Conditions for the Determination of Precise and Accurate Free-Radical Propagation Rate Coefficients from Pulsed-Laser-Made Polymer

Abstract

A revision of the long known mathematical representation of the chain length distribution of polymer resulting from pulsed-laser-initiated free-radical polymerization of Aleksandrov, Genkin, Kitai, Smirnova, and Sokolov revealed that it vividly reflects some very essential characteristics of the underlying kinetics, which have so far been largely overlooked. In particular, with respect to an experimental determination of the propagation rate coefficient k p , it was found that this representation suggests the measurement of the chain lengths at maxima or at low molecular weight side inflection points of pulsed initiation originating structures within chain length distributions of pulsed-laser-made polymer, depending on whether sufficiently high or low concentrations of radicals are being produced per initiating laser pulse, respectively. This suggestion was verified for pulsed laser polymerizations of styrene and methyl methacrylate, at which values of k p (styrene) = 92 L mol -1 s -1 and k p (methyl methacrylate) = 359 L mol -1 s -1 were obtained for a temperature of 25 °C.