Synthesis of hydroxyl‐terminated poly(lactic acid) via polycondensation: An equation to predict molecular weight based on the reaction parameters

Abstract

AbstractLow‐molecular‐weight hydroxyl‐terminated poly(lactic acid)s (PLA‐OHs) were synthesized via the condensation polymerization of L‐lactic acid (LA) with stannous octoate [Sn(Oct)2] as a catalyst along with a small amount of 1,4‐butanediol (1,4‐BDO). The effect of three reaction parameters (i.e., reaction time, catalyst concentration, 1,4‐BDO concentration) on the molecular weight (MW) and molecular weight distribution (MWD) of the PLA‐OHs were investigated with response surface methodology. Three levels for each parameter were selected: 6, 8, and 10 h for reaction time, 0.05, 0.10, and 0.15 mol % catalyst concentrations based on LA content, and 2, 3, and 4 mol % 1,4‐BDO concentrations based on LA content. The physicochemical structures of the polymers were investigated by Fourier transform infrared spectroscopy. The MW and MWD values of the synthesized polymers were investigated by 1H‐NMR and gel permeation chromatography. The results show that when the reaction time was increased, the MW of the PLA‐OHs increased reasonably. The MW of polymers also increased with decreasing amount of catalyst. Increasing the amount of 1,4‐BDO resulted in a decrease in the MW of the prepolymers. The only exception was observed when the lowest reaction time (6 h) was chosen along with a high concentration of 1,4‐BDO; in this case, increasing the catalyst amount resulted in an increase in MW. Also, when we chose a reaction time of 10 h, a catalyst concentration of 0.10 mol % based on LA content, and a 1,4‐BDO amount of 2 mol % based on LA content, we observed the highest MW among the other samples. Finally, an equation was developed by MINITAB software to predict the MWs of the PLA‐OHs on the basis of the reaction parameters. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012