Ruthenium-Catalyzed Cascade Metathetical Cyclopolymerization of Bisnorbornenes with Flexible Linkers

Treatments of bisnorbornenes tethered by a flexible linker (triethylene glycol, tetramethylene moiety, or crown ether) with the first generation of Grubbs catalyst give the corresponding single-stranded polybisnorbornenes via cascade metathetical cyclopolymerization (CMCP). The structures of these polymers were proved by spectroscopic means, MALDI-TOF mass spectrometry, gel permeation chromatography, and dynamic light scatterings as well as by chemical degradation via hydrolysis followed by esterification. The presence of N-aryl pendants to connect the norbornene moiety and the flexible linker is crucial for the success of such CMCP process. Presumably, intramolecular π–π interactions between the pending aryl groups may take place to direct the ring closure process. Substrates without such N-aryl pendants give a mixture of single- and double-stranded polynorbornenes in addition to cross-linking polymers.