四臂聚乙二醇-左旋聚乳酸共聚物對左旋聚乳酸結晶行為之影響

Abstract

本研究主要探討添加四臂聚乙二醇以及四臂聚乙二醇-左旋聚乳酸共聚物，對左旋聚乳酸結晶行為的影響與結晶形態學上的變化。 四臂聚乙二醇因混摻的量少，不會參與左旋聚乳酸的結晶，而四臂聚乙二醇-左旋聚乳酸共聚物尾端有左旋聚乳酸鏈段，因此會參與左旋聚乳酸的結晶。從DSC、XRD以及POM的分析結果皆可發現，四臂聚乙二醇/左旋聚乳酸混摻物中，左旋聚乳酸結晶行為與形態學上的改變主要來自於PEG鏈段，混摻的量越多，PEG鏈段的影響越明顯；而在四臂聚乙二醇-左旋聚乳酸共聚物/左旋聚乳酸混摻物，就必須將PEG鏈段與星狀構型造成的影響一起考慮，共聚物/左旋聚乳酸的重量比5/95時，PEG鏈段的影響比星狀構性大，但當共聚物/左旋聚乳酸的重量比達到10/90時，有參與結晶的星狀構型的影響的幅度會比沒有參與結晶的PEG鏈段影響幅度還要大。 聚乳酸結晶時，會因結晶溫度不同而生成不同的結晶結構，在結晶溫度較高的區域，會形成排列較緊密的α結構，在結晶溫度較低時以排列較鬆散的α’結構居多，中間溫度為兩個結構共存的溫度區間。從XRD分析可知，四臂聚乙二醇/左旋聚乳酸混摻物，α結構可存在的溫度降低，是因為四臂聚乙二醇提升左旋聚乳酸的分子鏈運動能力，使得以分子鏈運動能力為影響主因的α結構在較低結晶溫度仍可出現；而四臂聚乙二醇-左旋聚乳酸共聚物/左旋聚乳酸混摻物與線性左旋聚乳酸的分子鏈運動能力差不多，但重量比10/90的混摻物，α結構可存在的溫度也降低，這是因為星狀構型使得α’結構競爭能力下降。添加混摻物後，α結構與α’結構的共存區間的改變，仍是動力學中不同因素互相競爭下的結果。

The focus of this research is to study the effect of crystallization behavior and crystal morphology of PLLA after adding 4-arm PEG and 4-arm copolymer. 4-arm PEG did not participate in the crystallization of PLLA due to the comparatively lower amount in the weight fraction of the blending. However, 4-arm copolymer was able to crystallize with PLLA, as it had PLLA chains at the end of the copolymer. From the result of DSC, XRD and POM analysis, many of the changes in the crystallization behavior and morphology of PLLA in the 4-arm PEG/PLLA blend were caused by the PEG chains. As the amount of 4-arm PEG was increased, the effects of the PEG chain became more evident. In the case of the 4-arm copolymer/PLLA blend, both effects of the star structure and the PEG chains were considered. The effects of the PEG chain were more apparent than those of the star structure in the blend of PLLA with 5 wt% of 4-arm copolymer. However, when the blending amount was increased to 10 wt%, a greater effect on the PLLA blend was observed due to the influence of the star structure. PLLA formed 2 different crystal structures under different crystallization temperatures. At higher crystallization temperatures, a densely packed α-crystal structure was formed, while at lower crystallization temperatures, the formation of a loosely packed α’-crystal structure was observed. Within the observed temperature range for crystal structure formation, both structures co-existed. From XRD analysis, the α-crystal was able to exist at lower crystallization temperatures after the incorporation of 4-arm PEG, as the PEG chain increased the chain mobility of PLLA. The chain mobility is the controlling factor for the formation of the α-crystal. The chain mobility was similar in the 4-arm copolymer/PLLA blend and pure PLLA, but when the blending amount of 4-arm copolymer was increased to 10 wt%, the α-crystal was also able to exist at lower crystallization temperatures. This was due to the fact that the star structure caused the α’-crystal structure to be less competitive towards the α-crystal structure. In conclusion, the α-crystal and α’-crystal structures were co-existent at a range of temperatures where the upper limit was achieved when the α-crystal structure was fully dominant and the lower limit was achieved when the α’-crystal structure was fully dominant. This yielded an effect where α-crystal and α’-crystal structures co-existed on a gradient at which higher temperatures favored an α-crystal structure and lower temperatures favored an α’-crystal structure. Thus, it was determined that the effects of adding 4-arm PEG and 4-arm copolymer allowed for the shifts in the temperature ranges as a result of kinetics.