Side-Chain Cholesteric Liquid Crystalline Elastomers Derived from a Mesogenic Cross-Linking Agent

Abstract

The synthesis of the two monomers M 1 and M2 and a series of new side-chain cholesteric liquid crystalline elastomers P2-P8 is presented. The chemical structures of the monomers and elastomers obtained were confirmed by FTIR or 1 H NMR spectroscopy. The cross-link density of the elastomers was determined by swelling experiments. The mesomorphic properties were investigated by differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), polarizing optical microscopy (POM), and X-ray diffraction (XRD) measurements. Monomer M 1 showed a cholesteric phase, and M2 revealed smectic and nematic phases. The effect of the cross-link density on the phase behavior of P2-P8 is discussed. Elastomers P2-P6 containing less than 12 mol % of the cross-linking units displayed elasticity, reversible liquid crystalline phase transition, wide mesophase temperature ranges, and high thermal stability. Elastomer P 7 displayed stress-induced birefringence, and P8 showed only elasticity with no other texture. Experimental results demonstrated that the glass transition temperatures increased, and the isotropization temperatures and the mesophase temperature ranges of P 2-P6 decreased with increasing cross-link density.

Liquid crystalline elastomers based on cyclic cyclosiloxane and mesogenic crosslinking units

“…The unique optical properties of cholesteric LC are related to the helical supermolecular structure of the cholesteric phase. The wavelength, k max , of reflected light from a cholesteric sample is given by [15] k…”

“…Introduction of chiral functional groups to LC polymers has become one of the most important and complex topics in liquid crystal research. Chiral LC polymers may exhibit a marvelous variety of mesophases, including the blue phase, the cholesteric phase, and the chiral smectic C phase [11][12][13][14][15].…”

New thermochromic liquid–crystalline polymer: Synthesis and phase behavior

“…M 1 was prepared according to the similar procedures previously reported by Hu et al 20 M 2 was obtained through undecenyl acid chloride reacted with 5-aminomalachite green lactone in THF in the presence of pyridine. IR spectra of M 2 showed characteristic bands at 1762, 1735, and 1611-1521 cm Ϫ1 attributed to ester CϭO and aromatic CϭC stretching bands.…”

Effect of the length of the carbochain on the phase behavior of side‐chain cholesteric liquid‐crystalline elastomers

“…The cold reaction mixture was precipitated into water, and the precipitated product was isolated by filtration and recrystallized from ethanol (yield ϭ 34%, mp ϭ 96°C, [␣] 589 17.2 ϭ Ϫ75.5°). Specific rotation of M 3 solutions of 8 g/ml in the toluene were measured in 2 ml cuvettes of 100 mm length using light of a Na-lamp at A ϭ 589 nm and at 17 …”

“…[15][16][17] In this study, the synthesis of two new series (PI and PII) of side-chain cholesteric LCEs derived from two nematic LC monomers, ethyloxy-4-allyloxybiphenyl-4Ј-benzoate (M 1 ) and pentyloxy-4-allyloxybiphenyl-4Ј-benzoate (M 2 ), and a chiral crosslinking agent, isosorbide 4-allyloxybenzoyl bisate (M 3 ), was performed. The reason we chose isosorbide as the chiral material is that it possesses a high twisting power, and obviously, a high molar fraction of isosorbide generates helixes with a pitch that is too small (or large) for an interaction with visible light.…”