The kinetic of photoinitiated polymerization of a dimethacrylate oligomer was studied by using isothermal photocalorimetry. The reaction was realized with 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as radical photoinitiator. Two kinetic models were applied. First, it was shown that an autocatalytic model can describe this reaction in a satisfying way. The reaction temperature does not influence the m and n orders of the reaction which were found to be constant and respectively equal to 0.8 and 2. The phenomenological rate constant k varies with temperature according to the Arrhenius law up to 80 degrees C. Above this temperature, this law can again be checked if the initial variation of double bond concentration due to thermal polymerization is taken into account. In addition, by means of a mechanistic model, the k, and k, rate constants were calculated. Their evolution with conversion was studied at 50 degrees C and well illustrates the importance of the reactive diffusion mechanism.