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

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 C p vs C 1 as well as C 2 vs C 1 curves of this system were approximately describable by the simple polymerization theory based on a random distribution of reactants, giving r 1 = 0.38 and r p = 1.0 ± 0.1. Here C 1, C 2, and C p are the conversions of monomer 1, monomer 2, and pendant vinyl, respectively, and r 1 = k 11 / k 12 and r p = k 11 / k 1p, with k 1p, 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 r p is extremely difficult due to the intramolecular cyclization that can occur to a serious degree even at C 1 = 0.