Increasing Adhesion via Strong Dipoles: Oxazolidinone-containing Polyolefins as Nonreactive Tie Layers in Polymer Laminates

Multilayer films are widely used to combine the properties of multiple polymers but often require tie layers to achieve interfacial adhesion between the substrates. To adhere polar and nonpolar polymers, common tie layers are polyolefins containing reactive functionalities, which limit their application space and potential methods for multilayer recycling. By contrast, nonreactive tie layers require chemical modification to achieve suitable performance due to their relatively weak dipoles. To address this limitation, we synthesized a series of hydrogenated copolymers between 1,5-cyclooctadiene and an oxazolidinone-fused cyclooctene monomer (Oxa, 10–100 mol %) to form “polyethylene” functionalized with strong dipoles (~5 Debye). We tested these copolymers as nonreactive tie layers between high-density polyethylene (HDPE) and polyamide 6 (PA6), achieving adhesive strengths up to 881 N/m with moderate dipole incorporation. We observed a change in the interface of adhesive failure from PA6 to HDPE with increasing Oxa content, demonstrating a change in substrate affinity with increasing polarity. Overall, this work provides the first evidence of strong dipoles increasing interfacial adhesion for nonreactive tie layers, introducing a new adhesive design strategy for multilayer polymeric materials.