Insight into the liquid crystalline behavior of poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene}: a typical thermotropic mesogen-jacketed liquid crystalline polymer

Abstract

Based on the thermodynamic and kinetic analyses, the thermotropic hexagonal columnar liquid crystalline (LC) phase of poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} (PBPCS) at high temperature is self-assembled by driving forces of the conformation entropy and macromolecular interaction, respectively. Because of the strong “coupling effect” between flexible backbone and rigid side chain, the molecular structure of PBPCS can be regarded as “dual chains” model that a flexible backbone and a rigid side chain are in parallel, the backbone and side chain are corresponded to different molecular thermal motion characteristics. When the orientation requirements of the side mesogenic chain are dominant, LC phase appears; when the random motions of flexible backbone are dominant, LC phase disappears. PBPCS demonstrates various types of metastable phases in the LC phase transition. Above LC phase transition temperature, molecular motion of rigid side chain is dominant; therefore, LC phase is formed. In the temperature range from glass transition to LC phase transition, molecular motion of flexible backbone is dominant; therefore, metastable LC phase may be relaxed partly and even disappear. The stability of LC phase can be determined by the kinetic factors, it is related to the residence time for LC phase formation and the interaction among the aggregated columnar macromolecular chains. Metastable LC phase disappeared in the subsequent cooling procedure, however, the stable LC phase was not.