separately with end groups that are later reacted to link the blocks into a block copolymer. Alternatively, one set of blocks may be formed in a reaction mixture, and then the monomers for a second block copolymer may be added to the mixture and the reaction may be continued to form the block copolymer. (B) Thermoplastic Non-Polybenzazole Polymers and Copolymers Other suitable thermoplastic polymers include polyamide, thermoplastic polyimide, polyquinoxaline, 5. polyquinoline, poly(aromatic ether ketone) and/or a poly(aromatic ether sulfone), or a copolymer of those polymers with each other and/or polybenzazole. The more preferred polymers are polyamide, poly(aromatic ether ketone) or poly(aromatic ether sulfone) or a copolymer TO with each other and/or polybenzazole. Suitable thermoplastic blocks are described in International Publication No. WO 90/03995 (published April 9, 1990) at pp. 73-102. 15 Polyamide polymers used in the present invention are usually represented by one of the Formulae: 20 wherein A' and k~ are divalent organic moieties that do not interfere with the synthesis, fabrication or use of the block copolymer and that are selected so that the polyamide block is thermoplastic. Each divalent organic moiety (A' and k ~ ) may contain an aromatic group, but preferably at least one is an aliphatic group. Aliphatic divalent organic moieties preferably comprise no more than about 12 carbon atoms and more preferably no more than about 6. Aliphatic divalent organic 5 moieties are preferably saturated and more preferably alkyl. Most preferably, the first divalent organic moiety (A^) is aromatic, and the second (A 2 ) is aliphatic. 10 Poly(aromatic ketones) and poly(aromatic sul¬ fones) are preferably represented by one of Formulae 8(a) or (b) 15 8(a) -fAr-D-Ar-Y-)- b 8(b) fAr-D-Ar-Y-T-Y-)- b wherein 20 each Ar is independently an aromatic group, each D independently is a decoupling pc - group as previously defined, each Y is independently a sulfonyl or carbonyl group, T is a divalent organic moiety, and b is a number of repeating mer units 30 greater than 1. Poly(aromatic ketones or sulfones) are more preferably represented by one of Formulae 8(c) or (d): 8(c) -(-fAr-J) n -Ar-Y* b 8(d) -H-Ar-J^ n -Ar-Y-T-Y b wherein n is a number of repeating units equal to 1 or more and each J is individually an oxygen atom, a sulfur atom or a bond chosen such that at least one J is an oxygen or a sulfur atom. Each J is more preferably an oxygen atom or a bond chosen such that at least one J is an oxygen atom. Each n is more preferably at least 2. Each divalent organic moiety (T) must be stable in solvent acid, preferably up to at least about 50°C, more preferably up to at least about 100°C and most preferably up to at least about 200°C. Each divalent organic moiety (T) preferably comprises an aromatic group and more preferably consists essentially of an aromatic group or a plurality of aromatic groups linked by sulfur or oxygen atoms. Aromatic groups are most preferably meta- or para-phenylene groups. Copolymers of polyamide or poly(aromatic ether) with polybenzazole are structurally similar to the homopolymers, except that at least one divalent moiety within the structure (either A1, A2, Ar or T) is replaced with two aromatic groups that are linked by a benzazole or benzo-bis-azole moiety. Such copolymers are preferably polybenzazole-pol (aromatic ether) copolymers. Exemplary copolymers are described in Dahl et al., Aromatic Polyether Ketones Having Imide, Amide, Ester, Azo, Quinoxaline, Benzimidazole, Benzoxazole or Benzothiazole Groups and a Method of Preparation, International (PCT) application W086/02368 (published April 24, 1986), and in Harris et al., Copolymers Containing Polybenzoxazole, Polybenzothiazole and Polybenzimidazole Moieties, International Application No. PCT/US89/04464 (filed October 6, 1989), International Publication No. WO 90/03995 (published April 19, 1990). The copolymers are preferably represented by the Formula: They are more preferably represented by the Formula: 9 ( b ) They are most preferably represented by the Formula: 9(c) Each character in those Formulae has the meaning and preferred embodiments previously given. The thermoplastic blocks may be synthesized in a manner that is ordinary for the particular type of polymer selected. The thermoplastic polymer blocks may be linked to the rigid or semirigid polybenzaozle block either (i) by reaction of an o-amino-basic moiety and an electron-deficient carbon group to form of an azole ring; or (ii) by Friedel-Crafts reaction of an aromatic group and an acid group to form a carbonyl or sulfonyl group bonded to the aromatic group. Both reactions may be carried out in a dehydrating solvent acid, such as polyphosphoric acid or methanesulfonic acid/P2θ5. The end groups of the blocks should be selected so that they can react in such an environment. Block Copolymers and Their Use The proportions of polybenzazole block to thermoplastic block are chosen so that the entire block copolymer is thermoplastic. The block copolymer may contain between -1 percent and 99 percent thermoplastic block by weight. It preferably contains at least 10 percent thermoplastic block by weight, more preferably contains at least 30 percent thermoplastic block by weight, and most preferably contains at least 70 percent thermoplastic block by weight. It preferably contains at least 3 percent rigid or semirigid polybenzazole block by weight and more preferably contains at least 5 percent rigid or semirigid polybenzazole block by weight. The block copolymer should become flowable at a temperature at which it does not substantially decompose. Block copolymers containing higher proportions of rigid or semirigid polybenzazole may frequently provide superior physical properties as fabricated, but block copolymers containing lower proportions of poly¬ benzazole may be more flowable and thus may consolidate better to provide a molded article having superior properties. The proportions of rigid or semirigid polybenzazole block to thermoplastic block are preferably chosen such that the block copolymer flows 10 and the granular composition consolidates during molding to provide a molded article having physical properties superior to molded articles made from the thermoplastic homopolymer alone. Those optimum proportions varies depending upon the specific polymers and block sizes 15 used in the block copolymer, but can readily be determined experimentally by persons of ordinary skill in the art. The average molecular weight of the block 20 copolymer as a whole also affects the flowability of the block copolymer. The average molecular weight should be kept low enough that the granular composition consolidates during molding to provide a molded article pt - having physical properties superior to molded articles made from the thermoplastic homopolymer alone. Molecular weight may be regulated either by adjusting the stoichiometry of the reaction or by use of a chain terminator. Many different monofunctional reagents may 30 be used as chain terminators, as described in U.S. Patent 4,703,103, which is incorporated herein by reference, but monofunctional aromatic carboxylic acid derivatives such as benzoic acid and benzoyl chloride are preferred. The optimum average molecular weight varies depending upon the specific polymers, block sizes and proportions of blocks used in the block copolymer, but can readily be determined experimentally by persons of ordinary skill in the art. Compositions and molded articles of the present invention may consist essentially of a block copolymer as previously described. Alternatively, compositions and molded articles of the present invention may contain thermoplastic polymers or polybenzazole polymers which are not part of a block copolymer, or both. The polymers are preferably selected such that the physical properties of the molded composition are superior to physical properties of the thermoplastic polymer alone, in at least two dimensions. The polymers are more preferably selected such that the composition does not experience substantial phase separation during coagulation or molding. If the composition contains a thermoplastic polymer, it is preferably a homopolymer or copolymer having a structure similar to the thermo¬ plastic blocks of the block copolymer. The concentra¬ tion of polybenzazole polymer in the composition should be low enough that the composition is moldable. The proportions of rigid or semirigid polybenzazole outside of block copolymers are preferably minimized. The composition most preferably contains no rigid or semirigid polybenzazole outside of the block copolymer. The block copolymers and polymer compositions containing them are ordinarily formed in a solvent acid solution or dope, from which they may be coagulated by contacting the dope with a non-solvent diluent such as water. The dope must ordinarily be in an optically isotropic (non-liquid crystalline) state when coagulated in order to form a coagulated product which is at least planar isotropic (isotropic in two dimensions) and is more preferably isotropic in three dimensions. The coagulated product is most preferably not optically phase separated. Liquid crystalline dopes tend to form phase separated and anisotropic coagulated products. Optical isotropy and anisotropy of the dope can be determined by a number of tests familiar to persons of ordinary skill in the art, such as those described in - Hwang et al., "Composites on a Molecular Level: Phase Relationships, Processing, and Properties," B22(2) J. Macromol. Sci.-Phys. 231, 234-35 (1983). A simple method is to see if the solution exhibits birefringence when viewed under a microscope under cross-polar 5 conditions. Within even optically isotropic solutions, some association of rigid rod blocks is likely on a molecular scale. However, in polymers precipitated from the optically isotropic phase, the level of anisotropy and phase-separation is preferably small enough to 0 provide a block copolymer or polymer composition which is essentially a molecular composite. The point at which a given dope changes from ~ optically isotropic to anisotropic phase and the reverse varies as a function of many factors, such as the con¬ centration of the polymer, the solvent, the size and concentration of rigid rod PBZ blocks within the poly¬ mers in the dope, the temperature of the dope and other 0 factors. The parameter most easily controlled is con¬ centration of the block polymer and any homopolymer. It is convenient to synthesize the block copolymer in a solution having a low enough concentration to avoid the anisotropic phase. If an anisotropic dope is formed, it may be diluted with solvent acid until an optically isotropic state is reached. The preferred concentration of polymer in optically isotropic dopes of the present invention varies depending upon the portion of the polymer which is rigid rod PBZ. If the polymer in the dope contains only 5 weight percent rigid rod PBZ block or less, then the concentration of polymer in the dope may be as high as the solvent acid can dissolve, such as 50 weight percent or less. If the polymer contains 30 weight percent rigid rod PBZ block, then the dope preferably comprises no more than 15 weight percent polymer. If the polymer contains 50 weight percent rigid rod PBZ block, then the dope preferably comprises no more than 10 weight percent polymer. If the polymer comprises 70 weight percent rigid rod PBZ block, then the dope preferably comprises no more than 6 weight percent polymer and more preferably no more than 4 weight percent polymer. The solvent acid in the dope has the definition and preferred embodiment previously given for solvent acids. It is most conveniently the solvent acid in which the block copolymer was synthesized. However, the block copolymer may be synthesized in a first solvent acid such as polyphosphoric acid, coagulated, and redissolved in a second solvent acid such as methanesulfonic acid. The dope may also contain other additives that precipitate with the polymers, such as stabilizers or coloring agents. Preferably, such additives are minimized. The polymer is recovered from the dope by contacting the dope with a non-solvent which causes the block copolymer to coagulate. The non-solvent is preferably aqueous. The non-solvent may be basic or slightly acidic, but is preferably neutral at the commencement of its use. Of course, the non-solvent bath may become progressively more acidic as it coagulates more dope unless the non-solvent in the bath has a reasonably steady flow of non-solvent to and from the bath or a pH adjusting material is added. Large coagulated particles of block copolymers and compositions containing them may be difficult to grind or pulverize to make granular compositions of the present invention. Therefore, it is preferable to coagulate the dope directly in a granular form. This can be carried out by a number of processes. For instance, the dope may be frozen. The dope is preferably frozen at a temperature less than 0°C, more preferably' at most -78°C, more highly preferably at most -150°C and most preferably at most -190°C. A convenient temperature is liquid nitrogen temperature. The frozen dope is more easily ground than is the coagulated polymer and may be ground on ordinary grinding equipment suitable for grinding the frozen solvent acid, such as a ball mill or attrition mill. The ground dope is then placed in a relatively warmer non-solvent bath, which causes the dope to melt and the polymer to coagulate. The bath must be at a temperature above the freezing point of the dope. It is preferably at a temperature of at least 10°C, and is more preferably at a temperature no higher than 50°C. The temperature is conveniently room temperature. Freeze- -grinding and apparatuses to carry it out are described in the following U.S. Patents: 2,216,094; 2,836,368; 3,453,221; 3,868,997; 4,069,161; 3,936,517; 3,614,001; 3,658,259; 3,713,592; 3,771,729; 4,072,026; and 4,273,294. Alternatively, the dope may be sprayed in a fine mist into a coagulation bath. The coagulation bath is preferably agitated or otherwise in motion. The powders resulting from either method are preferably filtered, washed, and dried in order to recover the granular composition. Spray extraction of polymers and equipment for carrying it out are described in the following U.S. Patents: 3,953,401; 4,100,236; 4,206,161 and 4,469,818. The resulting granular product should have an average particle size small enough to be molded into a solid article. The average particle diameter is preferably no more than 500 μ, more preferably no more than 100 μ, more highly preferably no more than 50 μ, and most preferably, no more than 10 μ. The particles are preferably homogeneous, having approximately the same mixtures and proportions of polymers as were found in the dope. Polymer within the particles is preferably isotropic in at least two dimensions (planar isotropic), and is more preferably isotropic in three dimensions. Granular compositions of the present invention may be molded as they are, but they are conveniently pressed to form a briquette for easier handling. The briquette is formed by subjecting the powder to a pressure high enough to press it together so that it will not fall apart again when pressure is released. The pressure is preferably at least 50 psi, more preferably at least 500 psi, and most preferably at least 2000 psi. The preferred size of the briquette is limited primarily by practical considerations. It must be of an appropriate size for the mold in which it will be used. If it is too large there may be difficulty in pressing a single briquette from the powder. 10 The granular composition of the present invention, whether in granular or briquette form, may be molded by heating under pressure in a mold. The mold may be as simple as two heated platens for making a flat 15 plaque or may be complex, such as the shape of a part, etc. The granular composition may be molded in the mold alone, or fibers may be intermixed with the granular composition such that the resulting molded product is a fiber reinforced composite. Examples of suitable fibers 20 include aramid fibers, carbon fibers, glass fibers, ceramic fibers, quartz fibers and polybenzazole fibers. The granular composition may also be molded in a mixture with granular additives, such as stabilizers, fillers, pc - coloring agents, rubber modifiers or other additives. The temperature and pressure of molding are chosen so that the individual particles of the granular composition fuse to form a single article. Optimum 30 temperature, pressure and time of molding necessarily depend upon the flowability of the polymers in the granular composition. Copolymers that contain longer rigid or semi-rigid segments, contain higher concentrations of rigid and semi-rigid segments and have higher average molecular weights ordinarily require higher molding temperatures and pressures and longer molding times than similar copolymers that contain shorter rigid or semi-rigid segments, contain lower concentrations of rigid and semi-rigid segments and/or have lower average molecular weights. The temperature should be at least the glass transition temperature of the granular composition. It is preferably at least 5 to 10°C above the glass transition temperature of the granular composition. It should also be below the temperature at which substantial decomposition occurs in the granular composition. The preferred temperatures are highly dependent upon the chemical and physical make-up of the granular composition. For block copolymers having no less than 75 percent of either poly(aromatic ether ketone) block or polybenzoxazole/poly(aromatic ether ketone) block, the temperature is preferably at least 250°C, more preferably at least 325°C and most preferably at least 350°C. For block copolymers having no less than 75 percent of amorphous polyamide block, the temperature is preferably at least 100°C and more preferably at least 150°C. For granular compositions containing jointed polybenzazole as the thermoplastic portion of the block copolymer, the molding temperature is preferably at least 200°C, more preferably at least 250°C, and most preferably at least 350°C. For granular compositions containing aliphatic polybenzazole as the thermoplastic portion of the block copolymer, the molding temperature is preferably at least 200°C, more preferably at least 230°C, and most preferably at least 270°C. For granular compositions containing jointed polybenzazole as the thermoplastic portion of the block copolymer, the molding temperature is preferably at most 500°C, more preferably at most 475°C, and most preferably at most 450°C. For granular compositions containing aliphatic polybenzazole as the thermoplastic portion of the block copolymer, the molding temperature is prefer¬ ably at most 400°C, more preferably at most 350°C, and most preferably at most 300°C. Optimum temperatures for each granular composition may be determined without undue experimentation by persons of ordinary skill in the art. The pressure may be any pressure at which individual particles in the granular composition will fuse and consolidate to form a single article. Preferred pressure is also dependent upon the physical and chemical make-up of the granular composition and upon the temperature at which molding occurs. The pressure is preferably as low as is necessary to obtain sufficient consolidation of the powder to make a molded product. Fo block copolymers containing at least 75 percent of thermoplastic polymer block, the pressure is preferably no more than 50,000 psi, more preferably no more than 10,000 psi and most preferably no more than 5000 psi. To obtain good consolidation the pressure is ordinarily at least 50 psi, more typically at least 500 psi and most often at least 1000 psi. Optimum pressure may be determined by persons of ordinary skill in the art without undue experimentation. The molded article may optionally be annealed after it is molded. The annealing preferably takes place at a temperature above the glass transition temperature of the polymer in the molded article, but below its melting point. Annealing more preferably takes place at a temperature close to the melting point of the polymer. Annealing may take place at sub- atmospheric or supratmospheric pressures, but is conveniently at ambient pressure. The atmosphere for annealing is preferably air or nitrogen, but may be any other atmosphere in which the polymer is essentially stable under annealing conditions. Annealing typically causes an increase in the tensile strength of the molded article, but may also cause a slight decrease in the tensile modulus of the molded article. The product of the molding process is a molded article containing the block copolymers previously described, wherein the granules of the granular composition are fused together. The fusion of individual particles may be less than perfect and complete, but the molded article is preferably almost void free (less than 1 percent void space). The polymer in the molded article is preferably at least optically planar isotropic and more preferably optically isotropic in all dimensions. The molded article may exhibit some crystalline zones. The molded article preferably has physical properties which are superior to the physical properties of similar molded articles that contain only polymers similar to the thermoplastic block of the block copolymer. For instance, the molded article may have higher tensile strength, tensile modulus, flexural modulus, flexural strength, dimensional stability and/or solvent resistance. The improvement in properties is preferably exhibited in at least two perpendicular dimensions and more preferably in all directions. In other words, the improvement is at least biaxial, rather than uniaxial. The improvement in properties need not be uniform in all directions, but it preferably is uniform. The molded article is preferably not optically phase separated. It is not a fiber. It preferably has a thickness of at least 10 mil, and more preferably at least 1/8 inch. The maximum thickness is limited primarily by practical considerations, such as scale of equipment and the ability to heat the sample to a proper temperature throughout. It may be used as a structural material or as an electronic substrate or for any other use in which a thermoplastic polymer corresponding to the thermoplastic portion of the block copolymer would have been suitable. Illustrative Examples The following examples are given to illustrate the invention and should not be interpreted as limiting it in any way. Unless stated otherwise, all parts and percentages are given by weight. Example 1 - Granular compositions containing (a) a block copolymer of 50 percent cis-polybenzoxazole and 50 percent amorphous polyamide, and (b) amorphous polyamide, and molded articles made from them Dopes are synthesized containing (a) a block copolymer of rigid rod cis-polybenzoxazole and amorphous polyamide; and (b) an amorphous polyamide polymer. The solvent acid of the dope is a mixture of methanesulfonic acid, polyphosphoric acid and phosphorus pentoxide. The cis-polybenzoxazole blocks in the block copolymer have the calculated number average of mer units shown in Table 1 and the inherent viscosity (before incorporation into the block copolymer) shown in Table 1 , as measured in methanesulfonic acid at 25°C and 0.05 g/dL concentration. The amorphous polyamide blocks in the block copolymer are the product of reacting hexa- methylene diamine with a mixture containing 30 percent terephthaloyl chloride and 70 percent isophthaloyl chloride and appropriate amounts of 4-phenoxyphenoxy- benzoyl chloride. The block copolymer is synthesized by (1) end- -capping the polybenzoxazole block with decoupled carboxylic acid halide; (2) contacting it with polyamide that is end-capped with decoupled aromatic groups; and (3) reacting essentially equivalent moles and weights of the end-capped polymers in dehydrating solvent acid under conditions such that aromatic electrophilic substitution occurs. The process is described in detail in Harris et al., Copolymers Containing Polybenzoxazole, Polybenzothiazole and Polybenzimidazole Moieties, International Application No. PCT/US89/04464 (filed October 6, 1989), International Publication No. WO 90/03995 (published April 19, 1990) and in U.S. Patent Application Serial No. 407,973 (filed September 15, 1989). The resulting block copolymer contains about 50 percent by weight cis-polybenzoxazole and about 50 percent by weight amorphous polyamide, and has the inherent viscosity shown in Table 1, as measured in methanesulfonic acid at 25°C and 0.05 g/dL - concentration. An amorphous polyamide sold under the trademark of Selar-PA IU by E.I. DuPont de Nemours & Co. is added to each dope until the total weight proportions of poly- 5 benzoxazole to polyamide in each dope (counting both polyamide in the block copolymer and polyamide not in the block copolymer) is about 15 percent polybenzoxazole to 85 percent amorphous polyamide. The resulting dopes are optically isotropic (not liquid crystalline). The 0 total concentration of amorphous polyamide and block copolymer in the dope is 4 weight percent. Each dope is frozen at a temperature between c -190°C and -200°C, and ground to a particle size distribution between 10 μ and 2000 μ. The ground frozen dopes are added to an agitated water bath at about room temperature. The resulting precipitated granular compositions are filtered, washed and dried. They have 0 a particle size distribution between 1 μ and 250 μ. About 6 grams of each powder is pressed under 20,000 psi pressure at room temperature for about 10 seconds to form a briquette. Each briquette is molded at the temperature and pressure shown in Table 1 for the time shown in Table 1 to form a disk having a thickness of about ι6-inch (0.16 cm) and a diameter of about 2j-inches (6.4 cm). Each disk is tested for flexural strength and modulus by the test described in ASTM D-790. It has the strength, modulus and strain shown in Table 1. TABLE 1 * - not measured 1 - 1 ksi = 100 psi Example 2 - Granular compositions containing a block copolymer of 10 percent cis-polybenzoxazole and 90 percent poly(aromatic ether ketone), and molded articles made from them Dopes are formed containing 10 weight percent cis-polybenzoxazole and 90 weight percent poly(aromatic ether ketone). The solvent acid of the dope is a mixture of methanesulfonic acid, polyphosphoric acid and phosphorus pentoxide. The cis-polybenzoxazole blocks in the block copolymer have the calculated average number of mer units shown in Table 2 and the inherent viscosity (before incorporation into the block copolymer) shown in Table 2, as measured in methanesulfonic acid at 25°C and 0.05 g/dL concentration. The poly(aromatic ether ketone) blocks in the block copolymer are the product of reacting oxy-bis-(4-benzoyl chloride) with 1 ,4-diphenoxybenzene. The block copolymer is synthesized by (1) end- -capping the polybenzoxazole block with decoupled carboxylic acid halide; (2) reacting the polybenzoxazole block terminated by a decoupled acid group with oxy-bis-(4-benzoyl chloride) and 1,4-diphenoxybenzene and benzoic acid (a terminator) under conditions such that aromatic electrophilic substitution occurs. The process is described in detail in Harris et al., Copolymers Containing Polybenzoxazole, Polybenzothiazole and Polybenzimidazole Moieties, International Application No. PCT/US89/04464 (filed October 6, 1989), International Publication No. WO 90/03995 (published April 19, 1990) and in U.S. Patent Application Serial No. 407,973 (filed September 15, 1989). The resulting block copolymer composition contains about 10 percent by weight cis-polybenzoxazole and about 90 percent by weight poly(aromatic ketone), and has the inherent viscosity shown in Table 2, as measured in methane¬ sulfonic acid at 25°C and 0.05 g/dL concentration. Its concentration in the dope is about 8 weight percent. The resulting dopes are optically isotropic (not liquid crystalline) . Each dope is frozen at a temperature between -190°C and -200°C, and ground to a particle size distribution between about 10 μ and 2000 μ. The ground frozen dopes are added to an agitated water bath at about room temperature. The resulting precipitated granular compositions are filtered, washed and dried. Some granular compositions are also extracted with acetone or acetyl acetone. The granular compositions have a particle size distribution between about 1 μ and 250 μ. About 6 grams of each powder is pressed under about 20,000 pressure at room temperature for about 10 seconds to form a briquette. Each briquette is molded at the temperature and pressure shown in Table 2 for the time shown in Table 2 to form a disk having a thickness of about 1/-|6-inch (0.16 cm) and a diameter of about 2 2 -inches (6.4 cm). Each disk is tested for flexural strength and modulus by the test described in ASTM D-790. It has the strength, modulus and strain shown in Table 2. Table 2 Table 2 (continued) Table 2 (continued) Table 2 (continued) * . not measured 1 1 ksi = 1000 psi 2 terminator was benzoic acid, expressed as a mole percentage of diphenoxybenzene 3 sintered at 350°C for 1245 minutes 6 annealed at 300°C for 960 minutes in air after molding 7 annealed at 300°C for 240 minutes in air after molding 8 annealed at 300°C for 240 minutes in nitrogen after molding 9 annealed at 340°C for 240 minutes in air after molding 10 - annealed at 340°C for 240 minutes in nitrogen after molding 11 - annealed at 340°C for 960 minutes in air after molding Example 3 - Granular compositions containing a block copolymer of cis-polybenzoxazole and a thermoplastic polybenzoxazole/poly(aromatic ether ketone) copolymer, and molded articles made from them Dopes are formed containing cis-polybenzoxazole and thermoplastic polybenzoxazole/poly(aromatic ether ketone) copolymer in the proportions shown in Table 3 * The solvent acid of the dope is a mixture of methanesulfonic acid, polyphosphoric acid and phosphorus pentoxide. The cis-polybenzoxazole blocks in the block copolymer have the calculated average number of mer units shown in Table 3 and the inherent viscosity (before incorporation into the block copolymer) shown in Table 3, as measured in methanesulfonic acid at 25°C and 0.05 g/dL concentration. The polybenzoxazole/(aromatic ether ketone) blocks in the block copolymer are the product of reacting 4,6-diaminoresorcinol, oxy-bis- -(4-benzoyl chloride) and 1,4-bis-(phenoxy)benzene in a molar ratio of about 1:2:1. The block copolymer is synthesized by ( 1) reacting the polybenzoxazole oligomer and 4,6-diamino- resorcinol with 2 moles of oxy-bis-(4-benzoyl chloride) per mole of oligomer and 4,6-diaminoresorcinol combined; (2) reacting the product of step 1 with about 1 mole of 1 ,4-bis(phenoxy)benzene per mole of oligomer and 4,6- -diaminoresorcinol combined and with benzoic acid (a terminator) under conditions such that aromatic electrophilic substitution occurs. The process is described in detail in Harris et al., Copolymers Containing Polybenzoxazole, Polybenzothiazole and Polybenzimidazole Moieties, International Application No. PCT/US89/04464 (filed October 6, 1989), International Publication No. WO 90/03995 (published April 19, 1990) and in U.S. Patent Application Serial No. 407,973 (filed September 15, 1989). The resulting block copolymer composition has the calculated average structure illustrated in Formula • m 10: 10 wherein: a is a number of mer units in the rigid rod polybenzazole blocks corresponding on average 30 to the figures provided in Table 3; b is a number of mer units in the thermo¬ plastic block chosen such that on average the weight ratio of rigid rod polymer to thermoplastic polymer corresponds to the ratio given in Table 3; c is an number of repeating units such that the block copolymer has on average a molecular weight corresponding to the inherent viscosity in Table 3; and d is number of repeating units within each mer unit of the thermoplastic block which averages about 1. It contains the percentages of each polymer and has the inherent viscosity shown in Table 3, as measured in methanesulfonic acid at 25°C and 0.05 g/dL concentra¬ tion. Its concentration in the dope is between 1 and 15 weight percent. The resulting dopes are optically isotropic (not liquid crystalline). Each dope is frozen at a temperature between -190°C and -200°C, and ground to a particle size distri¬ bution between about 10 μ and 2000 μ. The ground frozen dopes are added to an agitated water bath at about room temperature. The resulting precipitated granular compositions are filtered, washed and dried. Some granular compositions are further extracted with acetone or acetyl acetone. They have a particle size distri- bution between about 10 μ and 2000 μ. About 9 grams of each powder is pressed under 20,000 psi pressure at about room temperature for about 10 seconds to form a briquette. Each briquette is molded at the temperature and pressure shown in Table 3 for the time shown in Table 3 to form a disk having a thickness of about 1/i -inch (0.16 cm) and a diameter of about 2£-inches (6.4 cm). Each disk is tested for flexural strength and modulus by the test described in ASTM D-790. It has the strength, modulus and strain shown in Table 3. Table 3 Table 3 (continued) Table 3 (continued) * not measured 1 1 ksi = 1000 psi 2 terminator was benzoic acid, using mole percentage relative to diaminoresorcinols 4 under vacuum 5 annealed at 350°C for 960 minutes after molding Example 4 - Granular compositions containing a block copolymer of cis-polybenzoxazole and a thermoplastic polybenzoxazole/poly(aromatic ether ketone) copolymer, and molded articles made from them Example 3 is repeated, except that the ratios of 4,6-diaminoresorcinol, oxy-bis-(4-benzoyl chloride) and 1 ,4-bis-(phenoxy)benzene are adjusted so that the resulting block copolymer is represented by Formula 3, wherein d averages 0.33 (the poly(aromatic ether ketone) content of the thermoplastic block is increased). The results are reported in Table 4. Table 4 * not measured 1 1 ksi = 1000 psi 2 terminator was benzoic acid, using mole percentage relative to diaminoresorcinol 3 sintered at 350°C for 1245 minutes 4 under vacuum 5 annealed at 340°C for 960 minutes after molding Example 5- Granular compositions containing a block copolymer of 5 percent rigid rod cis- -polybenzoxazole and 95 percent aliphatic polybenzoxazole, and molded articles made from them A functionally terminated rigid rod cis- -polybenzoxazole block is prepared which has an inherent viscosity of 5.77 dL/g, is predominantly terminated at each end by an o-amino-hydroxy moiety, and consists essentially (except for the end groups) of mer units represented by the Formula: The functionally terminated block is reacted in a mixture of methanesulfonic acid and polyphosphoric acid with 4,6-diaminoresorcinol dihydrochloride and sebacic acid. The concentration of solids in the reaction mixture is sufficient to provide a dope containing about 2 weight percent solids, and the ratio of monomers to functionally terminated block is suitable to provide a block copolymer containing about 5 weight percent rigid rod block and about 95 weight percent aliphatic polybenzoxazole block. No terminator is added. The resulting dope is frozen at liquid nitrogen temperature and ground for two hours using 7.4 lbs. of ceramic balls. The frozen granular composition is coagulated in a blender in phosphate buffered slurry with crushed ice while periodically adding aqueous sodium hydroxide as needed to maintain the pH of the system at about 7 to 8. The precipitated granular composition is filtered, washed twice in deionized water and once in acetone for several hours each washing, and dried under air and in a vacuum oven to constant weight, A quantity of powder as shown in Table 1 is pressed under about 20,000 pressure at room temperature for about 10 seconds to form a briquette. Each briquette is molded at the temperature and pressure shown in Table 1 for the time shown in Table 1 to form a disk having a thickness of about 1/-|6-inch (0.16 cm) and a diameter of about 2j-inches (6.4 cm). Each disk is tested for flexural strength and modulus by the test described in ASTM D-790. It has the strength, modulus and strain shown in Table 5. Table 5 - 1 ksi = 1000 psi Example 6- Granular compositions containing a block copolymer of 5 percent rigid rod cis- -polybenzoxazole and 95 percent aliphatic polybenzoxazole, and molded articles made from them A functionally terminated rigid rod cis- polybenzoxazole block is prepared which has an inherent viscosity of 5.1 dL/g, is predominantly terminated at each end by an o-amino-hydroxy moiety, and consists essentially (except for the end groups) of mer units represented by the Formula: 0 The functionally terminated block is reacted in polyphosphoric acid with 4,6-diaminoresorcinol dihydrochloride and sebacic acid. The concentration of ' - solids in the reaction mixture is sufficient to provide a dope containing about 3 weight percent solids, and the ratio of monomers to functionally terminated block is suitable to provide a block copolymer containing about 5 weight percent rigid rod block and about 95 weight percent aliphatic polybenzoxazole block. 2-aminophenol is added as a terminator in a quantity equal to 5 weight percent of the diaminoresorcinol that is reacted with sebacic acid. The resulting polymer has an intrinsic 5 viscosity of 7.93 dL/g. The resulting dope is coagulated in a blender in phosphate buffered aqueous coagulation bath while periodically adding aqueous sodium hydroxide as needed to maintain the pH of the system at about 7 to 8. The 0 precipitated granular composition is filtered, washed several times in deionized water, filtered, and dried in air and in a vacuum oven to constant weight. A 7.3 g quantity of powder is pressed under about 20,000 pressure at room temperature for about 10 seconds to form a briquette. The briquette is molded at 225°C and 20,000 psi pressure for 3 minutes to form a disk having a thickness of about 1/i ~inch (0.16 cm) and a diameter of about 2£-inches (6.4 cm). Each disk is tested for flexural strength and modulus by the test described in ASTM D-790. It has a flexural strength of 4,705 psi and a flexural modulus of 371,000 psi.

Claims: Claims : 1. A block copolymer having (a) rigid rod or semi-rigid polybenzazole polymer blocks and (b) thermoplastic polymer blocks, characterized in that (1) each polybenzazole polymer block contains on average at least 5 mer units and less than 10 mer units; and (2) the block copolymer is thermoplastic and can be compression molded without substantial phase separation. 2. A block copolymer having (1) rigid rod or semi-rigid polybenzazole polymer blocks that contain on average at least 5 mer units per block and (2) thermoplastic polymer blocks of suitable size and proportions so that the block copolymer is flowable at a temperature below its decomposition temperature, characterized in that the block copolymer is in a solid granular form that has an average particle diameter of no more than 1000 μ. 3. A briquette that contains a granular 0 composition of as described in Claim 2. 4. A process for forming a shaped article comprising the step of molding a solid granular ~- composition in a mold at a temperature at which the granular composition is flowable and at a pressure sufficient to cause the granular composition to consolidate and conform to the shape of the mold, characterized in that (1) the granular composition contains a non-phase-separated block copolymer having c (a) rigid or semirigid polybenzazole polymer blocks that contain on average at least 5 mer units per block and (b) thermoplastic polymer blocks of suitable size and proportions so that the block copolymer is flowable at a temperature below its decomposition temperature; and (2) 10 the granular composition has an average particle diameter of no more than 1000 μ. 5. A molded article made by the process as described in Claim 4. 15 6. The invention as described in any one of preceding Claims wherein all polybenzazole polymers in the block copolymer are polybenzoxazole or ~ polybenzothiazole polymers. 7. The invention as described in any one of the preceding Claims wherein the rigid or semirigid polybenzazole block consists of mer units that are 5 represented by any of the Formulae: 0 8. The invention as described in any one of the preceding Claims wherein the thermoplastic block is a thermoplastic polybenzazole polymer that contains mer units represented by any one of the Formulae: 18 wherein : X is a bond or a first divalent linking moiety; 0 each Ar, Ar1 and Ar 3 is an aromatic group; L is a non-linear group that is stable under conditions at which the polymer is synthesized, fabricated and used; R' is an aliphatic group that contains at least '5 about 3 carbon atoms; and each Z is an oxygen atom or a sulfur atom. 9. The invention as described in Claim 8 wherein: 0 L contains two aromatic groups linked by a second divalent linking moiety (X'); X and X" are each a carbonyl group, a sulfonyl 5 group, and oxygen atom or a sulfur atom; and R 1 is an alkyl group or halogenated alkyl group that contains no more than about 12 carbon atoms. 10. The invention as described in any one of 0 Claims 1-7 wherein the the thermoplastic polymer block contains any one of the following polymers: polyamide, thermoplastic polyimide, polyquinoxaline, polyquinoline, poly(aromatic ether ketone) and/or a poly(aromatic ether sulfone), or a copolymer of those polymers with each other and/or polybenzazole. 11. The invention as described in Claim 10 wherein the the thermoplastic polymer block contains a thermoplastic polyamide, poly(aromatic ether) or copolymer of poly(aromatic ether) and polybenzazole.

Inventors: DIXIT THUAN PHUNG, HARRIS WILLIAM JAMES, HWANG WEN-FANG, RASPOR OTTO CARL, DIXIT, THUAN, PHUNG, HARRIS, WILLIAM, JAMES, HWANG, WEN-FANG, RASPOR, OTTO, CARL
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1991
Main classification: C08L77
IPC codes: B29C43, B29K79, C08G73, C08G81, C08J3, C08J5, H05K1