THERMOTROPIC BEHAVIOR OF POLY(FLUOROALKOX YPHOSPHAZENE)S - THE EFFECTS DUE TO THE LENGTH OF PENDANT SIDE-CHAINS

A homologous series of poly(fluoroalkoxyorganophosphazene)s with side chains of different lengths was examined using X-ray scattering, diffe rential scanning calorimetry, and dynamic mechanical studies. It was f ound that the first member of the series with a two-carbon-atoms-long side chain may exist in three phase states: low-temperature crystallin e, mesomorphic, and melt. Increasing the length of the side chain by o ne CF2 unit was shown to enhance the effects due to pendant side group s and cause the appearance of another, high-temperature, crystalline p hase state. The effect of the side chains became dominating when the l ength of the side chain was increased by another two CF2 units; as a r esult, the third member of the homologous series (contrary to the firs t two) did not show the low-temperature crystalline phase. Two low-tem perature relaxation transitions were identified. One of these was rela ted to the mobility of the terminal units of the side chains, whereas the other was assigned to the glass transition temperature of polyphos phazenes.