CURING OF UNSATURATED POLYESTER RESINS - EFFECTS OF COMONOMER COMPOSITION .2. HIGH-TEMPERATURE REACTIONS

The effects of comonomer composition on the curing kinetics of unsaturated polyester (UP) resins at 100-120-degrees-C were investigated by differential scanning calorimetry (DSC) and infrared spectroscopy (IR) over the entire conversion range. One Commercial UP resin, UP2821, with 6.82 unsaturated C = C bonds per polyester molecule, was used. For styrene/UP2821 reactions, experimental results of the initial and maximum reaction rates by DSC at 100-120-degrees-C revealed that the styrene content, as well as the reaction temperature, would affect the formation of microgel structures. As the initial molar ratio of styrene to polyester C = C bonds increased, the styrene swelling effect could enhance the intramicrogel cross-linking reactions, while the styrene dilution effect could diminish the intermicrogel cross-linking reactions. The competition between the two reactions would depend on the reaction temperatures. Finally, a microgel-based reaction mechanism was proposed for the high temperature reactions.