Photoinitiated polymerization of a dimethacrylate oligomer: 2. Kinetic studies

The kinetic of photoinitiated polymerization of a dimethacrylate oligomer w as studied by using isothermal photocalorimetry. The reaction was realized with 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as radical photoinit iator. Two kinetic models were applied. First, it was shown that an autocat alytic model can describe this reaction in a satisfying way. The reaction t emperature 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 phenomenolog ical 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 polyme rization is taken into account. In addition, by means of a mechanistic mode l, the k, and k, rate constants were calculated. Their evolution with conve rsion was studied at 50 degrees C and well illustrates the importance of th e reactive diffusion mechanism. (C) 1998 Elsevier Science Ltd. All rights r eserved.