Chain Transfer during the Aqueous Ring-Opening Metathesis Polymerization of 7-Oxanorbornene Derivatives

Ring-opening metathesis polymerization (ROMP) of exo,exo-5,6-bis(methoxymethyl)-7-oxabicyclo[2.2.1]hept-2-ene (3) catalyzed by Ru^II(H₂O)₆(tosh (tos = p-toluenesulfonate) (1) in the presence of terminal acyclic olefins such as 3-buten-l-ol and methyl acrylate affords low molecular weight polymeric materials. Analysis of these oligomer samples by one- and two-dimensional ^lH NMR spectroscopy identifies them as resulting from a true metathesis chain transfer mechanism. These data and the identification of the ring-opened monomer units with alkylidene end groups corresponding to the acyclic chain transfer agent by high resolution mass spectrometry confirm this study as the first example of metathesis of an acyclic olefin by 1. A comparison of the chain transfer activities of a series of acyclic esters yields a reactivity order of terminal olefins > deactivated terminal olefins > internal olefins > deactivated internal olefins, consistent with the behavior of well-characterized homogeneous alkylidene complexes.