Kinetics of the preparation of rubber seed oil alkyds

The kinetics of the polyesterification of glycerol, phthalic anhydride and rubber seed oil leading to the formation of alkyd resins were studied at temperatures between 230 and 250°C. Six samples of the resin having oil contents of 20% (I), 30% (II), 35% (III), 40% (IV), 50% (V) and 60% (VI) were prepared. The extent of reaction was monitored by determining the acid value of aliquots of the reaction mixture at various intervals of time and by measuring the volume of water evolved. The extent of reaction (PA) and average degree of polymerization (DP) were calculated from end group analysis of aliquots of the reaction mixture withdrawn at various intervals of time. The initial reaction rates followed second order kinetics and thereafter deviations were observed. The average degree of polymerization calculated in the region of deviation from second order kinetics suggests the occurrence of chain branching at relatively short intervals along the polymer chain. The second order rate constants were found to be of the order of 10-5 g (mg KOH)-1 min-1. Copyright © 1996 Elsevier Science Ltd.