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The influence of styrene content on styrene added vinylester resin (VER) is investigated. The network structure and its thermal properties is investigated by differential scanning calorimetry (DSC) and the combination of thermal gravimetric analysis (TGA) and Fourier transform infrared spectrometry (FTIR) (TGA-FTIR). The glass transition temperatures ( Tgs) of the resins are found to decrease systematically with increasing styrene content, which decreases the crosslink density of the cured materials. The Tg of VER samples cured 97-98% is significantly lower, by as much as 25°C, than the Tg of a fully cured (100%) sample. This is due to the plasticizing effect of unreacted styrene in the network. The combination of TGA and FTIR confirm the evolution of gaseous styrene moieties at the degradation temperature of vinylester groups, the relative amount of styrene emitted being higher with increasing styrene content. A good correlation is found between the thermal properties by DSC and the results obtained from the TGA-FTIR system.

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