A process to form a block copolymer comprising two or more regions or segments of differentiated polymer composition or properties, including feeding a first mixture that includes a chain shuttling agent, a solvent, the one or more monomers, and optionally hydrogen into a first reactor or reactor zone, feeding a second mixture that includes at least one olefin polymerization catalyst and at least one cocatalyst into the first reactor or reactor zone, contacting the first mixture and the second mixture under polymerization conditions in the first reactor or reactor zone to form a reaction mixture that is characterized by the formation of polymer chains from the monomers, allowing polymerization to occur in the first reactor or reactor zone and/or a second reactor or reactor zone to form polymer chains that are differentiated from the polymer chains, such that the resultant polymer has two or more chemically or physically distinguishable blocks.