This invention relates to a process for forming a long-chain branched polymer and a long-chain branched polymer resulting from the process. The process comprises reacting (a) a polyolefin base polymer with (b) a coupling agent comprising a polymeric coupling agent, optionally blended with a molecular coupling agent, the polymeric coupling agent being a modified polyolefin having a reactive coupling group at one or more terminal ends of the modified polyolefin chain, to couple the polyolefin base polymer (a) with the coupling agent (b) to form a long-chain branched polymer having a long-chain branching and/or higher surface energy relative to the polyolefin base polymer.