Radical Polymerization - Reactivity

Reactivity

Traditionally, the reactivity of monomers and radicals are assessed by the means of copolymerization data. Q-e scheme, the most widely used tools for the semiquantitative prediction of monomer reactivity ratios, was first proposed by Alfrey and Price in 1940s. The scheme takes into account the intrinsic thermodynamic stability and polar effects in the transition state. A given radical and a monomer is considered to have an intrinsic reactivity of Q₁ and Q₂, respectively. The polar effects in the transition state, the supposed permanent electric charge carried by that entity (radical or molecule), is quantified by the factor e, which is a constant for a given monomer, and has the same value for the radical derived from that specific monomer. For reaction between a radical (species 1) and a monomer (species 2), the rate constant, k₁₂, was postulated to be related to the four relevant reactivity parameters by

The monomer reactivity ratios for the copolymerization of monomers 1 and 2 can be given by