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 (less than or equal to 3 mol %) of 4,4'-divinylbiphenyl (monomer 2) was carried out at 125 degrees 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.