Effects of chemical structure of polyurethane-based low-profile additives on the miscibility, curing behavior, volume shrinkage, glass transition temperatures, and mechanical properties for styrene/unsaturated polyester/low-profile additive ternary systems. I: Miscibility, curing behavior, and volume shrinkage

The effects of chemical structure and molecular weight of three series of t hermoplastic polyurethane-based (PU) low-profile additives (LPA) on the mis cibility of styrene (ST)/unsaturated polyester (UP) resin/LPA ternary syste ms prior to reaction were investigated by using the Flory-Huggins theory an d group contribution methods. The reaction kinetics during the cure at 110 degrees C and the cured sample morphology were also studied by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respect ively. The phase-separation characteristics of ST/UP/LPA systems during the cure, as revealed by the cured-sample morphology, and the DSC reaction-rat e profile, could be generally predicted by the calculated upper critical so lution temperature for the uncured ST/UP/LPA systems. Finally, based on the measurements for volume change and microvoid formation, volume shrinkage c haracteristics for the cured ST/UP/LPA systems have been explored. (C) 2000 John Wiley & Sons, Inc.