Highly efficient syntheses of acetoxy- and hydroxy-terminated telechelic poly(butadiene)s using ruthenium catalysts containing N-heterocyclic ligands

Bis(acetoxy)-terminated telechelic poly(butadiene) (PBD) with molecular weights controllable up to 3.0×104 have been prepared via the ring-opening metathesis polymerization (ROMP) of cyclooctadiene when 1,4-bis(acetoxy)-2-butene was included as a chain transfer agent (CTA). The polymerizations were catalyzed by a highly active ruthenium catalyst 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) (PCp3)(Cl2Ru=CHCHC(CH3)2 (Cp=cyclopentyl) (6) with monomer/catalyst ratios as high as 9.8×104. Removal of the acetoxy groups with sodium hydroxide afforded hydroxy end-terminated telechelic PBD (HTPBD). Examination of the telechelic PBDs revealed an exclusive 1,4-PBD microstructure with a predominately trans geometry (up to 90%). The high activity and stability of 6 permitted a one-step synthesis of HTPBD using the unprotected free alcohol, 2-butene-1,4-diol, as the CTA.