Thermotropic liquid crystal polymers in low molecular weight mesogenic solvents

Thermotropic Liquid Crystal Polymers in Low Molecular Weight Mesogenic Solvents (February 1986) Eric R. George, B.S. (Honors) University of Southern Mississippi M.S., Ph. D. , University of Massachusetts Directed by: Professor Roger S. Porter The crystal to nematic phase transition in Thermotropic Liquid Crystal Polymers (TLCP) was studied. The first application of the Flory-Huggins theory for transition point depression of the crystal to nematic phase transition in TLCP upon the addition of low molecular weight mesogenic solvents was demonstrated. From the extrapolated transition point depression data, the heat of transition (AH u ) was calculated for two TLCP containing random and blocky sequence distributions. The entropy of fusion was calculated from AH u and the order changes at the crystal-nematic transition were characterized for two structurally different liquid crystal copolyesters . The criteria for eutectic versus isomorphous binary phase diagrams were presented and supported by example phase diagrams. Eutectic phase diagrams exhibit separate crystal phases in the solid state while isomorphic phase diagrams result when solid solubility or cocrystallization occurs. The application of the Flory-Huggins theory requires eutectic-type behavior. A new calorimetry technique was discovered from the study of the isomorphic phase diagram of a TLCP containing a main chain azoxy group in para-azoxyanisole. The new technique indicates that TLCP have a higher degree of order than low molecular weight homologs near the nematicisotropic phase transition. Information was provided without knowledge of the transition heat for a theoretical perfect crystal of the TLCP. A new processing technique utilizing the transition point depression of eutectic-type phase diagrams was demonstrated. The technique featured a lower melting, lower viscosity physical blend for melt processing followed by the solid-state transesterification of the low molecular weight liquid crystal (LMWLC) into the polymer backbone. A new class of reactable LMWLC was invented and characterized for the new processing technique.