Preparation of block copolymers by ring‐opening polymerization of cycloalkenes initiated by a tungstencyclopentylidene complex

Abstract

AbstractThe possibility of making block copolymers at room temperature from the monomer pairs 2a,b/1, 4/1, 5/1 and 5/3 (1 = norbornene = bicyclo[2.2.1]hept‐2‐ene; 2a,b = anti‐ and syn‐7‐methylbicyclo[2.2.1]hept‐2‐ene; 4 = methyl endo‐bicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate; 5 = endo‐bicyclo[2.2.1]hept‐5‐ene‐2‐carbonitrile; 3 = 1,5‐cyclooctadiene) was explored using as initiator of metathesis polymerization in CD2Cl2. The reactions of successive small amounts of the monomers with the catalyst were first followed by 1H NMR to determine the rate of the reaction and the stability of the metal‐carbene propagating species. AB and ABA type block copolymers were prepared on this basis and analysed by GPC. An increase in molecular weight after each addition was observed in most cases. Secondary metathesis reactions of double bonds in the polymer chains appear to be significant only for blocks formed from 3.