An Ab initio investigation of the chain-length dependence of the addition-Fragmentation equilibria in RAFT polymerization

Ching Yeh Lin, Michelle L. Coote

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13 Citations (Scopus)

Abstract

Ab initio molecular orbital theory has been used to study and explain the effects of chain length on the additionfragmentation equilibrium constant in reversible additionfragmentation chain transfer (RAFT) polymerization. New data is presented for azobisisobutyronitrile-initiated t-butyl dithiobenzoate- mediated polymerization of methyl methacrylate, and 2-(((ethylthio) carbonothioyl)thio)propanoic acid-mediated polymerization of acrylamide, and compared with published results for a dithiobenzoate-mediated polymerization of styrene and a trithiocarbonate-mediated polymerization of methyl acrylate. The effects of primary and penultimate substituents on the additionfragmentation equilibrium constants in RAFT polymerization can be very large (up to eight orders and four orders of magnitude respectively) and should be taken into account in kinetic models. Antepenultimate unit effects are relatively small, implying that, for most systems, chain length effects have largely converged by the dimer stage. However, for sterically bulky monomers capable of undergoing anchimeric interactions such as hydrogen bonding, the onset and convergence of these substituent effects is delayed to slightly longer chain lengths. The magnitude and direction of chain-length effects in the additionfragmentation equilibrium constants varies considerably with the nature of the RAFT agent, the initiating species, the propagating radical, and the solvent. The observed substituent effects arise primarily in the differing stabilities of the attacking radicals, but are further modified by homoanomeric effects and, where possible, hydrogen-bonding interactions.

Original languageEnglish
Pages (from-to)747-756
Number of pages10
JournalAustralian Journal of Chemistry
Volume64
Issue number6
DOIs
Publication statusPublished - 2011
Externally publishedYes

Bibliographical note

Funding Information:
M.L.C. gratefully acknowledges useful discussions with Professor Leo Radom and receipt of an Australian Research Council (ARC) Future Fellowship, financial support from the ARC under their Centres of Excellence program and the generous allocation of computing time on the National Facility of the National Computational Infrastructure.

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