The Influence of Isosorbide on Thermal Properties of Poly(L-lactide) Synthesized by Different Methods

In this article, we analyzed the influence of isosorbide content on glass transition temperature and crystallinity of poly(L-lactide). Different synthesis methods were applied to determine optimal procedure for polymerization of L-lactide in the presence of isosorbide. Two procedures were performed with tin(II) 2-ethylhexanoate as the catalyst: first, using the vacuum sealed vessel, and second, using microwave reactor bulk polymerizations. The solution polymerization (with trifluoromethanesulfonic acid as catalyst) was possible at the temperature of 40 degrees C. Obtained polyesters had number average molecular weights ranging from 20,000 to 65,000 g mol(-1), according to the gel permeation chromatography measurements. The polymer structure was characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. Thermal properties of the obtained polymers were analyzed using thermogravimetry (TG) and differential scanning calorimetry (DSC). According to DSC measurements, the addition of isosorbide in the polyesters influenced the increase in both glass transition temperature and degree of crystallization for all samples. The results obtained by thermogravimetric analysis confirmed the strong influence of polymerization mechanism on synthesized poly(L-lactides) thermal properties. (C) 2012 Society of Plastics Engineers