Integrated analysis of low profile unsaturated polyester and vinylester resins cured at low temperatures

Unsaturated polyester and vinylester resins are used in a wide variety of applications. These materials provide high structural stability, increased resistance to solvent and temperature, and improved mechanical stability. Low profile additives have been found highly effective in eliminating the polymerization shrinkage of unsaturated polyester resins in high temperature molding processes such as compression molding of SMC and injection molding of BMC. In recent years, the improvement focuses on the development of low temperature and low-pressure fabrication techniques, such as low temperature/low pressure SMC, RTM, SCRIMP, to significantly reduce the tooling cost. However, poor performance of low profile additives and high residual reactivity in low temperature molding processes unavoidably undermine further applications of unsaturated polyester and vinylester resins. Therefore, there is considerable potential for improving the process through greater technical understanding of reaction and volume shrinkage control mechanism in low temperature cure of unsaturated polyester and vinylester resins.; An integrated analysis is carried out in this study to investigate the reaction kinetics and shrinkage control of unsaturated polyester or vinylester resins with low profile additives cured at low temperatures. A differential scanning calorimeter (DSC), a Fourier transform infrared spectrometer (FTIR), and a rheometrics dynamic analyzer (RDA) are used to study the reaction kinetics and rheological behaviors. A dilatometer is applied to study the volume change. A scanning electron microscopy (SEM) and an optical microscopy are employed to investigate the structure and morphology evolution during curing. The effects of curing agents including initiator, promoter, and comonomer on the low temperature polymerization are investigated. These experiments are designed to provide information regarding the polymerization mechanism and microstructure evolution throughout the free radical polymerization. In addition, this information along with the relation between morphology and properties of crosslinked polymeric materials will be used to optimize polymerization conditions of unsaturated polyester and vinylester resins with desired properties for applications in composite matrix.