Entropy Drives the Predictive Discovery of an Optimal Cleavable Comonomer for ROMP

Ring-opening metathesis polymerization (ROMP) of norbornene derivatives enables access to polymeric materials for applications ranging from targeted drug delivery to high-performance thermosets; however, the carbon-carbon backbones of ROMP-derived poly-(norbornenes) resist deconstruction under mild, selective conditions. Cleavable comonomers (CCs) have been introduced to address this limitation, yet their implementation has been hindered by prohibitive costs and/or suboptimal reactivity. Moreover, the discovery of existing CCs has been largely empirical, lacking clear design principles. Here, we identify the entropy of ring-opening as one of the key determinants of ROMP copolymerization behavior of the best-performing CCs reported to date. Guided by this insight, we establish predictive design criteria and introduce Me ₄ Si ₂ O9, a CC that exhibits near-ideal room temperature copolymerization with a broad range of norbornene-based (macro)-monomers. Me ₄ Si ₂ O9 is significantly less expensive than leading silyl ether-based CCs and enables uniform incorporation of cleavable linkages into polymer backbones at low loadings. Beyond delivering a cost-effective and high-performance CC, this work provides fundamental insights into ROMP copolymerization that will enable predictive CC development and expand the functional scope of deconstructable polymeric materials.