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Dependence of termination kinetics in methyl acrylate–dodecyl acrylate free‐radical copolymerization on comonomer composition, pressure, temperature and conversion
Author(s) -
Buback Michael,
BarnerKowollik Christopher,
Kuelpmann Albrecht
Publication year - 2002
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/1521-3935(200209)203:13<1887::aid-macp1887>3.0.co;2-2
Subject(s) - monomer , chemistry , methyl acrylate , polymer chemistry , acrylate , diffusion , copolymer , steric effects , reaction rate constant , polymerization , kinetics , analytical chemistry (journal) , thermodynamics , polymer , stereochemistry , organic chemistry , physics , quantum mechanics
The termination kinetics of the free‐radical bulk copolymerization of dodecyl acrylate (DA) and methyl acrylate (MA) has been investigated at various monomer mole fractions between 15 and 50 °C and up to 2000 bar. The ratio of termination to propagation rate coefficients, ( k t / k p ) copo , is measured via the single pulse‐pulsed laser polymerization (SP‐PLP) technique. Chain‐length averaged k t,copo are deduced from ( k t / k p ) copo in conjunction with k p,copo data that are estimated via a simplified version of the implicit penultimate unit effect (IPUE) model. At low and moderate degrees of monomer conversion extended ranges of almost constant k t are observed where termination is controlled by segmental diffusion with important contributions of steric effects. These plateau k t values are significantly – by almost two orders of magnitude – different for MA and DA. The increase with MA content of k t,copo is adequately described by a penultimate unit model which uses the geometric mean approximation for estimating rate coefficients of cross‐termination between radicals of different free‐radical terminus. The model applies within the entire pressure and temperature range of the present study. At high degrees of monomer conversion, at and above 50%, homo‐ k t and k t,copo are almost insensitive toward the composition of the monomer mixture. The termination rate under these conditions is essentially controlled by reaction diffusion.Relative monomer conversion, c M ( t )/ c M,0 , vs. time, t , plot of a methyl acrylate (MA) – dodecyl acrylate (DA) copolymerization ( f MA,0 = 0.5) induced by a single laser pulse at 30 °C and 10 bar. The difference between measured and fitted (to Equation (4)) data is illustrated by the plot of residuals ( res ) in the lower part of the figure.