Highly soluble polyimides from sterically hindered diamines

Polyimides with enhanced solubility have been synthesized from various arom atic tetracarboxylic dianhydrides and sterically hindered diamines. Intrins ic viscosities in 1-methyl-2-pyrrolidinone (NMP) ranged from 0.28 to 1.05 d L/g. Most of the polyimides were soluble in common solvents such as N,N-dim ethylacetamide, NMP, chloroform and tetrahydrofuran. Polyimides derived fro m thianthrene-2,3,7,8-tetracarboxylic dianhydride (TDAN) and diamino mesity lene (DAM) or diethyltoluene diamine (DETDA) were insoluble in all solvents indicating that polyimide solubility decreased as anhydride rigidity incre ased. Glass transition temperatures ranged from 252 to 398 degrees C and ab ove with the polymers showing little or no weight loss by TGA up to 400 deg rees C in both air and nitrogen. The glass transition temperatures of the p olyimides increased 15 to 98 degrees C (compared to unhindered polyimide an alogs) when one or more methyl group was placed ortho to the imide nitrogen , hindering backbone rotation, chain packing and flexibility. Tough, transp arent films of the soluble polyimides were cast from solution. (C) 1999 Els evier Science Ltd. All rights reserved.