A polymer composition useful in making products produced by extrusion, molding, film and thermoforming processes, comprises optionally a matrix polymer, a nanofiller, and a polyolefin with functional groups that has been prepared directly by polymerizing olefin monomers with comonomers comprising functional groups using a single site catalyst. An independent claim is included for a use of a polyolefin with functional groups that has been prepared directly by polymerizing olefin monomers with comonomers comprising functional groups using a single site catalyst as a compatibilizer in a polymer composition comprising optionally a matrix polymer and a nanofiller.