Synthesis of organosiloxane copolymers using enzymatic polyesterification

Lipase B from Candida antarctica was used to catalyze the condensation polymerization of 1,3-bis(3-carboxypropyl)tetramethyldisiloxane with three different alkanediols (1,4-butanediol, 1,6-hexanediol and 1,8-octanediol) in the bulk and under reduced pressure. The effect of temperature, vacuum, enzyme activity and enzyme concentration on the reaction kinetics was investigated. Progress of the reactions was monitored using Fourier Transform Infrared Spectroscopy (FTIR) and Gel Permeation Chromatography (GPC) by analyzing the samples collected at selected time intervals. In all the three polyesterification reactions that were investigated herein, the rate of product formation increased when the temperature was increased from 50 to 90 °C. An increase in the applied vacuum from 50 to 300 mm Hg (vacuum gauge pressure) was found to have little or no effect on the rate of product formation during the first stage of the reaction (24 h). However, the molecular weight of the polymer increased during the latter half of the reaction, apparently due to a shift from reaction control to diffusion control in the increasingly viscous system. The activity of the enzyme and chain-length of the alkanediols were found to be critical for the reactions investigated. Furthermore, the activity of the recovered lipase using THF and toluene was reduced to below 50%, apparently due to the enzyme leaching out from the immobilized acrylic resin.