Chemically Circular Poly(orthoester) Elastomers via Immortal Cationic Ring-Opening Polymerization

Synthetic polymers present a unique challenge: while essential to modern life and produced on a global scale exceeding 400 Mt scale annually, their detrimental ecological impact warrants an urgent response to develop more sustainable solutions. Poly(orthoesters) are a promising yet underutilized class of degradable polymers with demonstrated utility in drug release applications; however, challenges in their synthesis have hindered further study of their potential as deconstructable plastics. Herein, we report the first example of a molecular weight-controlled synthesis of a poly(orthoester) (up to Mn = 149 kDa) by cationic ring-opening polymerization of a spirocyclic orthoester monomer. The simultaneous high reactivity and coordinating nature of the orthoester monomer posed significant challenges, necessitating the development of a tridentate halogen bond donor catalyst to selectively promote reversible-deactivation polymerization while suppressing undesired monomer activation. Mechanistic studies revealed that the immortal nature of the polymerization enables molecular weight control, with chain livingness maintained despite irreversible termination reactions, owing to degenerative chain transfer through the poly(orthoester) backbone. The demonstrated scalability, controlled degradation, quantitative chemical recycling to monomer, and tunable material properties highlight poly(orthoesters) as a promising platform for the development of sustainable, circular, and high-performance plastics.