Premium
The kinetics of free radical polymerizing systems at low conversion, 2 . On the influence of the monomer and initiator concentrations
Author(s) -
Russell Gregory T.
Publication year - 1995
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/mats.1995.040040309
Subject(s) - polymerization , monomer , chemistry , chain termination , kinetic chain length , thermodynamics , chain transfer , chain (unit) , radical polymerization , kinetics , polymer chemistry , bulk polymerization , polymer , physics , quantum mechanics , organic chemistry
In this paper are calculated variations of steady state rates of polymerization R pol with initiator concentration [I] and monomer concentration [M]. For these calculations a chain length dependent termination model which provides a microscopic description of zero conversion bulk and solution polymerization of styrene at 20°C is used. Despite the calculations being necessarily specific in this respect, the principles that are uncovered are general, and so are germane for polymerization of all monomers at all conversions. The central such principle is that any chain length dependence of termination rate coefficients may alone be expected, in the first instance, to induce non‐classical polymerization behavior; specifically, R pol will scale with a weaker than square root dependence on [I] and a stronger than linear dependence on [M]. Further, while the extent of deviation from classical behavior does depend on the severity of the chain length dependence of termination rate coefficients, it does not depend on whether a Smoluchowski or geometric mean model of termination is operative, a finding which counsels reappraisal of some commonly held perceptions regarding low conversion termination. It is also shown that regardless of the chain length dependence of the termination rate coefficient, the occurrence of chain transfer to monomer will act to promote classical polymerization behavior, and it is argued that this has been a factor in many low conversion experimental investigations appearing to have found an at most rather weak chain length dependence of termination; it is further argued that existing experimental data for the variation of R pol with [I] and [M] is not inconsistent with termination being center‐of‐mass diffusion controlled at low conversions. Close attention is paid to experimental data throughout this paper, which concludes by discussing aspects of experimental design, this in the hope that simple measurements of steady state R pol might be more profitably used to elucidate the complexities of free radical polymerization kinetics.