First-principles prediction and interpretation of propagation and transfer rate coefficients

Heuts, Johan P. A., Sudarko and Gilbert, Robert G. (1996). First-principles prediction and interpretation of propagation and transfer rate coefficients. In: 2nd International Symposium on Free Radical Polymerization - Kinetics and Mechanisms. 2nd International Symposium on Free Radical Polymerization - Kinetics and Mechanisms, Genoa, Italy, (147-157). 26-31 May 1996. doi:10.1002/masy.19961110115


Author Heuts, Johan P. A.
Sudarko
Gilbert, Robert G.
Title of paper First-principles prediction and interpretation of propagation and transfer rate coefficients
Conference name 2nd International Symposium on Free Radical Polymerization - Kinetics and Mechanisms
Conference location Genoa, Italy
Conference dates 26-31 May 1996
Proceedings title 2nd International Symposium on Free Radical Polymerization - Kinetics and Mechanisms   Check publisher's open access policy
Journal name Macromolecular Symposia   Check publisher's open access policy
Place of Publication Weinheim, Germany
Publisher Wiley - V C H Verlag GmbH
Publication Year 1996
Sub-type Fully published paper
DOI 10.1002/masy.19961110115
ISSN 1022-1360
1521-3900
Volume 111
Issue 1
Start page 147
End page 157
Total pages 10
Language eng
Abstract/Summary Propagation and transfer rate coefficients in free-radical polymerizations are calculated from first principles, using quantum calculations (both ab initio and semi-empirical) to determine geometries, frequencies, torsional potentials and energies of reactants and transition state, after which transition state theory yields the Arrhenius parameters. While activation energies can only be calculated for small species and with large computational resources, acceptable frequency factors (A) are obtained with relative ease provided that lower frequencies corresponding to torsions are treated as hindered rotors, not harmonic oscillators; this entails finding the torsional potential and exact evaluation of the corresponding partition function. Simple theory can be used to find A because this involves a ratio of partition functions of reactant and transition state, and because torsions (which are dominated by geometrical considerations) dominate A. A is determined by three modes in the transition state: rotation of the monomer about the forming bond, rotation of a “propylene”-group about the terminal C–C bond in the radical, and simultaneous bending of the two angles associated with the forming bond. Calculations on ethylene and acrolein give agreement with experiment. These studies explain some experimental observations. (i) Changing the penultimate unit gives a small but significant change in the torsion of two of the three modes dominating A, leading to a penultimate-unit effect of ca. a factor of 1–10. (ii) Deuteration affects the moments of inertia of the torsions, leading to changes in A in accord with experiment. (iii) A, but not the activation energy, changes predictably along a homologous series (e.g., methyl, butyl methacrylate). (iv) For a given monomer, A's for transfer to monomer and propagation are similar.
Keyword Free-radical polymerization
Consistent values
Rate parameters
Copolymerization
Systems
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ
Additional Notes Article first published online: 4 March 2011.

Document type: Conference Paper
Collection: Centre for Nutrition and Food Sciences Publications
 
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Created: Mon, 07 Mar 2011, 15:47:47 EST