Accessing the chain length dependence of the termination rate coefficient for disparate length radicals via reversible addition fragmentation chain transfer chemistry: A theoretical study

On the basis of the recently introduced reversible addition fragmentation chain transfer chain length dependent termination (RAFT-CLD-T) method, a novel approach is presented to access the termination rate coefficient for disparate length radicals, Kts.l. In-depth simulation is employed to validate this approach, which utilizes reversible addition fragmentation chain transfer (RAFT) chemistry to generate two nearly monodisperse chain length distributions with disparate average lengths, s and l. These disparate length radicals are generated by prepolymerizing a polyRAFT species to a chain length significantly greater than unity and subsequently progressing the polymerization of the polyRAFT species in the presence of a suitable RAFT agent of initial chain length 1. The present study demonstrates that the chain length dependence of the termination rate coefficient for disparate length radicals can be obtained accurately regardless of the extent of the prepolymerization period of the polyRAFT species, the input kinetic parameters, and whether the geometric or the harmonic mean approximation is assumed for the relationship between k t and the individual radical chain lengths s and l. Thus, for the first time a facile and accurate method for quantification of kt s,l; is validated theoretically allowing for a complete characterization of free radical termination processes for disparate length radicals. © 2006 American Chemical Society

Mapping photolysis product radical reactivities via soft ionization mass spectrometry in acrylate, methacrylate, and itaconate systems

Electrospray ionization-quadrupole ion trap mass spectrometry (ESI-MS) was utilized to access the polymeric product spectrum generated by the pulsed laser polymerization (PLP) of methyl acrylate (MA) at -35 °C in the presence of the photoinitiators 2,2-dimethoxy-2-phenylacetophenone (DMPA), benzoin, benzoin ethyl ether (BEE), and bis(2,4,6-trimethylbenzoyl)phenylphosphinoxide (Irgacure 819) to study the reactivity of primary and potential secondary derived radical fragments from photolytically induced fragmentation. Similarly, the polymeric products generated from the PLP of dimethyl itaconate (DMI) at 0 °C using the aforementioned photoinitiators as well as benzil and 2,2′- azobis(isobutyronitrile) (AIBN) were studied using ESL-MS. The PLP products of methyl methacrylate (MMA) initiated with Irgacure 819 at -25 °C were also examined: Polymerization systems utilizing Irgacure 819 give complex product spectra due to the formation of second generation radical species resulting in several initiator fragments incorporated into a single polymer chain. Termination products, both combination and disproportionation, were identified with high accuracy. The reactivity of the various derived radical fragments toward the monomers employed is summarized for the current and a previous study in tabular form. Energy deposition into the MA/photoinitiator systems is found to have no influence on the product distributions of the MA polymers produced via photoinitiation under the conditions examined. For various photoinitiators employed, products congruent to that of chain transfer to monomer species in the DMI photopolymerizations are observed, conclusively illustrating that chain transfer to monomer is a significant reaction pathway in itaconate free radical polymerizations. © 2007 American Chemical Society