Controlled synthesis of high molecular weight telechelic polybutadienes by ring-opening metathesis polymerization

High molecular weight telechelic [dicyano- and dichloro-] polybutadienes (TPBs) have been synthesized via ring-opening metathesis (ROM) polymerization of 1,5-cyclooctadiene (COD) in the presence of the difunctional chain transfer agents (CTAs), 1,4-dicyano- or 1,4-dichloro-2-butene. To achieve high molecular weights, it was critical that the COD monomer contained very low levels of the contaminating, isomeric 4-vinylcyclohexene (VCH), since the latter serves as a competing CTA. An NMR method for determining the level of VCH was developed as well as "reactive purification" strategy in which the VCH was selectively depleted by its (faster) hydroboration. A "two-stage" protocol for preparation of the TPBs was developed wherein a small portion of the eventual charge of COD and the entire quantity of the CTA were first copolymerized to produce telechelic oligomeric butadiene (TOB) of low viscosity. After all of the CTA had been consumed, the remaining COD was charged. This protocol allowed for better MW control and for higher functionality in the resulting TPBs. Finally, diamino-terminated TPBs were prepared by lithium aluminum hydride reduction of the precursor dicyano-TPBs.