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International Journal of Polymer Science
Volume 2013, Article ID 315917, 6 pages
http://dx.doi.org/10.1155/2013/315917
Research Article

Preparation of Higher Molecular Weight Poly (L-lactic Acid) by Chain Extension

Key Laboratory of Rubber-Plastics, Ministry of Education/Shandong Provincial Key Laboratory of Rubber-Plastics, Qingdao University of Science & Technology, Qingdao 266042, China

Received 7 June 2013; Accepted 18 July 2013

Academic Editor: Zhou Yang

Copyright © 2013 Chenguang Liu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

High molecular weight poly (lactic acid) (PLA) was obtained by chain extending with hexamethylene diisocyanate (HDI). The influences of the amount of chain extender, reaction time, and molecular weight changes of prepolymers on the poly(lactic acid) were investigated. PLA prepolymer with a viscosity, average molecular weight ( ) of 2 × 104 g/mol was synthesized from L-lactide using stannous octoate as the catalyst. After 20 min of chain extension at 175°C, the resulting polymer had of 20.3 × 104 g/mol and of 10.5 × 104 g/mol. Both FT-IR and 1H-NMR verified that the structure of PLA did not change either before chain extending or after. The optically active characterized that the chain extending-product was left handed. DSC and XRD results showed that both the and the crystallinity of PLA were lowered by chain-extension reaction. The crystalline transformation happened in PLA after chain extending, crystalline form to form.