Ring-opening metathesis polymerization of 7-methylbicyclo[2.2.1]hepta-2,5-diene initiated by well-defined molybdenum and ruthenium carbene complexes

Polymers of 7-methylnorbornadiene (7-MNBD) have been prepared by ring-openi ng metathesis polymerization (ROMP) using Mo(=CHCMe2Ph)(=NC6H,-2,6-i-Pr-2)( OR), [1, OR=OCMe(CF3)(2); 2, OR=OCMe3], Mo(=CHCMe,)(=NC6H3-2,6-i-Pr-2)(OR)( 2) (2') and Ru(=CHPh)Cl-2(PCy3)(2) (3) as initiators in CD2Cl2. The structu res of the polymers were investigated by H-1- and C-13-NMR spectroscopy. In all cases the ROMP was very fast and the initial product was essentially a polymer of anti units, linked by 88% cis double bonds for initiation by 1, 68% for 2 or 2', and 17% for 3. The tacticities of the polymers varied fro m atactic using 1 as initiator to fully tactic (t/m and dr) using 2 or 2' a s initiator. Values of k(p),k(i) were derived from the proportion of initia tor consumed and the initial ratio of monomer to initiator: k(p)/k(i) = 550 for 1, 1100 for 2, 64 for 2', and 61 for 3. Two kinds of secondary reactio n were observed: the first gave rise to a second set of C-13-NMR peaks (10- 20% of the intensity of the main peaks), and the second, observed only with 1, was characterised by sudden gelation of the reaction mixture some time after the monomer had been consumed, and was followed by a marked fall in t he intensity of the main C-13-NMR peaks. These effects are attributed to se condary intra- and inter-molecular metathesis reactions, respectively. The high-trans polymer could be fully hydrogenated, but the high-cis polymer co uld only be partially hydrogenated. (C) 2000 Elsevier Science S.A. All righ ts reserved.