Low molecular weight poly(imide‐amide)s obtained by copolycondensation of 4,4′‐methylenedi(phenyl isocyanate), trimellitic anhydride and benzoic acid in N ‐methyl‐2‐pyrrolidone, 3. Absolute number‐average molecular weights and glass transition temperatures

In depth study of low molecular weight poly(imide‐amide)s (PIA) obtained by copolycondensation of 4,4′‐methylenedi(phenyl isocyanate), trimellitic anhydride and benzoic acid by 1 H and 13 C NMR spectroscopy and size‐exclusion chromatography allows the determination of their absolute number‐average molecular weights M̄ n, abs . Viscosimetric measurements reveal that, dissolved in N ‐methyl‐2‐pyrrolidone, these low molecular weight PIAs should be semi‐rigid because of the presence of very short crystalline chains. By using the semi‐empirical Fox‐Flory relation, the extrapolated glass transition temperature equals 300°C for high molecular weight.