Monomer reactivity ratios have been determined for styrene (r1 = 0.35)–ethyleneglycol dimethacrylate (r2 = 0.65) and styrene (r1 = 0.65)‐m‐divinylbenzene (r2 = 0.60), a tracer technique being used to determine the copolymer composition. The data for these divinyl monomers give intersect plots with three different monomer ratios which determine the reactivity ratios. The usual two‐component copolymerization equation is modified by the use of 2M2 for the M2 term where M2 is the mole percent of the divinyl monomer in the charge. Similar data for p‐divinylbenzene do not locate a unique set of reactivity ratios. It is concluded that the copolymerization behavior of symmetrical divinyl monomers in which the vinyl groups do not interact can be evaluated through use of the two‐component copolymerization equation.
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.
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