Synthesis and characterization of fluorine-containing cholesteric liquid crystalline polysiloxanes bearing trifluoromethyl-substituted mesogens

• Published in: Liquid crystals 2015-03, Vol.42 (3), p.298-308
• Main Authors: Tian, Mei, Sun, Huan Huan, Tian, Xiao Wei, Xu, Zhi Xin, Wang, Feng Qiao, Yao, Dan Shu, Hu, Jian She
• Format: Article
• Language: English
• Subjects: Chemical synthesis; chiral nematic phase; cholesteryl containing polymer; Differential scanning calorimetry; Diffractometers; fluoro-polymers; Liquid crystal polymers; liquid crystalline polymer (LCP); Liquid crystals; Mesophase; Monomers; Phase transitions; Polymers; Polysiloxanes; smectic phase; Temperature effects; Thermodynamics; Thermogravimetric analysis; Weight loss
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/02678292.2014.986230

A series of side-chain liquid crystal (LC) polysiloxanes were synthesised with Poly(methylhydrogeno)siloxane, 4ʹ-(undec-10-enoyloxy) biphenyl - 4 - yl 4- (trifluoromethyl) benzoate (M th ) and a chiral nematic (N*) LC monomer 1-allyl 10-(cholesteryl)-decanedioate (M ch ). The chemical structures and LC properties of the monomers and polymers were characterised by FTIR, 1 H-NMR, differential scanning calorimetry, thermogravimetric analysis, POM and X-ray diffractometer. M ch is monotropic N* LC. The homopolymer derived from monomer M ch is enantiotropic N* LC. Monomer M th is a smectic A liquid crystal. The copolymers derived from M ch and M th are N* LCs. The temperatures at which 5% weight loss occurred are greater than 300°C for all the fluoro-containing polymers, and the residue weights of the samples at 600°C increased slightly as the content of trifluoromethyl mesogens increased in the polymers. The glass transition temperatures of the polymers increased as trifluoromethyl mesogens increased, too. The N*-I phase transition temperatures show a negative deviate from ideal or linear behaviour. The values of the enthalpy changes for the cholesteryl containing polymers are rather low and this is attributed to the biaxiality of cholesteryl moiety which tends to reduce the change in the orientational order at the N*-I transition. Compared to the monomers, the polymers show wider mesophase region.