Wednesday, July 13, 2011

Monomer Reactivity Ratio

The monomer reactivity ratio, r, are the ratio of the rate constant for a radical adding its own monomer to the rate constant for its adding the other monomer. If the r > 1 means the radical M1 prefer to add M2, r < 1 means that it prefers to add M2. In the system styrene (M1) as monomer 1-methyl methacrylate (M2), for example, r1 = 0.52 and r2 = 0.46; each radical adds the other monomer about twice as first its own.

Since the rate constant for initiation and termination do not appear, the composition of the copolymer is independent of overall reaction rate and initiator concentration. The reactivity ratios are unaffected in most cases by the presence of inhibitors, chain transfer agents, or solvents. Even in heterogeneous system they remain unchanged, unless the availability of the monomers is altered by their distribution between phases. A change from a free radical to an ionic mechanism, extensive compilation is given by Young (1975s).

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