Synthesis and Mechanochemical Activation of Ladderene-Norbornene Block Copolymers

We have recently reported a polymechanophore system, polyladderene (PLDE), which dramatically transforms into polyacetylene (PA) upon mechanical stimulation. Herein, we optimized conditions to synthesize unprecedented block copolymers (BCPs) containing a force-responsive block by sequential ring-opening metathesis polymerization of different norbornenes and bromoladderene. Successful extension from PLDE to other blocks required careful timing and low temperatures to preserve the reactivity of the PLDE-appended catalyst. The PLDE-containing BCPs were sonochemically activated into visually soluble PA with a maximum absorption λ ≥ 600 nm and unique absorption patterns corresponding to noncontinuous activation of ladderene units. Access to polymechanophore BCPs paves the way for new stress-responsive materials with solution and solid state self-assembly behaviors and incorporation of polymechanophores into other materials.