Synthesis and characterization of heterocyclic ring-containing high temperature polymers

Abstract

Two heterocyclic ring-containing diamine monomers were synthesized. One is 6,4``-diamino-2-phenylbenzimidazole (BIA, 3) and the other is 1,3-di-p-aminophenyl-4-cyano-5-aminopyrazole (PYA, 13). The monomer with benzimidazole-ring BIA was prepared from 4-nitrobenzoyl chloride and 4-nitro-1,2-phenylenediamine with 3 steps. A series of homopoly(amide imide)s and copoly(amide imide)s were prepared from BIA-ODA-TMAC via one-pot synthetic method. The degree of imidization of soluble PAIs containing benzimidazole-ring can be controlled by monomer composition and solution imidization conditions in one-pot synthetic method. The structure of PAIs was confirmed by IR and $^1H$ NMR spectroscopy. All poly(amide imide)s synthesized by one-pot synthetic method were soluble in polar aprotic solvent, but became insoluble in any organic solvents after thermal curing. The thermal stability of the PAIs increased as the polymers contain more BIA units. The new pyrazole ring-containing monomer with the amino and cyano groups PYA was prepared from 4-nitrobenzoyl chloride and 4-nitrophenyl hydrazine with 4 steps. This monomer was converted to polyamides and polyimides with aromatic diacid chlorides and aromatic dianhydrides, respectively. The amino and cyano groups on the pyrazole-ring were not affected during polymerization. The result of the model reaction with monofunctional acid chloride and anhydride showed that the amino groups on the pyrazole ring was not participated in polymerization. The creasable, transparent, and mechanically strong films were obtained in all cases. The polyamides were soluble in polar aprotic solvents and boiling acetone and THF, but the polyimides were insoluble in any organic solvents. The polyamides have high $T_g$ values and they are stable up to 490℃ in nitrogen. But the polyamides are partially degraded at 300℃ in air due to the amino group on the pyrazole-ring. The polyimides have higher thermal stability than the polyamides. Surprisingly, th...