Synthesis And Characterization Of The Bioabsorbable Cholesteric Liquid Crystal Material

Cholesterol acts as an active substance in vivo, having the thermodynamic affinity for cellmembranes, tailoring the bilateral structure of the phospholipid membrane and dynamicsbehavior of physiology. Meanwhile, the cholesterol derivatives usually have the ability to formliquid crystal phase. Therefore, cholesterol-modified material can promote cell attachment aswell as cell proliferation.Poly（ethylene glycol）（PEG） has been regarded as possessing good biocompatibility, non-toxic,and low immunogenicity. The activation of the terminal hydroxy groups of polyethylene glycolcan be modified and provide a new performance on a new material. In this paper, two approachnamely "one pot" and "click" chemistry were used to prepare cholesterol-poly （ethylene glycol）oligomers and cholesterol-（1,2,3-triazole）-poly（ethylene glycol） oligomers, and the liquid crystalproperties of the oligomers were also evaluated.Firstly, cholesterol-poly（ethylene glycol） oligomers with different molecular weight weresynthesized through "one pot" method, and the liquid crystal properties of oligomers werestudied.The first part, toluene sulfonyl groups was introduced into cholesterol by the reaction ofcholesterol and p-toluenesulfonyl chloride, and then two different molecular weightcholesterol-poly （ethylene glycol） oligomers were prepared by the reaction of polyethyleneglycol (PEG=M_w194, M_w400) and toluenesulfonyl cholesterol, the structure of the products werecharacterized by FT IR,1H NMR, the liquid crystal behaviors of the products were verified byDSC, POM and SAXS analysis. The results show that the molecular weight of the twocholesterol-poly （ethylene glycol） oligomers synthesized by the "one pot" method is closed to thetheoretical value. The molecular weight of polyethylene glycol plays an important role in liquidcrystal properties. The liquid crystal transition temperature and liquid crystal range is related tothe molecular weight of cholesterol-poly（ethylene glycol） oligomers.The second part,cholesterol-（1,2,3-triazole）-poly（ethylene glycol） oligomers with two differentmolecular weight (PEG=M_w194, M_w400) were synthesized through "click" chemistry process, andthe liquid crystal properties of oligomers were studied.Firstly, cholesterol was modified by the reaction of cholesterol and p-toluenesulfonyl chloride,and the azide group was introduced into cholesterol by the reaction of sodium azide and toluenesulfonyl cholesterol, and then the alkyne was introduced into polyethylene glycol(PEG=M_w194, M_w400) by the reaction of PEG and bromine propargyl. Cholesterol-（1,2,3-triazole）-poly（ethylene glycol） were synthesized by "click" chemistry, through PEG with differentmolecular weight.The structure of the products were characterized by the FT IR,1H NMR, theliquid crystal behaviors of the products were analyzed by DSC,POM and SAXS analysis. Theresults show that the molecular weight of cholesterol-（1,2,3-triazole）-poly（ethylene glycol）oligomers synthesized by "click" chemistry is closed to the theoretical value. The molecularweight of polyethylene glycol plays an important role in liquid crystal properties. The liquidcrystal transition temperature and liquid crystal range is related to the molecular weight ofcholesterol-（1,2,3-triazole）-poly （ethylene glycol） oligomers.The result shows that the cholesterol-poly（ethylene glycol） oligomers and cholesterol-（1,2,3-triazole）-poly （ethylene glycol） oligomers with different molecular weight of PEG were preparedsuccessfully. The liquid crystal properties were observed obviously through DSC,POM and thedifferent liquid crystal properties of these materials can be changed by tailoring the chain lengthof polyethylene glycol.