While depolymerizable polymers have been intensely pursued as a potential solution to address the challenges in polymer sustainability, most depolymerization systems are characterized by a low driving force in polymerization, which poses difficulties for accessing diverse functionalities and architectures of polymers. Here, we address this challenge by using a cyclooctene-based depolymerization system, in which the cis-to-trans alkene isomerization significantly increases the ring strain energy to enable living ring-opening metathesis polymerization at monomer concentrations ≥ 0.025 M. An additional trans-cyclobutane fused at the 5,6-position of the cyclooctene reduces the ring strain energy of cyclooctene, enabling the corresponding polymers to depolymerize into the cis-cyclooctene monomers. Importantly, the use of excess triphenylphosphine (PPh3) was found to be essential to suppress secondary metathesis and depolymerization. Using the living polymerization, we demonstrate the preparation of depolymerizable block copolymers and bottlebrush polymers. The high-driving-force living polymerization of the trans-cyclobutane fused trans-cyclooctene system holds promise for developing chemically recyclable polymers of a wide variety of polymer architectures.

Synthesis of depolymerizable polymers with well-defined architectures enabled by Cis-to-trans isomerization of cyclooctene

ACS Spring 2022

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