Preparation of polyimide powder

A polyimide powder was prepared from 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA). Polyimide powder having low molecular weight was prepared by imidizing low-molecular-weight polyamic acid. The molecular weight of this polyimide powder increased on heating in a solid state. The molecular weight increased with the decrease of crystallinity of polyimide. © 1996 John Wiley & Sons, Inc.