Termination kinetics of dibutyl itaconate free-radical polymerization studied via the SP-PLP-ESR technique

Michael Buback, Mark Egorov, Thomas Junkers, Elena Panchenko

Research output: Contribution to journalArticleResearchpeer-review

50 Citations (Scopus)

Abstract

The termination kinetics of dibutyl itaconate (DBI) bulk polymerization was studied via SP-PLP-ESR single pulse-pulsed laser polymerization With time-resolved detection of free-radical concentration by electron-spin resonance, at temperatures between 0 and 60°C. As is characteristic of PLP experiments, termination rate coefficients, kt(i,i), are measured for radicals of (almost) identical chain length (CL) i. CL-averaged (k t), far chain lengths up to 200 monomer units, and also k t 0 referring to termination of very small-size radicals are directly deduced from measured DBI radical concentration vs time traces. At 45°C, 〈kt〉 is (3.4±0.6) · 105 L · mol-1 · s-1 and kt 0 is (7,2±1.0) · 105 L · mol -1 · s-1. Both rate coefficients are independent of monomer conversion up to the highest experimental conversion of 18%. The associated activation energies are EA(〈kt〉) = 23.0±3.2 kJ · mol-1 and EA(k t 0) = 27.6±2-8 kJ · mol-1, respectively. "Model-dependent" and "model-free" analyses of radical concentration vs time profiles indicate a pronounced CL dependence of kt(i,i) for DBI radicals of moderate size, 5 < i < 50. The lowering of kt(i,i) with CL corresponds to an exponent α close to 0.5 in a power-law expression kt,(i,i) = kt 0 · i-a. At higher chain lengths the variation of k t(i,i) with CL becomes weaker and may be represented by an α value of 0.16 or even below. These results are consistent with models according to which a varies to a larger extent at low CL and to a smaller extent at high CL with the crossover region between the two ranges being located somewhere around i = 100.

Original languageEnglish
Pages (from-to)333-341
Number of pages9
JournalMacromolecular Chemistry and Physics
Volume206
Issue number3
DOIs
Publication statusPublished - 3 Feb 2005
Externally publishedYes

Keywords

  • ESR/EPR
  • Kinetics (polym.)
  • Pulsed laser polymerization
  • Radical polymerization
  • Termination kinetics

Cite this