Much
work has been directed to the design of complex single-site
catalysts for ring-opening polymerization (ROP) to enhance both activity
and selectivity. More simply, however, cooperative effects between
Lewis acids and organocatalytic nucleophiles/Lewis bases provide a
powerful alternative. In this study we demonstrate that the combination
of <i>N</i>-heterocyclic carbenes, 1,8-diazabicycloundec-7-ene
(DBU) and 4-dimethylaminopyridine (DMAP) with simple Lewis acids enables
the ROP of the macrolactone pentadecalactone in a rapid and efficient
manner. Remarkably, regardless of the nature of the nucleophile, the
order of activity was observed to be MgX<sub>2</sub> ≫ YCl<sub>3</sub> ≫ AlCl<sub>3</sub> and MgI<sub>2</sub> > MgBr<sub>2</sub> > MgCl<sub>2</sub> in every case. The minimal influence
of
the organobase on polymerization activity allows for the use of simple
and inexpensive precursors. Furthermore, extension of the study to
other cyclic (di)ester monomers reveals the choice of Lewis acid to
lead to monomer selective ROP activity and hence control over copolymer
composition by choice of Lewis acid. This approach could lead to the
realization of complex polymer structures with tunable physical properties
from simple catalyst combinations