Tracer techniques for the determination of monomer reactivity ratios. I. A direct counting technique applied to the styrene–methacrylate copolymerization

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Abstract
A direct counting technique has been evaluated and used for the determination of monomer reactivity ratios. Windowless gas‐flow counting of polymer samples plated directly on planchets gave reproducible counting rates and nearly linear self‐absorption curves in the 8–25 mg./planchet range. Copolymer composition data obtained by radioactivity assay on a series of styrene C14/methyl methacrylate copolymers gave monomer reactivity ratios of r1 = 0.48, r2 = 0.46 at 60° and r1 = 0.60, r2 = 0.55 at 132°; these values are in good agreement with previously recorded values.