Synthesis of end-functionalized poly(norbornene)s via ring-opening metathesis polymerization

The synthesis of a variety of poly(norbornene)s (PNB)s bearing acetoxy, hyd roxy, and vinyl end groups was accomplished. PNBs with an acetoxy group at one terminus and a vinyl group at the other were prepared using norbornene, ruthenium-based olefin metathesis catalyst (PCy3)(2)Cl2Ru double bond CHPh , and allyl acetate as a chain transfer agent (CTA). Employing a more activ e catalyst, (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene)(PCy3)Cl2Ru double bond CHPh, and 1,4-diacetoxy-2-butene as the CTA afforded telechelic PNBs bearing acetoxy groups at both ends of the polymer chains. Molecular weight s were controlled by varying the initial monomer/CTA ratio and were in agre ement with their theoretical values. Using a similar procedure, acetoxy end -terminated PNBs were also obtained by degradation of high molecular weight PNB. Removal of the acetoxy groups afforded the corresponding hydroxy-term inated polymers with number-averaged functionalities close to two. Mechanis ms are proposed for the formation of the end-functionalized polymers. Corre ction factors for characterizing PNBs by gel permeation chromatography (GPC ) are also suggested.