Synthesis of dihydroxy poly(ethylene-co-butadiene) via metathetical depolymerization: Kinetic and mechanistic aspects

We investigate the synthesis of dihydroxytelechelic poly(ethylene-co-1,3-butadiene) via metathetical depolymerization of the corresponding high molar mass copolymers in the presence of first generation Grubbs catalyst and butene diacetate as functionalizing chain transfer agent, followed by hydrolysis of the acetoxy chain ends. Formation of telechelic oligomers is complicated by a fast back-biting reaction leading to cyclohexene and macrocycles production. The thermodynamically favored formation of unsaturated six membered ring results from the presence of 1,7-dienic unsaturations in the starting copolymer. Macrocycles also rapidly and almost quantitatively form in the first reaction stage. Opportunely they can re-open in the presence of functionalizing transfer agent, owing that the later is introduced in molar excess with respect to the macrocycle, finally yielding linear dihydroxytelechelic oligomers.