Polymerizability of cycloalkenes in “living” ring-opening metathesis polymerization initiated by Schrock complexes: 3. effect of monomer structure.

The kinetics of the “living” and “controlled” ring-opening metathesis homo- and copolymerization of several cycloalkenes initiated by Mo-based Schrock complexes were investigated in the context of a general study devoted to the relation between the monomer structure on its reactivity. First, the polymerizability of these monomers was measured as a function of both their ring strain and their bulkiness. In a second part, the intrinsic reactivity of both the monomers and the corresponding active centers was evaluated from the determination of the rate constants of homopropagation and the various reactivity ratios. The steric hindrance created by the monomer substituents has only a small effect on the intrinsic reactivity of the cycloalkene. The latter mainly depends on the ring strain exactly as does the polymerizability. Steric crowding around the acyclic double bonds of the polymer chain is another factor affecting the reactivity of the active propagating centers; the latter is indeed found to depend on the capability of these acyclic double bonds to compete with the double bond of the cyclic monomer for the complexation to the transition metal.