Comparative analysis of the structure of two thermotropic LC copolyesters

A comparative study of the structures of two thermotropic liquid crystal copolyesters (LCP) was carried out. The first copolymer, LCP-1, comprises three different monomer units of equal length, whereas the second copolymer, LCP-2, contains two monomer units which differ significantly in length. Both copolymers exhibit random structure. it was established that despite the irregular structure both copolymers have the ability to crystallize. Moreover, during crystallization of LCP-I microphase separation into two phases occurs. Each phase has an orthorhombic crystal structure but with slightly different parameters of the unit cell. The reason for this difference is probably associated with configuration isomerism because of possible head-to-head or head-to-tail additions during synthesis of the copolyester. Upon annealing, the maximum degrees of crystallinity are 35% and 25% for LCP-1 and LCP-2, respectively. The noncrystalline fraction of the material, whose content exceeds appreciably the content of the crystalline phase, shows a LC smectic structure. However, the fundamental difference between the two copolymers is that, in the case of LCP-1, the periodic layer structure is observed, whereas for LCP-2 the layer structure is aperiodic. The above phenomena are universal, and this makes it possible to predict the structure and character of temperature behavior of any representative of the class of fully aromatic rigid-chain copolyesters only from the chemical formula of the copolymer.