Termination Kinetics of Dibutyl Itaconate Free-Radical Polymerization Studied via the SP–PLP–ESR Technique

✍ Scribed by Michael Buback; Mark Egorov; Thomas Junkers; Elena Panchenko

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 158 KB
• Volume: 206
• Category: Article
• ISSN: 1022-1352
• DOI: 10.1002/macp.200400358

✦ Synopsis

Abstract

Summary: 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, k~t~(i,i), are measured for radicals of (almost) identical chain length (CL) i. CL‐averaged 〈k~t~〉, for chain lengths up to 200 monomer units, and also k referring to termination of very small‐size radicals are directly deduced from measured DBI radical concentration vs time traces. At 45 °C, 〈k~t~〉 is (3.4 ± 0.6) · 10^5^ L · mol^−1^ · s^−1^ and k is (7.2 ± 1.0) · 10^5^ 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 E~A~(〈k~t~〉) = 23.0 ± 3.2 kJ · mol^−1^ and E~A~(k) = 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 k~t~(i,i) for DBI radicals of moderate size, 5 < i < 50. The lowering of k~t~(i,i) with CL corresponds to an exponent α close to 0.5 in a power‐law expression k~t~(i,i) = k · 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 α 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.

Conversion‐dependence of 〈k~t~〉 and k from laser‐induced photopolymerization of DBI.

imageConversion‐dependence of 〈k~t~〉 and k from laser‐induced photopolymerization of DBI.