New rigid-rod and strictly alternating poly(benzoxazole-imide)s containing methyl-substituted p-phenylene units in the main chain

Full Paper: A series of new strictly alternating poly(o-hydroxy amide-imide)s with high molecular weight were synthesized by low-temperature solution polycondensation from the preformed imide ring and methyl- or dimethyl-substituted p-phenylene-containing diacyl chlorides of 2,5-bis(trimellitimido)toluene or 1,4-bis(trimellitimido)-2,5-dimethylbenzene and three bis(o-amino phenol)s. All the poly(o-hydroxy amide-imide)s are readily soluble in a variety of organic solvents such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). Transparent and flexible films of these polymers were cast from NMP solutions. The tensile strength of the films ranges from 90-105 MPa and elongation at break from 7-12%. Subsequent thermal cyclodehydration of the poly(o-hydroxy amide-imide)s afforded novel rigid-rod and strictly alternating poly(benzoxazole-imide)s. They exhibit glass transition temperatures in the range of 316-345 degrees C and are stable up to 500 degrees C in air or nitrogen, with a 10% weight loss temperature in nitrogen ranging from 550-585 degrees C.