CRYSTALLINE POLY(ORGANOPHOSPHAZENE) BLENDS AND COPOLYMERS

The thermal transition behavior of a number of one-to-one aryloxy poly(phosphazene) copolymers with varied para and meta substituted phenoxy repeat units and several related homopolymer blends has been studied. From DSC experiments on the blends, it is concluded that the crystalline phases, and in some cases the amorphous phases as well, are incompatible. All the copolymers are crystalline and exhibit the T(1) transition to a mesomorphic state typical of poly(phosphazene) homopolymers. Based on the thermal transition behavior, the copolymers can be divided into two classes. Class I copolymers, with similar meta or para substituted repeat units, exhibit T(1) transitions close to homopolymer values and enthalpies at least 75% of theoretical. Class II copolymers, with mixed meta/para substituted phenoxy repeat units, exhibit T(1) values lower than either homopolymer and enthalpies less than one-halt the rule-of-mixtures value. The crystalline behavior is attributed to isomorphism. X-ray results on the p-chlorophenoxy/p-cresoxypoly-(phosphazene), a class I copolymer, show that only a single unit cell occurs, while in a typical class II copolymer two unit cells are present. This suggests that class I copolymers exhibit type I and class II type II isomorphism in the sense defined by Natta and by Wunderlich. © 1979, American Chemical Society. All rights reserved.