Nitroxide-Controlled Free-Radical Copolymerization of Vinyl and Divinyl Monomers. Evaluation of Pendant-Vinyl Reactivity

Abstract

The free-radical copolymerization of styrene (monomer 1) with a small amount (≤3 mol %) of 4,4‘-divinylbiphenyl (monomer 2) was carried out at 125 °C with an oligomeric polystyryl adduct with 2,2,6,6-tetramethylpiperidinyl-1-oxy (PS-TEMPO) as an “initiator”. Owing to the “living” character of the TEMPO-mediated polymerization of styryl monomers, this system is characterized by a slow and simultaneous growth of the primary chains and an essentially constant number of primary chains throughout the course of polymerization. The Cp vs C1 as well as C2 vs C1 curves of this system were approximately describable by the simple polymerization theory based on a random distribution of reactants, giving r1 = 0.38 and rp = 1.0 ± 0.1. Here C1, C2, and Cp are the conversions of monomer 1, monomer 2, and pendant vinyl, respectively, and r1 = k11/k12 and rp = k11/k1p, with k1p, for example, being the rate constant for radical 1 to add to pendant vinyl. This system thus makes a sharp contrast to conventional free-radical systems, where the determination of rp is extremely difficult due to the intramolecular cyclization that can occur to a serious degree even at C1 = 0.