Preparation of high-molecular-weight poly(L-lactic acid)-based polymers through direct condensation polymerization in bulk state

Abstract

Poly(L-lactic acid-co-succinic acid-co-1,4-butanediol) (PLASB) was synthesized by a direct condensation copolymerization of L-lactic acid, succinic acid (SA), and 1,4-butanediol (BD) in bulk state using titanium(IV) butoxide (TNBT) as a catalyst. Weight average molecular weight (Mw) of PLASB increased from 3.5 × 104 to 2.1 × 105 as the content of SA and BD went up from 0.01 to 0.5 mol/100 mol of L-lactic acid (LA). PLASB having Mw in the range from 1.8 × 105 to 2.1 × 105 showed tensile properties comparable to those of commercially available poly(L-lactic acid) (PLLA). In sharp contrast, homopolymerization of LA in bulk state produced PLLA with Mw as low as 4.1 × 104, and it was too brittle to prepare specimens for the tensile tests. Mw of PLASB synthesized by using titanium(IV)-2-ethyl(hexoxide), indium acetate, indium hydroxide, antimony acetate, antimony trioxide, dibutyl tin oxide, and stannous-2-ethyl 1-hexanoate was compared with that of PLASB obtained by TNBT. Ethylene glycol oligomers with different chain length were added to LA/SA in place of BD to investigate effect of chain length of ethylene glycol oligomers on the Mw of the resulting copolymers. Biodegradability of PLASB was analyzed by using the modified Sturm test. Toxicity of PLASB was evaluated by counting viable cell number of mouse fibroblast cells that had been in contact with PLASB discs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 466–472, 2006