Stretching decelerates ring-opening metathesis at cis-olefins in stressed molecular bows.

Ring-opening metathesis polymerization (ROMP) of strained cycloalkenes, driven by angle strain relief, has emerged as a powerful and versatile approach for synthesizing macromolecular materials. Nevertheless, the ROMP of C=C bonds upon stretching remains unexplored. Here, we employ a molecular-strain engineering approach by incorporating stretched C=C bonds into bowstrings of molecular bows (MBs) with different tension levels. This approach enables us to investigate the ROMP of the C=C bonds under varying tensile forces. Remarkably, increased tensile force applied to the cis-C=C bond leads to significant deceleration of the ROMP reaction, whereas the trans-isomer exhibits a pronounced acceleration under the same conditions. This contrasting response was theoretically established to originate from the differential strain-induced modulation of the activation energy. Critically, applied tensile force thus governs directly both the kinetics and mechanistic pathway of ROMP, selectively promoting cyclic oligomer formation and establishing a molecular-strain-engineering paradigm that transcends conventional ring-strain-driven polymerization.