Zwitterionic copolymerization: Synthesis of cyclic gradient copolymers

How to get rich fast: The zwitterionic copolymerization of δ-valerolactone (VL) and ε-caprolactone (CL) provides an expedient route to cyclic gradient copolymers. The faster ring-opening of VL relative to CL with N-heterocyclic carbenes, coupled with sufficiently long lifetimes of the growing zwitterions leads to a polymer structure comprised of VL-rich sequences that transition to CL-rich sequences in a cyclic macromolecule (see scheme). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.