Synthesis Of Side-Chain Liquid Crystal Polymers Based On Cholesterol And Study On Their Liquid Crystal Phase Formation Mechanism

Cholesterol Side Chain Liquid Crystalline Polymers?Chol-SCLCPs?are widely used in optoelectronic materials,color information recording,biomedicine and other fields,but their applications depend on the phase behavior and structure of Chol-SCLCPs.Therefore,it is a hot topic to study the relationship between the structure of Chol-SCLCPs molecular chain and the phase structure.Based on literature review,we can know that poly?methacrylic acid?cholesterol esters without flexible spacer possessed smectic phase,and no LC phase structure was discovered in poly?acrylic acid?cholesterol esters.In order to explore the mechanism,Firstly,two series of homopolymers without the spacers,poly?methacrylic acid?cholesterol esters?PCholMC_n?and poly?acrylic acid?cholesterol esters?PCholAC_n?with different molecular weights?M_n?,were achieved by reversible addition-fragmentation chain transfer polymerization.The influence of molecular weight effect on the liquid crystallinity of two kinds of cholesterol side-chain liquid crystalline polymers?Chol-SCLCPs?without flexible spacers has been investigated.Secondly,cholesteryl methacrylate and cholesteryl acrylate were copolymerized with methyl acrylate respectively.The effects of the density of mesogenic units and the flexibility of molecular chains on the liquid crystal properties of these two types of Chol-SCLCPs were studied by changing the ratio of the two monomers.Thirdly,three series of polymers with different flexible spacer lengths were synthesized through molecular design.The effects of the main chain structure and the length of flexible spacer on the self-assembly behavior of Chol-SCLCPs were investigated.The results are as follows:1.Two series of cholesterol side-chain liquid crystalline polymers without flexible spacer,poly?acrylic acid?cholesterol ester?PCholAC_n?and poly?methacrylic acid?cholesterol esters?PCholMCn?with different M_n were synthesized by RAFT polymerization?n denotes the degree of polymerization?.GPC test showed that the M_n of PCholAC_n increased from 3.1×10³ g/mol to 12.7×10³ g/mol,and the M_n of PCholMC_n increased from 3.7×10³ g/mol to 14.5×10³ g/mol.In addition,polydispersion index?PDI?of all polymers was less than 1.1.The phase behavior and phase structure of PCholAC_n and PCholMC_n were studied by DSC,POM and SAXS.The results showed that the liquid crystal property of PCholAC_n depended strongly on M_n.When M_n was less than 12.7×10³ g/mol,PCholACn was amorphous polymer.When M_n exceeded the critical point,PCholAC80 formed smectic A phase.However,M_n had little effect on the liquid crystal property of PCholMCn series polymers,all of which have formed a smectic A phase with interlaced tail chains?SmA₂?.2.Copolymers PCholAC-co-MA?n:m?and PCholAC-co-MA?n:m?were synthesized by copolymerization of cholesterol acrylate and cholesterol methacrylate with methyl acrylate by RAFT,respectively.Among them,n:m represents the molar ratio of monomer?methyl?cholesterol acrylate and methyl acrylate,respectively.The results showed that with the increase of methyl acrylate content,PCholAC-co-MA?n:m?showed the variation process from amorphous structure to LC phase structure to amorphous structure.For PCholMC-co-MA?n:m?,the copolymers have undergone a change from liquid crystal copolymers to amorphous copolymers.We hypothesized that methyl acrylate may affect the density of mesogenic and the flexibility of the whole molecular chain,so the molecular arrangement of these two types copolymers changed with the increase of the content of methyl acrylate.3.Three kinds of side-chain liquid crystalline polymers?SCLCPs?in which cholesteryl mesogens?Chol?were linked to polyacrylate backbone?PCholAC-m?,polymethacrylate backbone?PCholMC-m?and poly?2-vinylbenzene-1,4-dioate?backbone?PCholVA-m?by different lengths of methylene spacer?m=0,2,4,6,8 and10?,were successfully synthesized by free-radical polymerization.The results showed that Chol-SCLCPs exhibited interesting self-assembly behavior by changing the structure of main chain and the length of flexible spacer.Except for PCholAC-0,other polymers formed different smectic A phases under the influence of the structure of main chain and the length of flexible spacer.