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Melt polycondensation of L ‐lactic acid catalyzed by 1,3‐dialkylimidazolium ionic liquids
Author(s) -
Wang Weichao,
Wu Linbo,
Huang Yuan,
Li BoGeng
Publication year - 2008
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.2421
Subject(s) - catalysis , ionic liquid , lactic acid , condensation polymer , yield (engineering) , chemistry , toluene , crystallinity , cationic polymerization , polymer chemistry , polymer , pyridine , organic chemistry , materials science , biology , bacteria , metallurgy , genetics , crystallography
Abstract BACKGROUND: In syntheses of biodegradable and bioresorbable polymers, efficient metal‐free catalysts are very desirable as the resulting products may be more biocompatible. As an attempt to find new metal‐free catalysts, 1,3‐dialkylimidazolium salts, the most commonly used ionic liquids or organic melt salts, were used as single‐component catalysts in the melt polycondensation of L ‐lactic acid for the first time. The resulting poly( L ‐lactic acid) (PLLA) was characterized using gel permeation chromatography, 13 C NMR, DSC and polarimetry. RESULTS: It has been found that less bulky substituents on the imidazolium ring are conducive to catalytic activity. PLLA with molar mass of about 20 000 g mol −1 was synthesized at high yield (over 70%) in the presence of various 1,3‐dialkylimidazolium salts. The product exhibits satisfactory color (white to slightly yellow), optical purity (89–95%) and crystallinity (40–55%). A possible catalytic mechanism is proposed. CONCLUSION: As compared with the well‐known binary catalyst system SnCl 2 · 2H 2 O/toluene sulfonic acid, the catalysts used in this investigation are better in terms of increasing PLLA yield and preventing discoloration and comparable in terms of racemization. Copyright © 2008 Society of Chemical Industry