Kinetic Trends in RAFT Homopolymerization from Online Monitoring

Automatic continuous online monitoring of polymerization reactions (ACOMP) was used to follow kinetic trends in the reversible addition -fragmentation chain transfer (RAFT) polymerization of butyl acrylate (BA) in butyl acetate, using 2-{((dodecylsulfanyl)carbonothioyl)sulfanyl}propanoic acid (DoPAT) as the RAFT agent and 2,2-azobis(isobutyronitrile) as the initiator (AIBN). The goals were to demonstrate the use of ACOMP for RAFT studies and to examine the trend in conversion and evolution of weight-average molar mass Mw and weight-average intrinsic viscosity ( )w for a series of experiments in which the RAFT agent concentration was decreased over a wide range while all the other reaction conditions were held constant; (DOPAT)/(AIBN) ranged from 0 to 2.4. This allowed monitoring the transition from "living"-like behavior in the "controlled radical polymerization" (CRP) regime, where sufficient RAFT agent was used, to the noncontrolled radical polymerization regime as RAFT agent was progressively reduced to zero. The conversion kinetics were found to be essentially zeroeth order in DoPAT, and deviations from living behavior allowed estimates of radical efficiency. The evolution of Mw vs monomer conversion varied dramatically from near-ideal living behavior at high (DoPAT)/(AIBN) to classical radical polymerization behavior at (DoPAT) ) 0. All but one experiment showed a nonzero Mw at f ) 0, and the conversion behavior of Mw points to transfer and branching side reactions, depending on (DoPAT). ACOMP should prove to be a useful tool both for fundamental RAFT research and process development.