Chapter 3: Bifunctional and Supramolecular Organocatalysts for Polymerization

Bimolecular, H-bond mediated catalysts for ring-opening polymerization (ROP)—thiourea or urea plus base, squaramides and protic acid/base pairs, among others—are unified in a conceptual approach of applying a mild Lewis acid plus mild Lewis base to effect ROP. The bimolecular, and other supramolecular catalysts for ROP, produce among the best-defined materials available via synthetic polymer chemistry through a delicately balanced series of competing chemical reactions by interacting with substrate at an energy of <4 kcal mol⁻¹. These catalysts are among the most controlled available for ROP. Part of this arises from the modular, highly tunable nature of dual catalysts, which conduct extremely controlled ROP of a host of cyclic monomers. The broader field of organocatalytic polymerization is a bridge between the disparate worlds of the materials chemist (ease of use) and the synthetic polymer chemist (mechanistic interest). The cooperative and collegial nature of the organocatalysis for the ROP community has facilitated the synergistic evolution of new mechanism to new abilities—in monomer scope, polymer architecture and level of reaction control.