The radical crosslinking of ortho diallyl phthalate was studied with dynamic mechanical analysis and infrared spectroscopy, the combination of which provides an in situ method for the elucidation of the effects of the reaction temperature. Studies of the side reactions (degradative transfer) showed that the reaction temperature must be lower than 170 degrees C to obtain the optimal mechanical properties when dicumyl peroxide is used as a initiator. Above 170 degrees C, at the end of polymerization, the extent of reaction increases with the reaction temperature, whereas the crosslinking density decreases. These phenomena can be explained by an intramolecular cyclization reaction which consumes the allyl bond without formation of a crosslinking point. Furthermore, the gel point behavior was well characterized from the divergence of zero shear rate viscosity and the power law in dynamic moduli. The value of the relaxation exponent (Delta = 0.75) was found to be close to the theoretical percolation t value. However, the exponent increases slightly with the reaction temperature, suggesting a more open network structure. This phenomenon was also explained by an intramolecular reaction that evolves as a function of temperature.