Direct polymerization of aromatic diacid dimethyl esters with aromatic diamines II. Control of copolyimide chemical structure

Abstract

Control of the chemical structure of copolyimides through the sequence control of copolyamic acid methyl esters was tried. The copolyamic acid methyl esters were directly synthesized from 2,5-dicarbomethoxy terephthalic acid (p-PMDE) and two diamines, 4,4′-oxydianiline (ODA) and 2,2′-bis (trifluoromethyl) benzidine (PFMB), using phenyl phosphonic dichloride. The average sequence length of the copolyamic acid methyl esters was controlled by the stoichiometric unbalance and monitored by the proton nuclear magnetic resonance spectroscopy (1H NMR). The inherent viscosity of the chemical structure-controlled copolyamic acid methyl ester was 0.39–0.53dl/g. The average sequence length for the random copolymer was ca. 3 and that for the alternating copolymer was greater than 1. Control of the average sequence length became more difficult as the stoichiometric unbalance between the p-PMDE and the diamines increased. The maximum imidization temperatures of the ODA/p-PMDE and PFMB/p-PMDE polyamic acid methyl esters were around 237 and 252°C, respectively. Those of the copolyamic acid methyl esters were between these two temperatures. The maximum imidization temperature of the copolymer approached that of the PFMB/p-PMDE polyamic acid methyl ester as the average sequence length increased.