Radical polymerization chain length-dependent changes

Polymeric Radicals and Chain-Length Dependent Changes in ESR Spectra... 

Equation 56 indicates a first-order dependence of the rate of polymerization on the monomer concentration and a square-root dependence on the concentration of the initiator. These dependencies have been confirmed for the example of many polymerizing systems. It should be pointed out that deviations from equation 56 (such as chain-length-dependent rate coefficients or primary radical termination) are manifest in a change in the exponents associated with the initiator and monomer concentrations (386,387). The rate of polymerization will scale with a weaker than square-root dependence on [I] and a stronger than hnear dependence on [M]. Extreme dilution of monomer can also change the exponents of monomer and initiator concentration. Equation 56 is easily integrated to yield an expression which directly correlates the monomer conversion with the observed kinetic rate coefficient obs-... 

Different kinds of approach have recently appeared in a number of important studies, incorporating into the kinetic relations changes in kt with chain length. They start from the empirical functional dependence of the rate constant of bimolecular termination on the degree of polymerization of the reacting radicals... 

He polymerized methacrylonitrile by means of 2,2 -azobisisobutyronitrile. The isobutyronitrile radical generated by initiator decomposition is structurally almost identical with the macroradical end group. Under these conditions, the rate constant of primary radical termination should be very near to the rate constant of termination between oligomeric and polymeric radicals. The studied polymerizations were carried out in dimethylformamide, which is a poor solvent for polymethacrylonitrile. In poor solvents, the change in termination rate with the length of the growing chain should not depend on the excluded volume [10],... 

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