Thin-film polymerization and Metropolis Monte Carlo simulation of thermotropic liquid crystalline poly(ester-amide)s

Abstract

A series of perfluoroalkyl dicarboxylic acids with different lengths of fluorinated aliphatic segments have been introduced into the 2,6-acetoxynaphthoic acid (ANA) and acetoxy acetanilide (AAA) system and their effects on the evolution of liquid crystal texture and liquid crystallinity have been investigated. The perfluoroalkyl dicarboxylic acids are tetrafluorosuccinic acid (TFSA, n=2), perfluorosuberic acid (PFSUA, n=6) and perfluorosebacic acid (PFSEA, n=8). Novel liquid crystalline polymers (LCPs) made from fluorinated poly(ester-amide)s have been identified; supported by molecular simulation (“RIS” Metropolis Monte Carlo method) and confirmed by the thin film polymerization. Based on computational results, all systems (ANA/AAA/perfluoroalkyl) satisfy the minimum requirement for thermotropic LC formation with persistence ratios larger than 6.42. Moreover, the results obtained also suggest that the chain stiffness and persistence length increase linearly with (CF2)n spacers. The effects of perfluoroalkyl aliphatic spacers on the LC texture evolution, generation and annihilation have been determined by in situ polymerization under a polarizing light microscope. The longest aliphatic perfluoroalkyl spacer (n=8) tends to induce a crystal phase, whereas short aliphatic spacers (n=2 and 6) appear to be more favorable in LC formation. Ternary phase diagrams were plotted to show the relationship among monomer structure, composition, anisotropic and crystalline phases. In addition, Fourier transform infrared spectroscopy (FTIR) results confirm the formation of LCPs, acetoxy group completely disappears after the reaction and ester group forms at the end of the reaction.