Phase transitions in a novel combined side-chain/main-chain liquid crystal polyester

摘要

A series of "combined" liquid crystalline polyesters has been synthesized based on the polycondensation of 2,2'0-bis(trifluoromethyl)-4,4'-biphenyldicarbonyl chloride with 2,2'-bis{#omega#-[4-(4-cyanophenyl)phenyoxy]-n-alkoxycarbonyl]}-4,4'-biphenyldiol (PEFBP). In this report, we focus on the phase structure and transition behavior of PEFBP(n =9). In PEFBP(n=9) containing nine methylene units in the side chains, three different ordered phases have been identified by DSC and WAXD experiments in addition to the isotropic melt (I). They are as follows: an orthorhombic crystalline (K_o) phase, a triclinic crystalline (K_T) phase in the high temperature region and a nematic (N) phase. In PEFBP(n = 9), the N and K_O phases are similar to those in the case of PEFBP(n = 11). However, this polymer only presents one triclinic crystalline K_T phase (1). This triclinic phase is the cause of that the K_O phase becomes metastable. The general phase transition sequence is T_g->K_O<->N<->K_T<->N<->I.