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) (k(p)M)(-1), where c is it dimensionless chain-transfer constant, k(p) the propagation rate coefficient and M the monomer concentration an analytical an analytical expression for k(t) 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 k(t) 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 k(t).