Crystallization behavior and thermal properties of biodegradable poly(L-lactide)-poly(ethylene glycol) block copolymers
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Hawn-Chung Chua) Department of Chemical and Materials Engineering, Lee-Ming Institute of Technology, Taishan, New Taipei City, Taiwan, Republic of China
Li-Huei Lin Department of Cosmetic Science, Vanung University, Chung-Li City, Tao-Yuan County, Taiwan, Republic of China
Jia-He Wu Department of Materials Science and Engineering, Vanung University, Chung-Li City, Tao-Yuan County, Taiwan, Republic of China (Received 1 July 2012; accepted 26 February 2013)
This study presents a polymerization of L-lactide and poly(ethylene glycol) of various molecular weights to produce biodegradable poly(L-lactide)-poly(ethylene glycol) (L-PEG) block copolymers. The chemical structures, crystallization behavior and thermal properties of L-PEG copolymers were investigated using proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, thermogravimetric analysis and differential scanning calorimetry (DSC). The analysis of isothermal crystallization behavior of L-PEG copolymers using the Avrami equation revealed that the grain growth of L-PEG200 and 600 were unstable, jumping between one dimension and two dimensions. By contrast, the grain growth of L-PEG2000 was more stable, with a growth trend toward three dimensions. The results of L-PEG isothermal crystallization by DSC indicate that within a range of 123–127 °C, the crystallization rate was higher at lower temperatures. The values of the crystallization constants in the Avrami equation were also lower.
I. INTRODUCTION
Poly(lactic acid) (PLA) not only possesses biodegradability and biocompatibility1–5 but also exhibits good physical and mechanical properties.3,4 However, flexibility1 is its chief defect which limits its scope for practical applications. It is noteworthy that the amount of D-lactic acid affects the melting point and crystallinity of PLA, and also has a great effect on its physical and degradable properties.3 Poly(ethylene glycol) (PEG), which has excellent physical and biomedical properties,2,5 such as hydrophilicity, biocompatibility, nontoxicity and nonimmunogenicity, is often used as an ingredient of biomedical and pharmacological materials. Recently, some reports2,5–8 have been published on special block copolymers, which were synthesized from poly(L-lactic acid) (PLLA) and PEG by melting polymerization and possess their chemical structures by virtue of having two or three blocks. The prepared copolymers had distinctive properties on biomedical applications because the PLLA was the main chain of the copolymer structure. Not only the chemical structures, molecular weights and their distributions have a great effect on the crystallization a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.47 J. Mater. Res., Vol. 28, No. 8, Apr 28, 2013
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behavior but also the crystallization conditions and kinetic mechanisms play important roles in the crystallization processes. The crystallization processes can
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