Synthesis of linear and dendritic high temperature polymers containing curable enaminonitrile groups

Abstract

New diamine monomers containing one enaminonitrile unit, [(p-aminophenylamino)-4-aminophenylmethylidene]propanedinitrile (4) and [(m-amino-phenylamino)-4- aminophenylmethylidene]propanedinitrile (5) were prepared from (chloro-4-nitrophenylmethylidene)propanedinitrile (1) in 2 steps, and polymerized with commercially available aromatic dianhydrides such as pyromellitic dianhydride (PMDA), 3,3’4,4’-biphenyl tetracarboxylic dianhydride (BPDA), 3,3’4,4’-benzophenone tetracarboxylic dianhydride (BTDA), 4,4’-oxyphthalic dianhydride (ODPA), and 4,4’-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), to curable aromatic polyimides. In the case of the polymerization of the para-linked diamine monomer 4 by chemical imidization method or solution imidization method, precipitation occurred during the imidization. However, polymerization of the meta-linked diamine 5 via solution imidization method in NMP proceeded homogeneously and the fully imidized soluble polymers were obtained in quantitative yield. Intrinsic viscosity of these polymers ranged from 0.45 to 0.54 dL/g. The 5% weight loss of the polymers occurred in the range of 524-572℃ in nitrogen, and 493-519℃ in air. All the polymers exhibited broad irreversible exothermic transition between 300 and 450℃ in DSC, indicating curing of enaminonitrile groups, and became insoluble after curing. Also, the diamine monomers 4 and 5 were polymerized with commercially available aromatic diacid chlorides via the low temperature solution polycondensation to new aromatic polyamides containing enaminonitrile groups. The synthesized polyamides, which do not have any flexible linkage, have the structural analogy to Kevlar and Nomex. The polymers showed excellent thermal stability as well as improved solubility compared to Kevlar. They are soluble in polar aprotic solvents such as N-methylpyrrolidone and dimethyl sulfoxide. The 1:1 copolymerization of 4 and para-phenylenediamine produced the copolyamide that has the same struc...