Dithioester-mediated RAFT Polymerization: A Kinetic Study by Mathematical Modelling

Although reversible addition-fragmentation chain transfer (RAFT) polymerizationhas attracted great attention of many researchers over recent years,outstanding questions on the mechanism and kinetics of dithioester-mediatedRAFT polymerization (especially dithiobenzoates) still have remained unsolved. In thiswork, based on experimental observations and exact theoretical predictions, thekinetic schemes of RAFT polymerization are extended to a wider range of reactionssuch as irreversible intermediate radical terminations and reversible transfer reactions.The reactions which have been labeled as kinetic schemes are theoretically the mostprobable existing reactions and are used for mathematical modelling. The detailedkinetic scheme is applied to three kinds of RAFT polymerization systems by utilizing themethod of moments. Unknown kinetic rate constants are obtained by curve fitting of themodelling results and theoretical data, and applying the least square method; orestimation by considering the theoretical facts and experimental findings. The origin ofthe rate retardation and induction periods has been understood by studying the mainand pre-equilibrium stages of dithiobenzoate-mediated RAFT homopolymerization. Acopolymerization system in the presence of RAFT agent has also been examined toconfirm the capability of introduced kinetic scheme in different monomer/RAFT agentsystems. Although unknown parameters were obtained theoretically, their consistencywith other researcher's works shows the accuracy of the modelling procedure. Themodelling results are in excellent agreement with experimental data which proves thevalidity and applicability of the detailed kinetic scheme. The results have shown thatsome reactions may not occur in many RAFT polymerization systems and can beeliminated and therefore more kinetic and mechanistic studies are required.