How are
Radicals (Re)Generated in Photochemical ATRP?
- Publication date
- Publisher
Abstract
The polymerization mechanism of photochemically
mediated Cu-based
atom-transfer radical polymerization (ATRP) was investigated using
both experimental and kinetic modeling techniques. There are several
distinct pathways that can lead to photochemical (re)generation of
Cu<sup>I</sup> activator species or formation of radicals. These (re)generation
pathways include direct photochemical reduction of the Cu<sup>II</sup> complexes by excess free amine moieties and unimolecular reduction
of the Cu<sup>II</sup> complex, similar to activators regenerated
by electron-transfer (ARGET) ATRP processes. Another pathway is photochemical
radical generation either directly from the alkyl halide, ligand,
or via interaction of ligand with either monomer or with alkyl halides.
These photochemical radical generation processes are similar to initiators
for continuous activator regeneration (ICAR) ATRP processes. A series
of model experiments, ATRP reactions, and kinetic simulations were
performed to evaluate the contribution of these reactions to the photochemical
ATRP process. The results of these studies indicate that the dominant
radical (re)generation reaction is the photochemical reduction of
Cu<sup>II</sup> complexes by free amines moieties (from amine containing
ligands). The unimolecular reduction of the Cu<sup>II</sup> deactivator
complex is not significant, however, there is some contribution from
ICAR ATRP reactions involving the interaction of alkyl halides and
ligand, ligand with monomer, and the photochemical cleavage of the
alkyl halide. Therefore, the mechanism of photochemically mediated
ATRP is consistent with a photochemical ARGET ATRP reaction dominating
the radical (re)generation