SP-PLP-EPR study of chain-length-dependent termination in free-radical polymerization of n-dodecyl methacrylate, cyclohexyl methacrylate, and benzyl methacrylate: evidence of "composite" behavior

The Journal of Physical Chemistry. a
Michael BubackGregory T Russell

Abstract

The chain-length dependence of the termination rate coefficient in n-dodecyl methacrylate (DMA), cyclohexyl methacrylate (CHMA), and benzyl methacrylate (BzMA) bulk free-radical homopolymerizations at ambient pressure and at temperatures from -20 to 0 degrees C is deduced using the recently developed technique of SP-PLP-EPR: pulsed-laser polymerization (PLP) in which time-resolved EPR measurement of radical concentration, cR, is made following each single pulse (SP) of an excimer laser. The decay of cR results from termination of radicals of almost identical size. Their chain length, i, increases linearly with time, t, after applying a SP. The rate coefficient, kt(i,i), for termination of two radicals of size i is determined by fitting the experimental cR vs t data. This process demonstrates that (at least) two power-law exponents are necessary to describe kt(i,i) over the extended chain-length range of i = 1 to 1000. This is consistent with the so-called "composite model" , which uses power-law exponents alpha(S) and alpha(L) to describe termination of radicals either shorter or longer, respectively, than a crossover chain length, ic. The fourth parameter obtained from fitting the SP-PLP-EPR data with this model is kt(1,1), th...Continue Reading

Citations

Nov 2, 2009·Macromolecular Rapid Communications·Johannes Barth, Michael Buback

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