Polyesters bearing furan moieties. Part 3. A kinetic study of the transesterification of 2-furoates as a model reaction for the corresponding polycondensations

The kinetics and mechanism of transesterification reactions involving furan ic esters (and aliphatic or aromatic counterparts for the sake of compariso n) have been studied in detail using various catalysts and a wide range of experimental conditions. The purpose of this model investigation is to gath er a thorough understanding of the process which simulates the correspondin g syntheses of furanic polyesters. Whereas the orders in the two reagents w as consistently unity, the order with respect to the catalyst varied from 0 .5 to about unity as a function of increasing temperature and of the struct ure of the promoter used. In the case of Ti(OBu)(4) which was the catalyst most used, this behaviour was attributed to the existence of a monomer/dime r equilibrium of the catalyst molecules in the media selected for this work . The presence of the furan heterocycle produced a partial sequestration of the catalyst, through complexation induced by its dienic character, thus r educing the actual rate of transesterification. The existence of this compl ex was inferred by using unreactive furans as retarding additives and shown by FTIR spectroscopy. (C) 1999 Society of Chemical Industry.