Rate coefficients as a function of time during the after-effect of a photoinduced crosslinking polymerization
Polimery 2002, No 10, 734
The polymerization of a dimethacrylate monomer occurring in the dark after the initiating light has been switched off (so-called after-effect) was modeled by assuming of two diHerent termination mechanisms: monomolecular (ModelI) and bimolecular (Model 2). Time dependent monomolecular termination (ktm) and bimolecular termination (ktb) rate coefficients and a time independent propagation rate coefficient kpare used in the models. Both ktm and ktb are polynomial functions of time. A very important feature of the newly developed models is that free terms of polynomials correspond to values of ktm (Model 1) or kp[P˙]0 (Model 2) at the moment of stopping the irradiation (tdark = 0; [P˙]0 constitute macroradical concentrations at tdark = 0). Those values can be considered as deseribing the process during continuous irradiation. Calculations were performed for eight photoinduced polymerization processes, in which initiation had be en interrupted at various degrees of double bond conversions (denoted as starting conversions). It was found that the conversion dependence of ktb [P˙]0 and ktm, parameters extrapolated to tdark = 0 appearing in two various termination models was similar.
Keywords: photopolymerization, after-effect, (tetraethylene glycol) dimethacrylate, modeling, termination mechanism, time-dependent rate coefficients