Study of the isothermal bulk polymerization of methyl methacrylate by differential scanning calorimetry

Course and kinetics of the isothermal bulk polymerization of methyl methacrylate were studied by differential scanning calorimetry. The initiator used was 2,2′‐azoisobutyronitrile. The polymerization was investigated at temperatures between 70 and 90°C at constant initiator concentration, 5,2.10−2 mol dm−3. The heat of polymerization at 70°C is −52,3 kJ/mol (−12,5 kcal/mol) and decreases, i.e. becomes more negative, with increasing temperature. Initial rate constants for the polymerization were also determined and from them the overall activation energy, 77 kJ/mol (18,4 kcal/mol), which is in good agreement with the literature value. Another series of polymerization experiments were performed at 80°C with variable amounts of the initiator. The heat of polymerization found is −52,8 kJ/mol (−12,6 kcal/mol) and depends only slightly on the initiator concentration. The overall rate of polymerization at low degrees of conversion depends on the square root of the initiator concentration. These findings thus corroborate the conclusion reached by other authors that differential scanning calorimetry is a useful method for studying the kinetics of polymerization.