Kinetic analysis of the RAFT copolymerization of styrene and maleic anhydride by differential scanning calorimetry

A kinetic study of the copolymerization of styrene (S) and maleic anhydride (MA) in the presence of dibenzyl trithiocarbonate (DBTTC) as RAFT agent monitored by differential scanning calorimetry, is presented. The results obtained indicate that the polymerization proceeded in a controlled manner. The average activation energy (E) of the copolymerization obtained by Ozawa and Kissinger methods (62 ± 2 kJ mol−1) showed good agreement with the E value obtained by the isothermal method (67 ± 2 kJ mol−1). These values agree well with the value of 65 kJ mol−1 reported for the nitroxide-mediated copolymerization of S and MA. Calculations using isoconversional methods show that Ea is not constant within the whole conversion range. As the reaction proceeds and higher conversions are reached, Ea decreases to lower values due to diffusion-controlled effects. A first-order reaction model is applied to determine overall kinetic rate constants at different temperatures and different MA molar feed fractions. Polymerization rate increased approximately four orders of magnitude when temperature changed from 90 °C to 110 °C. Polymerization rate is also strongly affected by MA content. It increased by a factor of about three when MA changed from 30% to 50% molar content in the copolymer.