Synthesis And Characterization Of Aliphatic Polycarbonate Containing Side Chain Biomesogenic Groups

In recent years,biomedical polymer materials,mainly including aliphatic polycarbonates with functional groups,have attracted considerable interest due to their many advantages in the biological disease diagnosis,treatment,and repair or replacement of biological tissues and organs.It is known that cholesterol is a fundamental composition of mammalian membranes,and it has special structure with many chiral carbon atoms,and is easier to be modified by other groups.So as a kind of chiral mesogenic unit,these characteristics make cholesterol an interesting component in many areas.It is necessary to synthesize polycarbonates containing biological cholesteryl side groups to combine the biodegradability of aliphatic polycarbonates with the good properties of biological liquid crystals such as orientation,mechanical property and biological compatibility etc.Moreover,new liquid crystal biodegradation polycarbonates with excellent performance and wide application are expected to obtain in this study.In the second chapter,four liquid crystal intermediate compounds with terminal hydroxyl groups were synthesized by reacting cholesterol with 1,2-ethanediol,1,4-butanediol,1,6-hexanediol,and 1,8-octanediol,respectively in the present of 4-methyl-benzene-sulfonylchlorid,which were named as 2-cholesteroxyethanol（C₁）,4-cholesteroxybutan-l-ol（C2）,6-cholesteroxyhexan-l-ol（C₃）,and 8-cholesteroxyoctan-l-ol（C₄）.The structure of four intermediate compounds was different in flexible methylene length,and characterized by FT-IR and 1H NMR.Their thermal properties and optical textures were investigated by DSC,polarizing optical microscopy（POM）,and X-ray diffraction（XRD）.The compounds C₁-C₄ all showed enantiotropic mesophase,and C₁ only exhibited the fan-shaped texture of a smectic phase,C2-C₄ showed the fan-shaped texture of a smectic phase,and oily-streak and focal conic textures of cholesteric phase.With an increase of methylene length,the melting temperature（Tm）,the transition temperature between different mesophase,and the clearing temperature（Ti）showed a decreasing trend.In addition,the corresponding Ti decreased more than Tm,so the mesophase temperature ranges widened.In the third chapter,the homopolymer PMBC,amphiphilic block copolymer mPEG-b-PMBC,and triblock copolymer mPEG-b-PMBC-b-PCL were synthesized by reacting the compounds 5-methyl-2-oxo-1,3-dioxane-5-carboxylate（MBC）,poly（ethylene glycol）monomethyl ether（mPEG）,and 1-oxa-2-oxocycloheptane（CL）using stannous octanoate as an initiator.Then,the protective benzyl groups in polycarbonate side chains were removed by catalytic hydrogenolysis using Pd/C and Pd（OH）2/C as catalyst under hydrogen atmosphere to obtain the polycarbonate with side carboxyl groups,which were PMCC,mPEG-b-PMCC,and mPEG-b-PMCC-b-PCL.The structure and thermal properties of the polymers were characterized by FT-IR,1H NMR,and DSC.The results showed that the introduce of mPEG and PCL into polycarbonate main chains made the glass transition temperature（Tg）decrease.In the fourth chapter,four new amphiphilic block copolymers（mPEG-b-P（MCC-C₁）—mPEG-b-P（MCC-C₄））were obtained by reacting four cholesteryl derivatives with mPEG-b-PMCC,respectively.Moreover,the polymers P（MCC-C₃）and mPEG-b-P（MCC-C₃）-b-PCL were prepared by reacting C₃ with PMCC and mPEG-b-PMCC-b-PCL,respectively.The structure of six new liquid crystal polymers was characterized by FT-IR,and their thermal properties and optical textures were characterized by DSC and POM.The results showed that mPEG-b-P（MCC-Ci）and mPEG-b-P（MCC-C2）exhibited liquid crystal properties only on heating process,other four polymers all showed mesomorphism on heating and cooling cycles.With an increase of methylene length,the Tg and Ti showed an increasing trend and the mesophase temperature ranges widened.The introduce of mPEG and PCL into polycarbonate main chains made the mesophase temperature ranges of P（MCC-C₃）widen.