Synthesis and evaluation of properties of novel aromatic poly(ether-imide) with benzazole pendent groups and flexible ether linkages

Abstract

Three types of new bis(ether-amine) monomers such as 5-(2-benzimidazole)-1,3-bis(4-aminophenoxy)benzene (3), 5-(2-benzoxazole)-1,3-bis(4-aminophenoxy)benzene (4), and 5-(2-benzothiazole)-1,3-bis(4-aminophenoxy)benzene (5) were prepared in three steps, starting from the reaction of 3,5-dihydroxybenzioc acid with 4-fluronitrobenzene in N,N-dimethylformamide (DMF) solution in the presence of potassium carbonate, followed by catalytic reduction of the intermediate dinitro-carboxylic acids, and subsequent condensation of the resulting diamino-carboxylic acids and 1,2-phenylenediamine, 2-aminophenol or 2-aminothiophenol in polyphosphoric acid (PPA), respectively. Three series of modified poly(ether-imide)s (PEIs) bearing pendent benzimidazole, benzoxazole or benzothiazole groups were prepared from the bis(ether-amine)s with dianhydrides by a conventional two-stage process that included ring-opening polycondensation forming the poly(amic acid)s (PAA) and further thermal or chemical imidization forming poly(ether-imide)s. For comparative purposes, reference poly(ether-imide)s were also prepared by reacting bis(ether-amine) lacking pendent groups namely 1,3-bis(4-aminophenoxy)benzene (6) with the same dianhydrides under similar conditions. The modified polymers were obtained in quantitative yields with inherent viscosities between 0.52 and 0.83 dL g⁻¹. Experimental results indicated that all the PEIs had glass transition temperature between 221 and 283 °C, the decomposition temperature at 10% weight loss between 480 and 572 °C under nitrogen.