Physico-chemical studies of polyamides III : isomorphism in copolyamides of long chain units containing oxa- and thia-alkylene linkages

Abstract

Various copolyamides of long repeating chain units were prepared from p-xylylenediamine (PXD) with aliphatic dicarboxylic acids of three structural type ; a, w-alkanedioic, a, w-oxaalkanedioic, and a, w-thiaalkanedioic acids. These copolyamides having the same number of chain atoms with the diamine afforded highly crystalline copolyamides. In the cases of all these copolymers, the plots of the melting points and the densities versus the compositions arc expressed by linear relations. From X-ray examination it is ascertained that the lattice spacing of each copolyamide are unchanged by the composition. These results show that methylene, ether, and thioether linkages are in the relation of isomorphous replacement for each other in these copolyamide systems. Moreover, the linear relationship between the melting point and the composition is explained by assuming that the entropy of fusion in these copolyamides changes linearly according to the change of the composition.