Modeling free radical polymerization: cyclization and chain transfer reactions

Abstract

In this study, the free radical polymerization of different unsaturated compounds is investigated. In the first part entitled “Cyclopolymerization Reactions of Diallyl Monomers: Exploring Electronic and Steric Effects using DFT Reactivity Indices”, the regioselectivity in the cyclopolymerization of diallyl monomers is investigated using DFT based reactivity indices. The experimentally observed mode of cyclization (exo versus endo) of eleven selected radicals involved in this process is reproduced by the computation of both activation energies, entropies, enthalpies, and Gibb’s free energies for the 5- and 6- membered cyclization reactions. Next, a number of relevant DFT based reactivity indices such as non-spin polarized (f0), spin polarized Fukui functions (fNN0), spin densities ρs, and dual descriptors (f(2)(r)) were applied, in order to probe the role of the polar and stereoelectronic effects in this reaction. The dual descriptor has been found to reproduce best the experimental trends, confirming the important role of the stereo-electronic effects. In the second part of this study entitled “Free Radical Polymerization of Acrylamide”, the polymerization reaction of acrylamide is modeled in the presence of a series of thiophenols which act as chain transfer agents. Polyacrylamide, and copolymers of polyacrylamide have received considerable attention because they have reached large-scale industrial use. The process of chain transfer is used to control mostly the molecular weight, the structure and in some cases the functionality. The propagation rate analysis has showed that most accurate results can be obtained by using M05-2X/6-311++G(3df,2p) method. The correlation between the calculated trend of the chain transfer constants and the experimental results has been reproduced with the MPWB1K/6-311++G(3df,2p) methodology.