Synthesis And Characterization Of Amphipathic Block Polymers Based On Polycarbonate Containing Diosgenyl Groups

In recent years,the aliphatic polycarbonates have attracted much attention due to their good biodegradability and biocompatibility in the field of medicine and life science.As known,liquid crystal(LC)materials have self-organization orientation,and can form the ordered structure by self-assembly under external stimuli,such as temperature,pressure,magnetic fields,etc.The aliphatic LC polycarbonates combine good biodegradability of polycarbonates with multi-responsive properties of LC materials,and have received more and more attention and application in the field of materials science and biomedicine.Diosgenin has multiple biological activity and is a natural mesogenic unit.However,to the best of our knowledge,no research has been reported on functional aliphatic LC polycarbonates containing diosgenyl groups.The main idea of this study is to introduce diosgenyl group into aliphatic polycarbonate chains and obtain amphiphilic block functional macromolecules.On the one hand,it can provide a model to explore life in multi-scale orderly functional structures,on the other hand,has become an attractive candidate to synthesize new smart,responsive,medical biodegradable materials with stimuli-response behavior.In the second chapter,three LC intermediate compounds with terminal hydroxyl groups and different flexible spacer were synthesized by reacting diosgenin with 1,4-butanediol,1,6-hexanediol and 1,8-octanediol,respectively,in the presence of 4-methyl-benzene-sulfonylchlorid.These intermediate compounds were named as 4-diosgenoxybutane-l-ol(C1),6-diosgenoxyhexane-l-of(C2)and 8-diosgenoxyoctane-l-of(C3).Their structures were characterized by FT-IR and 1H NMR.The optical texture and mesophase structures were investigated by polarizing optical microscopy(POM)and X-ray diffraction(XRD).C1-C3 all showed enantiotropic mesophase;C1 exhibited the focal conic textures of cholesteric phase,however,C2 and C3 exhibited the fan-shaped textures of a smectic A phase.The molecular modelling calculation suggested that the molecular arrangements of C2 and C3 were single layer.Thermal properties were investigated by differential scanning calorimetry(DSC).The results indicated that the melting temperature(Tm)and the clearing temperature(Ti)showed a decreasing trend with increasing flexible spacer length.In the third chapter,the compound benzyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate(MBC)was first synthesized.Secondly,three amphiphilic block copolymers(mPEG43-b-PMBC40,mPEG43-b-PMBC49 and mPEG43-b-PMBCs7)with different polymerization degree were obtained through the ring-opening polymerization of MBC using Sn(Oct)2 as a catalyst in the presence of mPEG as a macroinitiator.Finally,the block copolymers(mPEG43-b-PMCC40,mPEG43-b-PMCC49 and mPEG43-b-PMCC57)with side carboxyl groups were obtained by hydrogenolysis reaction to result in the deprotection of side benzyl groups using Pd/C and Pd(OH)2/C as catalysts under hydrogen atmosphere The structures and thermal properties of six polymers were characterized by FT-IR,1H NMR and DSC,respectively.The results showed that the glass transition temperatures(Tg)of six polymers increased with increasing the degree of polymerization.In the fourth chapter,a new amphiphilic block copolymer mPEG43-b-P(MCC-C2)40 was prepared through a coupling reaction between side carboxyl group of mPEG43-b-PMCC4o and the terminal hydroxyl group of C2.The structure,optical texture and thermal property of mPEG43-b-P(MCC-C2)40 were characterized by FT-IR,1H NMR,POM and DSC,respectively.The results indicated that mPEG43-b-PMCC4o showed good mesomorphism on heating and cooling cycles.Then,the hydrophilicity of mPEG43-b-P(MCC-C2)40 was studied using contact angle measuring device,and it was a hydrophilic compound.The self-assembly process of mPEG43-b-P(MCC-C2)40 in THF/H2O was monitored by UV-Vis,the average radius and morphologies of the aggregates self-assembled by mPEG43-b-P(MCC-C2)40 in THF/H2O were investigated by dynamic light scattering(DLS)and scanning electron microscope(SEM),respectively.The results indicated that polymer vesicles were formed in THF/H2O by the block copolymer mPEG43-b-P(MCC-C2)40,and the average radius of the vesicles was 121.8 nm(PDI:0.119).