Pursuit of Reinitiation Efficiency of Resonance-Stabilized Monomeric Allyl Radical Generated via Degradative Monomer Chain Transfer in Allyl Polymerization

For a deeper understanding of allyl polymerization mechanism, the reinitiation efficiency of resonance-stabilized monomeric allyl radical was pursued because in allyl polymerization it is commonly conceived that the monomeric allyl radical generated via the allylic hydrogen abstraction of growing polymer radical from monomer, i.e., degradative monomer chain transfer, has much less tendency to initiate a new polymer chain and, therefore, this monomer chain transfer is essentially a termination reaction. Based on the renewed allyl polymerization mechanism in our preceding article, the monomer chain transfer constant in the polymerization of allyl benzoate was estimated to be 2.7 x 10(-2) at 80 degrees C under the polymerization condition, where the coupling termination reaction of growing polymer radical with allyl radical was negligible and, concurrently, the reinitiation reaction of allyl radical was enhanced significantly. The reinitiation efficiencies of monomeric allyl radical were pursued by the dead-end polymerizations of allyl benzoate at 80, 105, and 130 degrees C using a small amount of initiators; they increased remarkably with raised temperature. Thus, the enhanced reinitiation reactivity of allyl radical at an elevated temperature could bias the well-known degradative monomer chain transfer characteristic of allyl polymerization toward the chain transfer in common vinyl polymerization. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 156-163, 2011