RING-OPENING METATHESIS POLYMERIZATION OF BICYCLO [2.2.1]HEPT-2-ENE (2-NORBORNENE) AND EXO,EXO-5,6-BIS(METHOXYCARBONYL)-7-OXABICYCLO [2.2.1]HEPT-2-ENE USING RU(II) AND RU(III) COMPLEXES - POLYMERIZATION KINETICS AND RUTHENIUM CONTENT IN POLYMERS

Bicyclo [2.2.1] hept-2-ene (2-norbornene, 1) and exo,exo-5,6-bis(methoxycarbonyl)-7-oxabicyclo [2.2.1]hept-2-ene (2) were polymerized with the Ru complexes [Ru(H2O)6]tos2, [Ru(II)(eta6-benzene)(H2O)3]tos2 (tos=p-toluenesulfonate) and RuCl3.3H2O. It is shown that the aqueous ROMP with these catalysts is not a living polymerization, since molecular weights are almost independent of the polymerization time and of the monomer to catalyst ratio. Molecular weight distributions are broad, typically more than 1.5-2. Yields depend strongly on both the monomer and the catalyst concentration, are difficult to reproduce and seldom reach values above 80-90%. These observations are explained by the proposed reaction mechanism, with a slow and sensitive initiation step followed by a fast propagation and termination by occlusion or blocking of the catalyst within the polymer. It was not possible to reduce the Ru content in these polymers below a certain level (250-300 ppm), which corresponds to ca. one Ru atom per polymer chain. Therefore complete recycling of the catalyst solutions is not possible due to catalyst depletion.