Synthesis of polyamide-imide by blocked-methylene diisocyanates

Abstract

The synthesis of polyamide-imide (PAI) can be performed by the reaction of p-chlorophenol-(PCP) blocked 4,4′-diphenyl methane diisocyanates (BMDI) with trimellitic anhydride (TMA) using a two-stage heating. At 80°C the polyimide oligomers were first formed and the high molecular weight PAI can not be available until the temperature was increased to 120°C and stayed for 3 h, during which the amide groups were formed and the molecular weight was increased. The molecular weights of the synthesized PAIs on various conditions were analyzed by measuring the intrinsic viscosity, amide/imide ratio from IR spectra, and average chain length from GPC. The best reaction conditions for obtaining a high molecular weight PAI by the solution polymerization are: (a) using N-methyl pyrollidone (NMP) as solvent, (b) adding more BMDI/TMA ratio, and (c) adding tert-n-butyl amine as the catalyst for the dissociation of blocked MDI and controlling the catalyst concentration at 0.162M. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1711–1717, 1997