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通过阳离子活性开环聚合和大分子酯化反应的两步法,合成两亲性的聚消旋丙交酯-b-聚氧乙烯(sPDLLA-b-PEO)六臂星形嵌段聚合物。通过差示扫描量热法研究了聚合物本体结晶行为。结果表明,无定形链段PDLLA的引入和特定的星形结构,使得PEO链段的结晶受到限制,出现了冷结晶现象,并且最高结晶温度随着升温速率的增大而升高。通过偏光显微镜研究了六臂嵌段聚合物的结晶形貌,发现六臂sPDLLA-b-PEO生长产生环带球晶。并且通过调控聚合物与溶剂的比例和聚合物膜的厚度,发现溶剂可以减小球晶生长中积累的应力,使环带结构消失;但六臂聚合物对于几何受限的响应性较强,当膜厚减小时,环带结构重新出现。
Amphiphilic poly (lactide-co-b-polyoxyethylene) (sPDLLA-b-PEO) six-arm radial block copolymer was synthesized by a two-step process of cationic living ring-opening polymerization and macromolecular esterification. The crystallization behavior of polymer bulk was studied by differential scanning calorimetry. The results show that the introduction of amorphous PDLLA and the special star structure make the crystallization of PEO chain limited, resulting in the phenomenon of cold crystallization, and the highest crystallization temperature increases with the increase of heating rate. The crystal morphology of the six-armed block copolymer was studied by polarized light microscope. It was found that the six-armed sPDLLA-b-PEO grew and produced ring-shaped spherulites. And by adjusting the ratio of polymer to solvent and the thickness of the polymer film, it is found that the solvent can reduce the stress accumulated in the spherulites growth and make the ring structure disappear. However, the six-arm polymer has strong responsiveness to geometric constraints, When the film thickness decreases, the band structure reappears.