Thermal behaviour and structure of cyanophenoxy copolymers of poly(bis-phenoxyphosphazene)

The effect of an increasing amount of cyanophenoxy groups on the thermal behaviour and structure of poly(bis-phenoxyphosphazene) was studied by differential scanning calorimetry, X-ray diffraction and thermo-optical analysis. The thermotropic behaviour was preserved in the copolymers, but the crystallinity and the crystal-liquid crystal transition temperatures were considerably lowered as the content in cyano groups increased. Polymorphic forms existed in the copolymer with 6% of cyano groups, as was the case in poly(bis-phenoxyphosphazene). The obtained mesophases had the same structure as that observed in the homopolymer. The kinetics of crystallization from the mesophase were analysed and Avrami exponents of n = 3 and 4 have been found. The temperature at which the mesophase is held prior to crystallization was found to have an important influence on the crystallization process. (C) 1996 Elsevier Science Ltd