Light-Controlled Switchable Ring Opening Polymerization

Light is a fascinating
source of external stimulus for the regulation
of polymerization processes. In this contribution, some salicylaldimine
Zn­(II) complexes bearing azobenzene moieties were prepared and characterized.
Isomerization between the trans and cis forms of these complexes is
achieved by exposure to light; both isomers are active in the ring-opening
polymerizations of ε-caprolactone (CL), rac-lactide, trimethylene carbonate, β-oxetanone, δ-valerolactone,
cyclopentadecanolide, and 5-methyl-5-propyl-1,3-dioxan-2-one but exhibit
different kinetic profiles. A 6-fold reactivity difference was realized
for the ring-opening polymerization of CL upon irradiation with light.
The light-induced isomerization also led to reactivity discrimination
between different monomers in copolymerization reactions. Reversible
photoswitching between two catalytically active states provides a
fascinating strategy for the control of polymerization processes,
as well as the compositions of the polymers produced.