MISCIBILITY OF POLYAMIDE BLENDS .1. MOLECULAR MODELING OF POLY(NORMAL-METHYLENEISOPHTHALAMIDE) POLY(META-PHENYLENEISOPHTHALAMIDE) BLENDS

The miscibility of blends of two polyamides, poly(n-methyleneisophthalamide), or nI nylons, for n = 3-9 and poly(m-phenyleneisophthalamide), or mpI, has been investigated by using differential scanning calorimetry. For the polymers studied, only the blends with n = 6 and n = 7 were found completely miscible at all concentrations. Partial miscibility was observed for the 8I nylon/mpI and the 9I nylon/mpI blends. The results are confronted to current predictive methods, and possible causes for the discrepancy between predicted and observed behavior are discussed. A correlation between miscibility and the number of atoms forming hydrogen bonds per the number of non-hydrogen atoms in the repeat unit of the polymers has been noted. It is believed to stem from the energy contribution of the hydrogen bonds in the miscible blends and is proposed as a rule of thumb for the miscibility prediction for systems forming strong hydrogen bonds, in particular when the chi parameters are not known. Molecular modeling has been used for the first time to investigate the formation of interchain hydrogen bonds in the blends and is proposed as an aid for the study of miscibility in systems where strong hydrogen bonds occur.