Modeling Termination Kinetics of Non-Stationary Free-Radical Polymerizations

Abstract

Pulsed-laser induced polymerization is modeled via an approach presented in a previous paper.[1] An equation for the time dependence of free-radical concentration is derived. It is shown that the termination rate coefficient may vary significantly as a function of time after applying the laser pulse despite of the fact that the change in monomer concentration during one experiment is negligible. For the limiting case of t ≫ c–1 (kpM)–1, where c is a dimensionless chain-transfer constant, kp the propagation rate coefficient and M the monomer concentration, an analytical expression for kt is derived. It is also shown that time-resolved single pulse-laser polymerization (SP–PLP) experiments can yield the parameters that allow the modeling of kt in quasi-stationary polymerization. The influence of inhibitors is also considered. The conditions are analyzed under which M (t) curves recorded at different extents of laser-induced photo-initiator decomposition intersect. It is shown that such type of behavior is associated with a chain-length dependence of kt.