The main goal of this work was to obtain poly(L- lactic acid) homopolymers with different molecular weights via direct polycondensation of lactic acid at different polycondensation temperatures and times. Also the aim of this study was to develop a methodology to examine the kinetics of polycondensation reactions in order to estimate the mass transfer influence and to optimize reaction conditions. The PLLAs were characterized by ¹³C-NMR, FTIR, and DSC measurements.

In this study, PLLA with low molecular weights were produced by direct polycondensation of the lactic acid monomer. PLLAs with different molecular weights in the range of 365-2685, were synthesized by changing polymerization time and temperature. The number of average molecular weight of the PLLA increased significantly with increasing polymerization time. This is a general behavior in all polycondensation reactions. The thermal properties of the low molecular weight PLLA were investigated by DSC and poly(L-lactic acid) is a semicrystalline and relatively hard material with glass transition temperature at about 52.05°C. The reaction rate is k = 1.87x10^-4 L/mol.s and k = 1.21x10^-3 L/mol.s for 180 and 200^oC respectively and the activation energy of the reaction is 166 kJ/mol.