Computational Study of Chain Transfer to Monomer Reactions in High-Temperature Polymerization of Alkyl Acrylates

Abstract

This article presents a computational study of chain transfer to monomer (CTM) reactions in self-initiated high-temperature homopolymerization of alkyl acrylates (methyl, ethyl, and n-butyl acrylate). Several mechanisms of CTM are studied. The effects of the length of live polymer chains and the type of monoradical that initiated the live polymer chains on the energy barriers and rate constants of the involved reaction steps are investigated theoretically. All calculations are carried out using density functional theory. Three types of hybrid functionals (B3LYP, X3LYP, and M06-2X) and four basis sets (6-31G(d), 6-31G(d,p), 6-311G(d), and 6-311G(d,p)) are applied to predict the molecular geometries of the reactants, products and transition sates, and energy barriers. Transition state theory is used to estimate rate constants. The results indicate that abstraction of a hydrogen atom (by live polymer chains) from the methyl group in methyl acrylate, the methylene group in ethyl acrylate, and methylene groups in n-butyl acrylate are the most likely mechanisms of CTM. Also, the rate constants of CTM reactions calculated using M06-2X are in good agreement with those estimated from polymer sample measurements using macroscopic mechanistic models. The rate constant values do not change significantly with the length of live polymer chains. Abstraction of a hydrogen atom by a tertiary radical has a higher energy barrier than abstraction by a secondary radical, which agrees with experimental findings. The calculated and experimental NMR spectra of dead polymer chains produced by CTM reactions are comparable. This theoretical/computational study reveals that CTM occurs most likely via hydrogen abstraction by live polymer chains from the methyl group of methyl acrylate and methylene group(s) of ethyl (n-butyl) acrylate.

On the Use of Quantum Chemistry for the Determination of Propagation, Copolymerization, and Secondary Reaction Kinetics in Free Radical Polymerization

“…Intermolecular hydrogen abstractions like chain transfer to monomer and chain transfer to polymer were studied in various systems [106,[137][138][139][140][141]. Intramolecular hydrogen abstractions were investigated as well, focusing on the backbiting reactions that occur when a chain-end radical (CER) abstracts a hydrogen from its own backbone, forming a mid-chain radical (MCR) [70,106,[141][142][143][144].…”

Nanoparticles of 4,7‐dichloro‐2‐quinolinemethylacrylate‐based copolymers and their potential cytotoxic activity on human breast carcinoma cells

“…Another possible factor that influenced in the decrease of M w (or M n ) of the copolymers as AQM molar fraction increases was the fact that AQM monomer has labile hydrogens atoms (methylene group between the quinoline moiety and the ester group, and α‐vinylic hydrogen) that can be easily abstracted by their growing polymeric radicals during its copolymerization with VP, promoting premature termination of the polymer chains and consequently copolymers with lower molecular weights are obtained. This “chain transfer to monomer” mechanism is suggested in previous studies on polymerization of benzylacrylate monomer which has similar functional groups as the AQM monomer (i.e., CH 2 = CHCOOCH 2 ‐aromatic system). Note that copolymers have an unimodal molecular weight distribution, as indicated by the GPC chromatograms in Figure S1 (see Supporting Information).…”

A Theoretical and Experimental Study for Screening Inhibitors for Styrene Polymerization

“…Therefore, the main drawback of utilizing antioxidants or antipolymersis that they are not individually capable of inhibiting both routes of UP formation. To address the mentioned issue, the utilization of antipolymer/antioxidant blends has been proposed as the state of the art currently [31][32][33]. This strategy would result in the simultaneous inhibition of three UP routes.…”