Tolylene Diisocyanate-Based Poly(imido-amide)s, 1. Microstructure and Distributions of Amide and Imide Groups studied by1H and13C NMR

Thermostable tolylene diisocyanate (D)-based poly(imide-amide)s (PIA) are obtained by homogeneous polycondensation at completion between D (a mixture of two isomers) and trimellic anhydride (T) in N,N′-dimethylene urea solvent at 185°C. The study of the microstructures of these PIAs by 1H and quantitative 13C NMR is efficiently aided by using (D + phthalic anhydride) and (D + benzoic acid) model condensates. In all cases, imide (I) groups are found to be slightly in deficit and traces of in-chain amic acid groups (precursors of I) are present. With tolylene 2,4-diisocyanate (D′), A (amide) and I groups are preferably formed at the ortho (or 2) and at the para (or 4) positions relative to the methyl group of the tolylene cycle respectively. The concentration of A2I4 sequences are found to equal two times that of I2A4. For tolylene 2,6-diisocyanate (D″), the concentration of A2I6 mixed sequence amounts to three times that of A2A6 or I2I6. The variations of the concentrations of AiAj, AiIj, IiIj sequences versus the composition of D (= x D′ + y D′′, x + y = 1) are perfectly linear. I being bulkier than A, the formations of I and A groups on tolylene cycles are found to be mainly governed by steric hindrance effects.