Synthesis and properties of aromatic polyimides containing oxyalkylene linkages

Abstract

A series of para-catenated aromatic diamines containing oxyalkylene linkages, i.e., i.2-bis(4-aminophenoxy)ethane, bis[2-(4-aminnophenoxy)ethyl]ether, 1,2-bis[24{4-aminio-phenoxy)ethoxyjethane and bis{2-[2A4-aminophenoxy)ethoxy]ethyllether were polymerized with 3,3',4.4'benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride. The poly(amic acid)s obtained were imidized by both chemical and thermal methods. It was postulated that the incorporation of the flexible linkages in the polyimides' backbones would result in solubility in organic solvents and moderate glass transition temperatures (T_g) that would allow the polymers to be melt processed. However, the polyimides were insoluble and highly crystalline with melting points (T_m) above 400"C. In an attempt to disrupt the polymers' symmetry. mixtures of the diamines and 1,3-bis(3-aminophenoxy)benzene were polymerized with BTDA. The resulting copolymers were insoluble and semrnicrystalline with T_m values near 310C. A polyimide with similar properties was obtained by polymerizing a disubstituted diamine, 2,2-diethyl-t,3-bis(4-aminophenoxy)propane, with BTDA. A soluble polymer that could be melt processed was prepared from BTDA and a meta-catenated diamine containing an oxyalkylene linkage, bis[2-(3-aminophenoxy)ethyl)ether. The polymer had a strong T_g near 156 'C and a weak T_m near 240C.