Multi-Methyl-Substituted Polyphenylquinoxalines with High Solubility and High Glass Transition Temperatures: Synthesis and Characterization

New polyphenylquinoxalines (PPQs) containing methyl substituents have been synthesized and characterized. The PPQs were prepared by the polycondensation of a newly-developed aromatic tetraketone, 4,4' -bis(4-benzilyloxy)-3,3',5,5' -tetramethylbiphenyl (III) and aromatic tetraamines. Compared with the non-methyl-substituted PPQs derived from 1,4-bis (4-benzilyloxy)benzene (I) and 4,4' -bis(4-benzilyloxy)biphenyl (II), the obtained polymers exhibited better solubility. They were soluble not only in the common m-cresol and chloroform, but in polar aprotic solvent N-methyl-2-pyrrolidinone (NMP). The polymers showed glass transition temperatures of 325 degrees C for PPQ-IIIa (from III and 3,3',4,4' -tetraaminobiphenyl) and 287 degrees C for PPQ-IIIb (from III and 3,3',4,4' -tetraaminodiphenyl ether), which were much higher than their analogues. The PPQs exhibited good thermal stability up to 470 degrees C in nitrogen and good optical transparency at 450 nm with a thickness of around 10 m. The refractive indices and birefringences of the PPQs were in the range of 1.6998-1.7739 and 0.0002-0.0007, respectively.