A THEORETICAL DESCRIPTION OF A METHOD FOR MODEL-INDEPENDENT DETERMINATION OF BIMOLECULAR CHAIN-LENGTH-DEPENDENT FREE-RADICAL-TERMINATION RATE COEFFICIENTS

A theoretical description is given of a method for model-independent d etermination of bimolecular chain-length-dependent free-radical-termin ation rate coefficients. By on-line determination of the monomer conce ntration versus time in a time-resolved pulsed laser polymerization, t he value of the termination rate coefficient k(t)(i,i) of the terminat ion reaction between species of identical chain length can be determin ed in a very simple fashion. The key assumption in this ht determinati on is that the radical chain-length distribution that is generated wit h a laser pulse is extremely narrow, such that all chains can be consi dered as being identical in chain length. With computer simulations th e effects of several processes which could undermine this key assumpti on were investigated. For the monomer methyl methacrylate (MMA) the ef fects of(i) a Poisson distribution of the polymerization events, (ii) chain transfer to monomer, and (iii) the presence of a background init iation process were investigated. For MMA, none of these processes int erfere with the model-independent determination of the termination rat e coefficients, as long as suitable experimental conditions are chosen , which follow from the simulations.