Overcoming the Low Driving Force in Forming Depolymerizable Polymers through Monomer Isomerization.

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. The use of excess triphenylphosphine was found to be essential to suppress secondary metathesis and depolymerization. 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.