METHACRYLATE-BASED SIDE-CHAIN LIQUID CRYSTAL COPOLYMERS CONTAINING BIPHENYL MESOGENS AND CINNAMATE GROUPS

Abstract

Liquid crystal(LC) polymers have been extensively investigated for their unique properties and many potential applications.Introducing cinnamate functional groups into the polymers can combine the mesogenic properties of LC polymers with the photo-crosslinking ability of the photosensitive groups.In this work,a methacrylate-based monomer(M_1) functionalized with mesogenic biphenyl and cinnamate groups was synthesized via nucleophilic substitution and DCC esterification reactions following a newly designed synthetic route.The overall yield was much higher than that reported before.Another methacrylate monomer(M_2) functionalized with mesogenic biphenyl and n-butyl end group was also synthesized in the same way.The homopolymers of the two monomers and a series of new liquid crystalline copolymers have been synthesized by solution radical polymerization with different feed ratios of the two monomers.The structures of the monomers and the polymers were characterized by~1H-NMR and FT-IR.~1H-NMR results revealed that the contents of M_2 in all of the copolymers were higher than the corresponding feed ratios,which indicateded that M_2 was more reactive than M_1.The liquid crystalline(LC) phase behavior was investigated by differential scanning calorimetry(DSC),polarized optical microscopy(POM) and wide angle and small angle X-ray diffraction(WAXD and SAXD).The monomer with cinnamate group as its end(M_1) exhibited no LC behavior while the monomer with n-butyl as end group(M_2) showed smectic LC behavior.The homopolymer of M_1(P_1) and the homopolymer of M_2(P_9) showed weak anisotropy and thermotropic smectic LC phase,respectively.The copolymers(P_2～P_8 with increasing ratio of M_2 to M_1) all showed thermotropic LC behavior.The copolymers P_2～P_5 exhibited characteristic features of nematic LC phases and P_6～P_9 showed smectic phase behavior.With the increase of the content of M_2 in the copolymers,the glass transition temperature,the melting point and the clearing point increased.As the cinnamate functional groups in the LC polymer can be crosslinked through photo-induced cycloaddition reaction,the polymer can be used to prepare LC elastomers.