Improving the adhesion of polyolefins to glassy polymers is complicated by the semicrystalline nature of the polyolefins. Traditional methods used in glassy polymers to increase the interlayer adhesion, including the addition of a diblock copolymer or the formation of a copolymer through in situ reaction, are still successful with semicrystalline polymers. However, melt miscibility of the adhesion promoting molecules is no longer sufficient; they must also co-crystallize. Even when co-crystallization is achieved, the reactive method is shown to provide greater fracture toughness than the addition of a pre-made diblock copolymer. In the latter case, the formation of micelles limits the efficiency of the diblock copolymer. Finally, significant adhesion enhancement is attainable in reactive systems with contact times as short as 45 seconds as demonstrated through a multilayer coextrusion of amorphous nylon against a polypropylene-maleated polypropylene blend.