具有侧挂胆固醇液晶元的两亲嵌段功能大分子的合成及自组装研究

Preparation of New Amphiphilic Liquid-Crystal Diblock Copolymers Bearing Side-on Cholesteryl Mesogen and Their Self-aggregation

采用可逆加成-断裂链转移(RAFT)聚合法,合成了系列具有刚性疏水胆固醇液晶元的聚甲基丙烯酸甘油酯-嵌段-聚甲基丙烯酸亚己基胆固醇酯(PGMA-b-PMA6Chol)两亲嵌段功能大分子.运用核磁共振(NMR)和凝胶渗透色谱(GPC)表征了其化学结构及分子量,并对其热性质、液晶相结构及相转变行为分别运用热台偏振光显微镜(POM)、热重分析仪(TGA)、示差扫描量热仪(DSC)和二维小角X射线散射(2D-SAXS)表征.采用纳米沉淀法研究了所得嵌段大分子的溶液自组装,动态光散射(DLS)和扫描电子显微镜(SEM)的研究发现溶液自组装聚集体为尺寸0.7～2.0μm的球形结构,其中含有较高刚性链段质量比例的嵌段大分子组装形成开口中空结构的聚集体,且其尺寸随着溶液温度的升高减小,呈现可逆温度变化响应性.结果表明刚性疏水胆固醇液晶单元和具有多羟基结构的亲水性甲基丙烯酸甘油酯的嵌段共聚可以调控该类嵌段大分子自组装及溶液聚集体形貌.

Amphiphilic block copolymers bearing rigid hydrophobic liquid crystal mesogen have recently attracted broad interests since they could spontaneously self-assemble into functional objects at the micron and/or nanometer scales,and these soft matters bearing high-order hierarchical structures have potential applications in micro-reactors,advanced catalysts,biosensors,drug delivery,biotechnology and so forth.In this work,we designed and successfully prepared a new series of amphiphilic liquid crystal poly（glyceryl methacrylate）-b-poly（6-cholesteryloxyhexyl methacrylate）（PGMA-b-PMA6Chol） with hydrophobic PMA6Chol block bearing end-on cholesteryl mesogen through sequential controlled reversible additionfragmentation chain transfer polymerization（RAFT） and successive removal of ketal protection groups.Then,their structures and comonomer composition were examined by nuclear magnetic resonance（NMR） and gel permeation chromatography（GPC）.Liquid crystal phase structures and their transition as well as thermal stability of the prepared LC copolymers were characterized by differential scanning calorimeter（DSC）,polarized optical microscope（POM）,2D small angle X-ray scattering（2D-SAXS） and thermogravimetric analytic instrument（TGA）.Moreover,self-aggregation of these amphiphilic LC block copolymers in mixed solution was investigated by means of UV spectrometer,and the aggregate sizes and morphologies were examined by scanning electron microscopy（SEM） and dynamic light scattering（DLS）,respectively.As a result,it was revealed that the LC to isotropic phase transition temperature（TLC-I） of as-synthesized LC block copolymers increased with an increase in rigid LC block content,and the presence of bishydroxyl groups of hydrophilic PGMA strongly influenced the self-assembly and LC phase of rigid hydrophobic block in bulk state.In mixed solvent,the synthesized amphiphilic LC copolymers were found to preferably self-aggregate into core-shell spherical objects with average sizes spanning a range from 0.7 to 2.0 μm when the hydrophobic LC block content was less than 93%,in contrast,the LC copolymer with 93 wt% LC block tended to form open hollow spherical aggregates,showing interesting thermal responsive particle sizes in aqueous solution.