The biphasic behaviour of a thermotropic polymesomorphic polyester I. Time evolution of phase separation

The time evolution of biphase segregation at the nematic-isotropic (N-I) as well as the S-a-N and S-b-S-a transitions of a main chain polyester was studied by annealing the sample inside the relevant biphasic regions. Only the splitting of the N-I transition process is observed when the sample is annealed at a temperature in the N-I biphasic gap. In contrast, when the sample is annealed at a temperature in the biphasic regions involving a smectic phase, both the S-a-N and S-b-S-a processes are split into two components, whereas the N-I transition process is found to be little affected by the thermal treatment. The peak temperature difference between the biphase segregated components and the overall peak resolution indicates that the more efficient segregation occurs for the transition at which the biphasic separation had been performed. The overall phenomenology shows that the molar mass distribution in the two biphase segregated components is: (a) optimized for the specific transition at which the biphasic separation is performed: and (b) different for the various transitions according to their distinct symmetry and steric packing features. (C) 2000 Published by Elsevier Science Ltd.