Investigation of the radical polymerization kinetics using DSC and mechanistic or isoconversional methods Dimitris S. Achilias Received: 26 September 2013 / Accepted: 26 December 2013 Ó Akade ´miai Kiado ´, Budapest, Hungary 2014 Abstract In this research, an effort was undertaken to investigate radical polymerization kinetics using experimen- tal data from DSC measurements and mechanistic or isocon- versional models. Polymerization of a polar monomer, namely 2-hydroxyethyl methacrylate in the presence of ben- zoyl peroxide initiator was studied. The variation of the effective activation energy with conversion was directly interpreted in terms of the physical phenomena taking place during the reaction in a microscale. Both isothermal and non- isothermal DSC data were employed and the effect of diffu- sion-controlled phenomena on the reaction kinetics at differ- ent conversion regimes was assessed. Finally, the effect of the presence of nanofiller on polymerization kinetics and the activation energy values were estimated and correlated to physical phenomena taking place during polymerization. Keywords Polymerization kinetics  Isoconversional methods  PHEMA  Nanocomposites  DSC Introduction Free-radical polymerization of vinyl monomers is accompa- nied by a significant heat release (polymerization enthalpy) due to the addition reaction to the monomer’s double bond [1]. Amongst thermochemical methods, the most commonly employed one for measuring polymerization kinetics is dif- ferential scanning calorimetry (DSC) where the output signal is proportional to the rate of heat production. DSC is a very sensitive and precise technique for measuring polymerization rate as a function of either time (isothermal mode) or tem- perature (non-isothermal mode), by monitoring the rate of heat released from the polymerizing sample, which is assumed proportional to the reaction rate. One of the greatest advan- tages of this method is that it provides a direct and continuous measurement of the instantaneous reaction rate rather than conversion. The degree of monomer conversion (in terms of double bonds consumed) is calculated by integrating the area between the DSC curves and the baseline established by extrapolation from the trace produced after complete poly- merization (no change in the heat produced during the reac- tion). This process is inherently more accurate than evaluating rates from the slope of the conversion-time curve. In addition, the final conversion can be calculated, together with the maximum polymerization rate and the time to achieve it. Measurements can be easily carried out in a variety of experimental conditions including reaction temperature, ini- tial initiator concentration and monomer(s) chemical struc- ture. Thus, overall kinetic rate constants and the effective activation energy can be easily estimated. The DSC has been an especially useful tool when applied in studies of the gel effect (auto-acceleration) as well as in crosslinking reactions [2]. Use of DSC for studying the kinetics of the isothermal bulk polymerization of several monomers, including methyl methacrylate (MMA) or curing reactions of epoxy and other resins, has been extensively reported in the literature [1, 3, 4]. In addition, a number of papers have been published on modelling of vinyl monomer polymerization kinetics using detailed mechanistic models [5]. However, the articles dealing with the estimation of polymerization kinetics of vinyl monomers using isoconversional methods are rare. Presented in part in the 41st NATAS Conference, August 4–7, 2013, Bowling Green, KY, USA. D. S. Achilias (&) Laboratory of Organic Chemical Technology, Department of Chemistry, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece e-mail: axilias@chem.auth.gr 123 J Therm Anal Calorim DOI 10.1007/s10973-013-3633-y