| Abstract
| - In situ 1H nuclear magnetic resonance (NMR) spectroscopy has been used to directlyinvestigate the processes that occur during the early stages (typically the first few monomer additionsteps) of an AIBN-initiated reversible addition−fragmentation chain transfer polymerization of styrenein the presence of the RAFT agent cyanoisopropyl dithiobenzoate at 70 and 84 °C. The change inconcentration of important dithiobenzoate species as a function of time has been investigated. It wasfound that the reaction was extremely selective during the period of consumption of the initial RAFTagent (defined as the initialization period), with almost no production of RAFT-capped chains of degreeof polymerization greater than unity until all of the cyanoisopropyl dithiobenzoate was converted to itssingle monomer adduct. The rate-determining step for this process was found to be the addition(propagation) of the cyanoisopropyl radicals to styrene. During the period where the initial RAFT agentwas consumed, fragmentation of formed intermediate radicals strongly favored the production of thetertiary cyanoisopropyl radicals, which were the only significant propagating species during that period.This led to a greater rate of propagation during that period, since the propagation rate coefficient for thecyanoisopropyl radical is greater than that of polystyryl radicals. It was found that inhibition effects canoccur in the presence of RAFT agents in homogeneous media when the kp for initiator fragments is smallerthan for long chain radicals, which is a result of this aspect of the RAFT mechanism.
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