Photopolymerization of bis-aromatic and alicyclic based solid urethane acrylate macromonomer in the presence of large excess of reactive diluent Kinetics and modeling R. Harikrishna • S. Ponrathnam • C. R. Rajan • S. S. Tambe Received: 11 May 2012 / Accepted: 16 July 2012 / Published online: 8 September 2012 Ó Akade ´miai Kiado ´, Budapest, Hungary 2012 Abstract A solid urethane acrylate macromonomer with bis-aromatic as well as alicyclic moieties was synthesized and the kinetics of photopolymerization reactions were studied in the presence of varying concentration of photoinitiator and large excess of reactive diluent using photo DSC. The studies show that the rate of maximum polymerization was found to increase with increase in concentration of photoinitiator while a decrease was observed by an increase in temperature. The final conver- sion showed a decrease at highest isothermal condition due to vitrification. Estimation of kinetic parameters including applicability of autocatalytic and modified autocatalytic models were investigated by nonlinear regression. It was observed that the modified models gave a better fit with the experimental data and kinetic parameters showed a decrease with increase in temperature and an increase with increase in concentration of photoinitiator. Keywords Photopolymerization  Kinetics  Autocatalytic model  Levenberg–Marquardt method Introduction Photopolymerization involves light-induced polymeriza- tion of photopolymerizable monomers/oligomers in the presence of photoinitiators. Lab-scale optimization study of photopolymerization can be carried out using real time FTIR spectroscopy or photo DSC [1, 2]. The process involves an instantaneous transformation of a liquid resin into a solidified material. Many additives can be added to the formulation depending on the final physical require- ments of the cured material. The entire process involves initiation, propagation, and termination processes. The kinetics is mostly controlled by diffusion controlled pro- cesses and is mostly arrested when vitrification/cross- linking prevents the systems from undergoing further conversion [3]. Due to its complex nature, the course of photopolymerization reaction is influenced by the nature of monomer/oligomer, photoinitiator and added additives such as reactive diluent, coinitiator, and stabilizer [4]. The physical parameters which affect the cure include analysis temperature, gaseous environment, intensity, and wave- length of irradiation [5]. Photopolymerization is an in situ process and is heavily influenced by viscosity assisted reaction diffusion in addition to other modes of diffusions such as translational and segmental diffusions [2]. The heat-flow profile shows ascending and descending nature due to autoacceleration or an enhanced chemical conver- sion arising from initial volume relaxation and autodecel- eration or reduced chemical reaction resulting from final volume shrinkage. The lab-scale optimized compositions can be used for performance evaluation in various surface coating applications. This study deals with the effect of above discussed parameters on the photopolymerization kinetics of a solid macromonomer in the presence of large excess of reactive diluent. Kinetic studies and modeling of photopolymerization processes have been successfully done by many researchers [2, 6–9]. Generalized autocatalytic kinetic model as pro- posed by Kamal for thermal cure studies is given by the expression R. Harikrishna (&)  S. Ponrathnam  C. R. Rajan Division of Polymer Science and Engineering, National Chemical Laboratory, Pune 411008, India e-mail: r.harikrishna@ncl.res.in S. S. Tambe Division of Chemical Engineering and Process Development, National Chemical Laboratory, Pune 411008, India 123 J Therm Anal Calorim (2013) 112:805–813 DOI 10.1007/s10973-012-2619-5