Accessible Requires Authentication Published by De Gruyter June 6, 2013

Development of a Direct Polycondensation Process for Poly (L-lactic acid)

T. Fukushima, Y. Sumihiro, K. Koyanagi, N. Hashimoto, Y. Kimura and T. Sakai

Abstract

Poly(L-lactic acid) (PLLA) is quite promising for use as biodegradable and non-petroleum derived plastics. In this study we developed an innovative two-step polycondensation process so as to produce economically PLLA with high molecular weight. The process is composed of both melt polycondensation under the lactide-re ux and solid-phase polycondensation. First we studied a direct polycondensation of L-lactic acid with a small amount of solvent, using a mixture of L-lactic acid as raw material, diphenyl ether as solvent, Tin (II) chloride dihydrate as catalyst, and p-toluene sulfonic acid as a discoloration prevention agent. After the dehydrative oligomerization of L-lactic acid, the polycondensation of the oligocondensates and solid-phase post-polycondensation, PLLA of Mw = 266,000 could be obtained. Then, we carried out direct bulk polycondensation tests from L-lactic acid without any solvent added. After optimization of the reaction conditions, PLLA with Mw = 134,000 was successfully produced by the melt-poly-condensation of L-lactic acid accompanied by solid-phase post-poly-condensation. In both systems, the lactide-re ux was indispensable for promoting dehydration/water removal. The re uent lactide was taken into the polymer-chain by trans-esterification reaction during the melt-poly-condesation. Furthermore, the catalyst was allowed to deactivate and stabilize during the solid-phase polymerization to cause the Mw growth.


* Mail address: Prof. Dr. T. Sakai, The Japan Steel Works Ltd., 1-6-1 Funakoshi-minami, Aki-ku, Hiroshima, 736-8602 Japan

Received: 2000-4-17
Accepted: 2000-9-12
Published Online: 2013-06-06
Published in Print: 2000-12-01

© 2000, Carl Hanser Verlag, Munich