Study of the synthesis, crystallization, and morphology of poly(ethylene glycol)-poly(∈-caprolactone) diblock copolymers
Study of the synthesis, crystallization, and morphology of poly(ethylene glycol)-poly(∈-caprolactone) diblock copolymers
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DOI：
10.1021/bm049720e
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发表时间：
2004-09-01
影响因子：
6.2
通讯作者：
Jing, XB
中科院分区：
文献类型：
--
作者：
He, CL;Sun, J;Jing, XB
以单甲氧基聚乙二醇为大分子引发剂，氨化钙为催化剂，通过开环聚合法合成了聚乙二醇-聚己内酯（PEG-PCL）嵌段共聚物。通过改变嵌段相对长度，研究了PEG和PCL结晶之间的相互影响。固定PEG嵌段的长度（M-n = 5000）并增加PCL嵌段的长度，PCL嵌段的结晶温度从1 ℃逐渐上升到约35 ℃，而PEG嵌段的结晶温度从36 ℃下降到-6.6 ℃。同时，PCL嵌段的熔融温度从30 ℃上升到60 ℃，而PEG嵌段的熔融温度从60 ℃下降到41 ℃。如果PCL嵌段比PEG嵌段长，则当从熔融状态冷却时，前者将首先结晶并且导致PEG的明显不完全结晶，反之亦然。如果它们的重量分数相等，它们在相同的温度下结晶。我们发现，PEG嵌段在-6.6 ℃下仍能结晶，即使其重量分数仅为14%。观察到PEG 5000-PCL 5000的同心球晶的独特形态。根据它们的形态和实时生长速率，可以得出结论，在同心球晶的中心和外部部分分别是PCL和PEG，并且在同心球晶的形成过程中，PEG在早期阶段从PCL晶体的自由空间快速结晶，随后从PCL球晶沿与圆边界成直角的方向向外生长，直到占据整个区域。
Poly(ethylene glycol) -poly(epsilon-caprolactone) diblock copolymers PEG-PCL were synthesized by ring-opening polymerization of c-caprolactone using monomethoxy poly(ethylene glycol) as the macroinitiator and calcium ammoniate as the catalyst. Obvious mutual influence between PEG and PCL crystallization was studied by altering the relative block length. Fixing the length of the PEG block (M-n = 5000) and increasing the length of the PCL block, the crystallization temperature of the PCL block rose gradually from I to about 35 degreesC while that of the PEG block dropped from 36 to -6.6 degreesC. Meanwhile, the melting temperature of the PCL block went up from 30 to 60 degreesC, while that of the PEG block declined from 60 to 41 degreesC. If the PCL block was longer than the PEG block, the former would crystallize first when cooling from a molten state and led to obviously imperfect crystallization of PEG and vice versa. And they both crystallized at the same temperature, if their weight fractions were equal. We found that the PEG block could still crystallize at -6.6 degreesC even when its weight fraction is only 14%. A unique morphology of concentric spherulites was observed for PEG5000-PCL5000. According to their morphology and real-time growth rates, it is concluded that the central and outer sections in the concentric spherulites were PCL and PEG, respectively, and during the formation of the concentric spherulite, the PEG crystallized quickly from the free space of the PCL crystal at the earlier stage, followed by outgrowing from the PCL spherulites in the direction of right angles to the circle boundaries until the entire area was occupied.