Zinc oxide (ZnO) was previously reported as an excellent
cocatalyst
for mechanically controlled atom transfer radical polymerization (mechanoATRP),
but its photocatalytic properties in photoinduced ATRP (photoATRP)
have been much less explored. Herein, well-defined ZnO nanocrystals
were prepared via microwave-assisted synthesis and applied as a heterogeneous
cocatalyst in mechano- and photoATRP. Both techniques yielded polymers
with outstanding control over the molecular weight, but ZnO-cocatalyzed
photoATRP was much faster than analogous mechanoATRP (conversion of
91% in 1 h vs 54% in 5 h). The kinetics of photoATRP was tuned by
loadings of ZnO nanocrystals. PhotoATRP with ZnO did not require any
excess of ligand versus Cu, in contrast to mechanoATRP, requiring
an excess of ligand, acting as a reducing agent. ZnO-cocatalyzed photoATRP
proceeded controllably without prior deoxygenation, since ZnO was
involved in a cascade of reactions, leading to the rapid elimination
of oxygen. The versatility and robustness of the technique were demonstrated
for various (meth)acrylate monomers with good temporal control and
preservation of end-group functionality, illustrated by the formation
of tailored block copolymers.