This disclosure relates to olefin polymerization catalysts and compositions, their manufacture, and the production of polyolefins using specific catalyst compositions, including the use of chain-shuttling agents in the olefin polymerization process. Specifically, this disclosure provides for dual-headed and multi-headed chain shuttling agents (CSAs or MSAs) and for their use in preparing blocky copolymers. By controlling the ratio of dual-headed and multi-headed CSA sites to mono-headed CSA sites, a blocky copolymer can be provided having properties such as a narrow molecular weight distribution and/or improved melt properties.