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.