Synthesis of NLO diacrylate monomers and their photocopolymerizations with LC diacrylate monomers in mixed liquid crystalline state

Abstract

The photocopolymerization (photocrosslinking) of mixed liquid crystals (LCs) consisting of LC diacrylate monomers and nonlinear optical (NLO) diacrylate monomers exhibiting no liquid crystallinity under contact poling at optimum temperature was investigated to obtain a thermally stable NLO polymeric material. Novel NLO monomers, BAASA and BAOSA, as well as LC monomers, BAOOB3 and PAOB, were synthesized and the liquid crystallinity of their mixed LCs was investigated. The affinity of BAOSA with the LC monomers is generally better than that of BAASA. LC mixtures prepared using BAOOB3 as LC matrix show only a smectic phase and do not respond to poling though fixation of the mixture by photocrosslinking occurs tightly. A PAOB matrix results in a nematic phase but not a smectic phase and the LC mixture responds not only to poling but also to photocopolymerization in the nematic phase. The photocrosslinking reaction of a BAOSA/PAOB (mole ratio 1/9) mixture under poling at 129°C (nematic phase) proceeds effectively and gives a thermally stable polymer film with a χ33(2) value of 1.2–1.7 × 10−8 esu1 esu = electrostatic unit; 1 esu = 2.693 × 1014 C3/J2. , while the polymer film formed by photocrosslinking at 140°C (isotropic phase) shows a one order lower χ33(2) value (3–5 × 10−9 esu).