三嵌段刷状共聚物的合成及溶液组装制备多孔纳米粒子

Synthesis of Triblock Bottlebrush Copolymer and Its Solution Self-assembly to Form Porous Nanoparticles

结合可控自由基聚合和铜催化的叠氮-炔环加成(Cu AAC)反应,合成了coil-brush-coil型三嵌段刷状共聚物.其中coil段为亲水性的聚(N,N′-二甲基丙烯酰胺)(PDMA),brush段为高密度接枝V形侧链的疏水性聚丙烯酸酯.由于其两亲性特征及刷状拓扑结构所赋予的主链刚性,该嵌段共聚物在选择性溶剂甲醇和乙醇中可分别自组装得到片状胶束和囊泡.刷状嵌段的V形侧链包含聚苯乙烯(PS)和聚左旋丙交酯(PLLA)2条链,它们在胶束(或囊泡)组装体的核(或壁)区发生微相分离得到有序的柱状相分离形貌.将离散柱状PLLA相水解,即可得到核或壁具有多孔结构的片状胶束或囊泡.

A triblock bottlebrush copolymer, poly（N,N-dimethyl acrylamide）-block-（polyacrylate-graft-（polystyrene-alternate-poly（L-lactide）））-block-poly（N,N-dimethyl acrylamide）（PDMA-b-（PA-g-（PS-alt-PLLA））-b-PDMA）, was prepared with an amphiphilic coil-rod-coil macromolecular structure based on the combination of reversible addition-fragmentation chain transfer polymerization（RAFT）, copper-catalyzed azide-alkyne cycloaddition reaction（Cu AAC）, and ring-opening polymerization（ROP）. For the formation of the triblock bottlebrush copolymer,RAFT was used to prepare the well-defined triblock copolymer main chain of PDMA-bPA-b-PDMA.Cu AAC was then employed to graft the PS side chains onto the reactive PA block to form the triblock bottlebrush copolymer PDMA-b-（PA-g-PS）-b-PDMA with PS side chains.The in situ ROP of L-lactide to graft PLLA from PA block finally produced the triblock bottlebrush copolymer of PDMA-b-（PA-g-（PS-altPLLA））-b-PDMA with V-shaped side chains of PS and PLLA.In this macromolecule,PDMA formed the hydrophilic coil blocks while the bottlebrush polymer of PA-g-（PS-alt-PLLA）formed the hydrophobic rod block.Self-assembly of the amphiphilic PDMA-b-（PA-g-（PS-alt-PLLA））-b-PDMA was subsequently investigated in selective solvents.Due to the unique coil-rod-coil molecular structure,this triblock bottlebrush copolymer selfassembled into sheet-like micelles or vesicles in the selective solvents of THF/methanol or THF/ethanol,respectively.In these self-assemblies,the coil hydrophilic PDMA block formed the dispersing shell to keep their dispersion while the rigid hydrophobic bottlebrush block aggregated into the sheet-like cores to maintain stability of the self-assemblies.The PS and PLLA side chains with V-shaped structure along the middle blocks microphase-separated inside the aggregated micellar sheet or vesicle wall,in which the isolated PLLA microdomain was surrounded by the continuous PS microdomain.Furthermore,the selective hydrolysis of PLLA microdomain left the nanopores inside the cores of micelles and vesicles.It has been demonstrated the hydrolysis rate was heavily depended on the morphology of the self-assemblies,where the hydrolysis of PLLA microdomains of sheet-like micelles was much faster than that of the corresponding vesicles.