Abstract: This invention is a solution process for the preparation of ethylene-.alpha.-olefin/diolefin copolymers comprising contacting ethylene, one or more .alpha.-olefin monomer, and optionally one or more diene monomer, with a catalyst system containing a catalyst activator and a Group 4 metallocene compound, comprising a) conducting the polymerization reaction at a temperature of about 60.degree. to 150.degree. C.; b) selecting as the Group 4 metallocene compound one or more members of the group consisting of cyclic monocyclopentadienyl Group 4 metal and covalently bridged (bis)indenyl hafnium metallocene compounds; and c) maintaining the .alpha.-olefin concentration at a molar ratio to that of ethylene of between about 0.3 to 7.0 and a diolefin to ethylene molar ratio of between about 0.01 and 0.4. In a preferred embodiment the process comprises: 1) mixing with a reaction solvent the one or more .alpha.