Design,Synthesis And Properties Of Biphenyl Side Chain Liquid Crystal Polymers

Due to the good anisotropy and processability,polysiloxane liquid crystal polymers can be used fot different application such as adhesives,protective coatings and optoelectronic materials.In this paper,nine liquid crystal monomers,VmOBC(m=1,2,3,4),V1OBEn(n=6,8,10,12),and V1OBEG,were designed and synthesized firstly,then they were grated onto poly[3-mercaptopyl methylsiloxane](PMMS)via thiol-vinyl click reaction for preparing three series of side chain liquid crystals polymers,coded as PMMS-VmOBC,PMMS-V1OBEn,and PMMS-V1OBEG-VmOBC.The specific results are as follows.(1)Monomers V1OBC,V20BC,and V30BC have nematic mesophase occurring only on cooling,while monomer V40BC show enantiotropic smectic mesophases on heating and cooling.And,their melting(T.)and clearing points(Ti)present odd-even changing with the increase of the spacer chains.For polymers PMMS-VmOBC,all of them are smectic liquid crystals snd their glass transition temperature(Tg)and clearing point(Ti)gradually increase with the extension of the spacer chains.Also,the thermal decomposition temperatures(Td)of these four polymers are above 320?.(2)All four monomers V1OBEn show smectic mesophases,and their Tm values give odd-even changing,while the Ti values decrease first and then increased with the increase of the terminal alkyl chains.After graft polymerization,series PMMS-V1OBEn remain smectic mesophases.With the extension of the terminal alkyl chains,the Tg and Ti values of series PMMS-V1OBEn gradually increases,and the Td values are above 340?.(3)Monomer V1OBEG is cholesteric liquid crystal,its Tm and Ti values are 189.37? and 277.99?,respectively.After graft polymerization,polymer PMMS-V1OBEG is cholesteric mesophase texture on heating,while there is no liquid crystal mesophase on cooling.However,because of the introduction of monomers VmOBC,polymers PMMS-V1OBEG-VmOBC turn into smectic mesophase.In addition,their Td values are all above 280? and give odd-even changing with the increase of the spacer chains of VmOBC(based on the decomposition temperature of 5%).(4)The emissivity values of series PMMS-V1OBEn show a downward trend in phase transition interval,while series PMMS-VmOBC have not such phenomenon,which specific reasons need further study.