Living ring-opening metathesis polymerization of exo-norbornenes bearing both cyano and ester functionalities by a well-defined ruthenium catalyst

Exo-ethyl 3-cyanobicyclo[2.2.1]hept-5-ene-2-carboxylate (A) and exo- ⁿbutyl 3-cyanobicyclo[2.2.1]hept-5-ene-2-carboxylate (B) bearing both cyano and ester groups were subjected to homopolymerization by ring-opening metathesis polymerization with a well-defined Ru catalyst, (H ₂IMes)(3-bromopyridine)₂Cl₂Ru=CHPh (3) (H ₂IMes = M,N′-bis(mesityl)-4,5-dihydroimidazol-2-ylidine) at low temperature. The characterization of the synthesized homopolymers by GPC analyses showed a value of a number-average molecular weight (M_n) as high as 296,000 and a narrow polydispersity index (< 1.06). The results imply that the initiator 3 had a compatibility of the polar functional groups and promoted fairly well-defined living polymerization. The glass transition temperatures of the homopolymers obtained from monomer A were significantly higher than those observed for polymers from monomer B obtained under the same reaction conditions. The rates of homopolymerizations of monomer A, B, and the parent norbornene (C) were determined by the monitoring the consumption of the monomers by the ¹H NMR spectra. It was revealed that the polymerization rate for the homopolymerization of monomer A was almost same as that of monomer B, but much slower than that of C. On the basis of the successful homopolymerization, the synthesis of block and random copolymers derived from monomers A, B, and C via living polymerization using catalyst 3 was also accomplished.