New thermally stable photoreactive prepolymers were synthesized by the reaction of t-cinnamic acids (CAs) with different functional groups and two kinds of epoxy resins which are a biphenyl type epoxy resin and a novolac type epoxy resin with furan ring. Their photocure reaction rates and the extent of reaction conversion were measured with Fourier transform infrared spectroscopy, and their photocure reactions were analyzed in terms of nth-order kinetic reaction equation. Their optical and thermal stability were investigated with UV-Visible spectroscopy and thermogravimetric analysis (TGA). Their photocure reaction rates and the extent of reaction conversion increased with the intensity of UV irradiation. The photoreactive cinnamate prepolymers synthesized from FPREP epoxy resin showed a lower reaction conversion rate and a reaction constant than those of the photopolymer systems based on EBPXA epoxy resin. The reaction conversion rates of these photopolymers with hydroxyl group as a functional group of cinnamate were lower than those of only cinnamate moiety. Thermal stability was studied by observing changes in the transmittance of the photocured polymer films upon heating and by measuring weight loss with temperature using TGA. These photoreactive prepolymers with a biphenyl group showed good thermal properties, with almost no transmittance change in the visible range even after they were heated at 250 degrees C for 1 hour, and these cinnamate photopolymer systems exhibited little weight loss up to about 300 degrees C.