Architectural Editing of Polyesters and Polyurethanes via Palladium(II)-Catalyzed [3,3]-Sigmatropic Oxo-Rearrangements

Architecture
underlies the thermomechanical properties of polymers.
Yet, few strategies are available to tune a polymer’s architecture
after it is prepared without altering its chemical composition. The
ability to edit the architecture of a polymer would dramatically expand
the accessible architecture-property space of polymeric materials.
Herein, we disclose a backbone rearrangement approach to tune the
short-chain branching of polymers. Specifically, we demonstrate that
palladium(II)-catalyzed [3,3]-sigmatropic oxo-rearrangements can transform
branched polyesters and polyurethanes to their linear counterparts.
While the effects on materials properties are generally subtle in
the case of polyesters, more dramatic changes are observed in the
case of polyurethanes: two polyurethanes undergo a soluble-to-insoluble
transition, and one exhibits a dramatic increase in both strain at
break and toughness after rearrangement. Additionally, the incorporation
of alkenes in the polymer backbone through the rearrangement enables
facile deconstruction via ethenolysis. In all, we disclose a powerful
and broad-scope strategy to edit the architecture of polymer backbones
and thereby tune their physical and chemical properties.