Abstract: Polymeric hydrocarbons having reactive borane groups at chain ends or in the polymer chain are described. These types of polymers can be used as intermediate materials for preparing a broad range of polymers which have functional groups located at both ends of the polymer chain (telechelic polymers). The process of preparing the borane-containing polymers involves metathesis degradation of the polymer at the double bond locations in the backbone and simultaneous functionalization of the broken chain ends by borane monomers. Depending on the nature of the borane monomer, the location of boron atoms can be controlled to be at either the chain ends (telechelic) or in the polymer backbone. The concentration of boron in the resulting polymer is related to the reaction time and the mole ratio between borane monomer and the double bonds in the starting hydrocarbon polymer. In turn, the borane groups are interconvertible to various functional groups, such as OH, NH.sub.2, and halides, under mild reaction conditions.