Study On The Preparation And Self-assembly Behaviours Of Polysiloxane Side Chain Liquid Crystalline Polymers

Polysiloxane side chain liquid crystalline polymers(PSCLCPs),which combine the anisotropy of lowmolecular mass weight liquid crystals with the mechanical performance of polymers,show wide potential applications as electro-optic materials,adhesive,protective coatings and biocompatibility material.However,for the traditional hydrosilylation method of PSCLCPs preparation,the purification difficulty derived from the usage of expensive noble metal platinum catalysts,the complexity of the chemical structures and performance of the products attributing to the coexistence of Markovnikov and anti-Markovnikov addition reaction have limited their wide applications.The thiol-ene addition reaction,namely hydrothiolation of a C=C bond,as a representative click reaction with features of high efficiency,strong stereo-selectivity,simple reaction conditions with the products of anti-Markovnikov addition reaction only,has been widely investigated.Additionally,some illegal behaviours in today's rapidly developing society,such as copy or replication without the permission of the copyright person and for the purpose of cheating,have caused significant interference and economic loss for the state,corporations,groups and individuals.So it is particularly important to take a simply,easily,and highly effective measures to prevent those illegal practices.Liquid crystals,which can quickly respond to the external stimulations,such as electricity,light,heat,magnetism and so on,is recognized as one of the most competitive anti-counterfeiting materials in the next generation.In this article,focus on the advantages of thiol-ene click reaction and the usage of liquid crystalline materials in the field of anti-fake,we designed and prepared two series of liquid crystalling polymers based on the poly[3-mercaptopropylmethylsiloxane](PMMS)backbone,and a series of linear siloxane tetramers based on the polymethylhydrosiloxane(PMHS)main chain.The effect and evolution law of some variables,such as molecular structure of mesogenic unit,molar ratio changes between the different mesogenic unit,the terminal polar group of side chain and molecular structure of backbone,on the self-assembly behaviours and condensed structures of the obtained liquid crystalline polymers have been systematically investigated.The main research contents are as follows:(1)A battery of thermotropic polysiloxane side chain liquid crystalline polymers with different molar contents of chiral cholesteryl-4-(allyloxy)benzoate(M1)and achiral 4-methoxyphenyl 4-(allyloxy)benzoate(M2),denoted as PMMS-M2-X(X= 0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.85,0.9,and 1.0,respectively,the molar ratio of the achiral unit(XM2)in a specific polymer),was successfully designed and synthesized via thiol-ene click chemistry.The self-assembly behaviours and condensed structures of these polymers greatly depended on the molar ratio of chiral and achiral side chains.Moreover,when the molar ratio of the chiral group or achiral group was about 0.1,a microphase-separated smectic morphology could be found,indicating that the introduction of a small amount of any components in the copolymers might destroy the well-ordered structures.(2)A series of thermotropic polysiloxane side chain liquid crystal polymers with different molar contents of chiral cholesteryl-4-(allyloxy)benzoate(M1)and achiral 4-Cyanophenyl 4-(Allyloxy)Benzoate(M3),denoted as PMMS-M3-X(X= 0,0.2,0.4,0.6,0.8,and 1.0,respectively,the molar ratio of the achiral unit(XM3)in a specific polymer),was successfully designed and synthesized via thiol-ene click chemistry.Different from PMMS-M2-X polymers with methoxy-terminated achiral side chains mentioned above,attributing to the decisive role of the polarity interaction,all the polymers only developed a monolayer interdigitated SmA phase in which the period arrangement was determined by the cyano-terminated side chains,the increased content of cholesterol-terminated chiral side chains just expanded the distance between neighboring molecules within a layer.(3)A series of new linear polysiloxane tetramers-with different molar contents of chiral cholesteryl-4-(allyloxy)benzoate(M1)and methoxy-terminated achiral 4-methoxyphenyl 4-(allyloxy)benzoate(M2)was successfully synthesized via a typical hydrosilylation reaction.The self-assembly behaviours and condensed structures of these polymers also greatly depended on the molar ratio of chiral and achiral side chains.Compard with the cyclic siloxane tetramers which have the same side chains and polymerization degree,the absence of blue phase(BP)in the linear polysiloxane tetramers with high concertration of chiral side chains indicated that the existence of ring tension played one of the key factors on the formation of blue phase.Compared with polymers PMMS-M2-X which have higher polymerization degree and longer spacer,the disappearence of high ordered SmE phase suggested that a longer backbone and spacer were more benicial to stabilize the higher ordered LC phase.Additionally,an unusual phenomenon of the centre selective light reflection wavelength near cholesteric-isotropic transition for polymers with cholesteric phase,which decreased dramatically(blue shift)at first,then had a remarkable red shift with increasing molar ratio of M1,was first observed.(4)Combined with quantum dots(QDs),the first-tier,the second-tier,and the third-tier anti-counterfeiting performances of liquid crystalline polymers,which was used as anti-counterfeiting materials,were perliminary explored.A composite film with multiple anti-counterfeiting features was obtained by superposing the CdSe/ZnS QDs/acrylate polymer photoluminescence film(QDs Matrix)and the PS4-M1B-0.30/R811 composite cholesteric film(CLCFs)together,where the QDs Matrix was placed at the bottom while the CLCFs was at the top.The anti-counterfeit effect of this composite film was implemented as follows.The first-tier anti-counterfeiting effect was successfully realized by using the obvious phenomeno of optically variable and thermochomic of cholesteric phase.Utilizing circularly polarized discoloration of cholesteric phase,second-line anti-counterfeiting effect was feasibly realized.By using the changes of the fluorescence emission spectrum or the different fluorescence pattern,which were as a result of the different raltive positions between the center selective reflection wavelength of CLCFs and the photoluminescence peak of QDs Matrix at different temperatures,the third-tier anti-counterfeiting effect could be achieved.