Thermolysis of methylenedianiline (MDA) 1,2,3,6-tetrahydrophthalic (THP) bismides up to 371 degrees C, produces aromatic product, with a concomitant lowering in cross-linking This aromatization is responsible for both the unmoved thermal oxidative stability of THP end-capped polyimides and their substantial frangibility In the hope of inhibiting precuring aromatization, 2,3-dimethyl, 3,3-dimethyl, and,2,3-trimethyl THP analogues were synthesized and reacted with MDA in a 2.1 ratio, heating gradually from 204 to 371 degrees C In the lower temperature range, monoimide transforms to bisimide At temperatures above 320 degrees C. cross-linking predominates generally reaching similar to 30% at 371 degrees C, though it was as much as 69% for 3,3-dimethyl THP The surprising facility of cross-linking in the latter was con elated to the double bond length of the it imide formed via thermal enolization The aromatization (2-25%) observed in these methylated systems at higher temperatures presumably results from oxidative decarboxylation of the pendant methyls, which is the preferred pathway for degradation after cross-linking