Synthesis and Thermal Properties of Ferroelectric Side Chain Liquid Crystalline Polysiloxanes Based on the Phenyl Ester Mesogen and Oligo(oxyethylene) Spacers. 1. Phenyl Benzoate and Biphenyl Benzoate Mesogenic Groups

Abstract

Four series of ferroelectric side chain polysiloxanes containing oligo(oxyethylene) spacers and (2S)-2-methyl-1-butyl 4-(((4-hydroxyphenyl)carbonyl)oxy)benzoate, (2S)2-methyl-1-butyi 4'-(((4-hydroxyphenyl)carbonyl)oxy)-1,1'-biphenyl-4-carboxylate, (2R)-1-methylheptyl 4'-(((4-hydroxyphenyl)-carbonyl)oxy)-1,1'-biphenyl-4-carboxylate, and 4-[(2S,3s)-(2-chloro-3-methylpentanoyl)oxyl]-1,1'-biphenyl-4'-yl benzoate mesogenic groups were synthesized. The mesomorphic behavior of the four series of ferroelectric side chain liquid crystalline polysiloxanes are studied in this work using DSC, optical polarizing microscopy, and high-resolution X-ray diffraction measurements. Some of these side chain polysiloxanes containing three phenyl rings of ester cores (i.e., -Ph-COO-Ph-Ph-) and a chiral butyl tail present a rich mesomorphic behavior : a blue phase (BP), a cholesteric phase (N * ), a smectic A (S A ) phase, a twist grain boundary A (TGB A ) phase, a chiral smectic F (S F * ) phase, and a chiral smectic C (Sc * ) phase over a wide temperature range (around 160 °C). Another series containing three phenyl rings of ester cores and a chiral heptyl chain tail only reveal the S A phase and TGB A phase. The intermediary twist grain boundary phase would display an iridescent Grandjean plane or a filament texture. Results obtained in this study seem to imply that the tendency toward chiral smectic C mesomorphism increases as the rigidity of phenyl ester mesogens increases via the flexible oligo-(oxyethylene) spacer system, and the thermal stability of the chiral smectic C mesophase is determined by the flexibility of the chiral tail.