Melt Polycondensation and Analysis of Hydroxyl-Terminated Poly(L-lactic Acid) Using Small Molecular Diols as Terminating Agents

Abstract:

The synthesis of hydroxyl-terminated poly (L-lactic acid) (PLLA) by direct melt polycondensation of L-lactic acid and use of small molecular diols as terminating agents was investigated. L-lactic acid was dewatered to prepare the dehydrated prepolymer at first. Then PLLA was prepared through melt polycondensation in a melt with catalyst system including TSA, SnCl₂ and Sn (Oct)₂. Finally, ethylene glycol, 1,4-butanediol, and 1,8-octanediol, respectively, were used in hydroxyl termination of the PLLA. The molecular weights and end-group structures of all products were characterized by gel permeation chromatography (GPC) and ¹H-NMR. DSC and Disc Polarimeter were used to characterize crystallinity and racemization, respectively. The results show that two kinds of hydroxyl-terminated PLLA polymers were obtained: complete hydroxyl-terminated PLLA prepared by using ethylene glycol or 1,4-butanediol, incomplete hydroxyl-terminated PLLA prepared by using 1,8-octanediol or combination of two kinds of diols. Combination of ethylene glycol or 1,4-butanediol with 1,8-octanediol can reach high hydroxyl termination of PLLA, and maintain the molecular weight by decrease of alcoholysis at the same time. ¹H-NMR was found as an effective estimating way for extents of reactions. The hydroxyl-terminating reactions of PLLA by the diols reduced the crystallinity and resulted in racemization to some extent.

• Periodical: Applied Mechanics and Materials (Volume 328)
• Pages: 890-894
• DOI: https://doi.org/10.4028/www.scientific.net/AMM.328.890
• Online since: June 2013
• Authors: Jing Che, Rong Jie Yang
• Keywords: Diols, Hydroxyl-Terminated, Melt Polycondensation, Poly(L-lactic acid)

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