Synthesis and Characterization of Polyimides Based on 3,6-Diphenylpyromellitic Dianhydride

3,6-Diphenylpyromellitic dianhydride (DPPMDA) has been synthesized from 2,5-diphenyl-3,4-bis(4-methoxyphenyl)cyclopentadiene-1-one and dimethyl acetylenedicarboxylate. The monomer was polymerized with 11 aromatic diamines in refluxing m-cresol containing isoquinoline to afford two new series of phenylated polyimides. The polymers containing flexible ether or methylene linkages, meta-catenation, or cardo linkages were soluble in m-cresol, N-methylpyrrolidinone, and symtetrachloroethane. Their intrinsic viscosities ranged from 0.81 to 2.40 dl/g. The polymers prepared from 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, and 1,3-diaminobenzene underwent extensive crystallization in concentrated m-cresol solutions. These polymers displayed weak glass-transition temperatures between 310°C and 320°C and melting points near 430°C. Three para-catenated, rigid-rod polymers were also prepared from DPPMDA and substituted 4,4′-diaminobiphenyls that displayed limited solubility in m-cresol. Solutions containing 8.5 to 15% (w/v) of the polymer prepared from 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl underwent reversible gellation near 85°C. Liquid-crystalline spherulites formed in the gels upon standing at ambient temperatures.