A process for producing an elastomer comprising selected copolymerized C.sub.5 -hydrocarbons from a hydrocarbon mixture containing C.sub.5 -monoolefinic hydrocarbons, C.sub.5 -diolefinic hydrocarbons (cyclic and acyclic) C.sub.5 -paraffins, C.sub.6 -aliphatics and benzene which comprises separating the C.sub.5 -hydrocarbons from the mixture and copolymerizing a selected portion of the resulting C.sub.5 -hydrocarbon mixture in the presence of a catalyst system to form an elastomer. The elastomers produced are suitable for use in adhesive compositions in general but particularly useful as a component in pressure sensitive adhesive compositions.