聚乙二醇-聚L-丙交酯嵌段共聚物结晶形貌研究

用偏光显微镜和原子力显微镜对比研究了PEG-PLLA嵌段共聚物在110℃或120℃等温结晶后的结晶形貌.发现在110℃时只有PEG5000-PLLA2300和PEG5000-PLLA6300在偏光显微镜下呈现环带球晶形貌,在原子力显微镜高度图中显示明显的环带,并具有交替凸凹起伏形貌.而PEG5000-PLLA12000球晶中没有出现环带形貌而是生成了规则的环线.在120℃时,PEG5000-PLLA12000的球晶中才生成了规则的环带图案,原子力显微镜也显示了其球晶具有明显的交替凸凹起伏形貌,说明过冷度直接影响环带球晶的生成.产生周期性凸凹起伏和明暗交替消光是由片晶沿着球晶的半径方向周期性扭转造成的,片晶在凸起部分是Edge-on取向,在凹下部分是Flat-on取向.

Studies on Crystalline Morphology of Poly(L-lactide)-Poly(ethylene glycol) Diblock Copolymers

Crystallization behavior and morphology development in biodegradable diblock copolymers of poly(L-lactide)-poly(ethylene glycol)(PLLA-PEG) have been investigated by means of polarized optical microscopy(POM) and atomic force microscopy(AFM). At 110 ℃, PEG5000-PLLA2300 and PEG5000-PLLA6300 diblock copolymers formed banded spherulites, while PEG5000-PLLA12000 did not give banded spherulites. At 120 ℃, PEG5000-PLLA12000 formed banded spherulites, too, indicating that suitable undercooling is one of the key factors to get these banded spherulites. As a solvent and a diluting agent, the presence of PEG blocks brings about decrease in nucleation rate and increase in growth rate of the PLLA crystallization at around 110 ℃, resulting in larger spherulites. The surface of the banded spherulite is shown to consist of concentric ridges and valleys. At the ridges, PLLA lamellae were stacked in edge-on manner, while at the valleys, PLLA lamellae were stacked in flat-on manner.