Curing reaction of saturated aliphatic polyester modified unsaturated polyester resins

Two series of unsaturated polyesters (UPE from isophthalic acid, fumaric acid, and propylene glycol) were prepared. In series‐A resins, UPEs wee thickened with isocyanate‐terminated saturated aliphatic polyestes, i.e., an isocyanate‐terminated polycaprolactone diol (PE‐di‐OL), through reaction of the isocyanate group with the hydroxyl group of the UPE. In series‐B resins, the UPEs were mixed with saturated aliphatic polyesters i.e., PE‐di‐OL. The curing reaction of these two series of UPEs with styrene was studied by using differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The DSC data show that for a fixed PE‐di‐OL molecular weight, the curing reaction rate of series‐A UPE is faster than that of series‐B UPE. The variation of microgel size during curing ws studied by GPC. These results revealed that microgel formation has a great effect on the kinetics of cure for the unsaturated polyester‐styrene system. The curing of these two series of UPEs is found to strongly depend on the compatibility of the components in the curing system.