Synthesis of polyphenylquinoxaline copolymers via aromatic nucleophilic substitution reactions of an A-B quinoxaline monomer

A self-polymerizable quinoxaline monomer (A-B) has been synthesized and pol ymerized via aromatic nucleophilic substitution reactions. An isomeric mixt ure of self-polymerizable quinoxaline monomers-2-(4-hydroxyphenyl)-3-phenyl -6-fluoroquinoxaline and 3-(4-hydroxyphenyl)-2-phenyl-6-fluoroquin polymeri zed in N-methyl-2-pyrrolidinone (NMP) to afford high molecular weight polyp henylquinoxaline (PPQ) with intrinsic viscosities up to 1.91 dL/g and a gla ss-transition temperature (T-g) of 251 degreesC. A series of comonomers was polymerized with A-B to form PPQ/polysulfone (PS), PPQ/polyetherether keto ne (PEEK), and PPQ/polyethersulfone (PES) copolymers. The copolymers readil y obtained high intrinsic viscosities when fluorine was displaced in NMP un der reflux. However, single-electron transfer (SET) side reactions, which l imit molecular weight, played a more dominant role when chlorine was displa ced instead of fluorine. SET side reactions were minimized in the synthesis of PPQ/PS copolymers through mild polymerization conditions in NMP for lon ger polymerization times. Thus, the T-g's of PES (T-g = 220 degreesC), PEEK (T-g = 145 degreesC), and PS (T-g = 195 degreesC) were raised through the incorporation of quinoxaline units into the polymer. Copolymers with high i ntrinsic viscosities resulted in all cases, except in the case Df PPQ/PEEK copolymers when 4,4 ' -dichlorobenzophenone was the comonomer. (C) 2001 Joh n Wiley & Sons, Inc.