| Abstract: | Polyesterification of diacid and diol in the absence of foreign acid is carried out under constant reaction temperatures from 140 to 180°C (rather than under constant oil bath temperature as is usually done) and molar ratios r of diol to diacid from 1 to 3.55. The experimental data obtained cannot fit conventional rate equations as they appear in the literature. Based on ion pair formation and considering additional proton transfer from acid to alcohol, we propose a reaction mechanism and rate equations. The rate equation is found to fit our experimental data very well except for r = 1. At r = 1, the kinetic plot shows two straight lines rather than one as predicted. This is attributed to unremoved water due to the higher molecular weight (and therefore higher viscosity) at r = 1 which causes a reverse reaction and slower apparent reaction rate. |
