The use of different diols in the synthesis of low-molecular-weight lactic-acid-based telechelic prepolymers

Abstract

The synthesis of low-molecular-weight (Mw (GPC) < 72000 g mol) lactic-acid-based telechelic prepolymers by condensation polymerization of L-lactic acid was investigated. All polymerizations were carried out in the melt, using tin(II)octoate as catalyst, different diols, and different polymerization temperatures. The products were characterized by differential scanning calorimetry (DSC), gel permeation chromatogra-phy (GPC), titrimetric methods, and 13C nuclear magnetic resonance (NMR). Accordingto NMR, the resulting polymers contained less than 1 mol % of lactic acid monomer and less than 8.5 mol % of lactide. The weight-average molecular weights of prepared prepolymers determined by GPC varied from 3800 to 72,000 g mol, depending on the diol and the polycondensation conditions. In DSC studies, the glass transition temperatures of the resulting polymers varied from 27 to 50°C, and the crystallinity from 0 to 51.8%. When aromatic diols were used in polymerizations, the location of hydroxyl groups had a strong effect on the properties of the final prepolymer. According to our results, the aromatic diols produced higher-molecular-weight prepolymers when the hydroxyl groups were located so that the polyester chains could grow in opposite directions. The introduction of a heteroatom raised the glass transition temperature of the prepolymer. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 67:1017–1023, 1998