In Situ Observation of Chemical Reactions at Buried Solid/Solid Interfaces in Coextruded Multilayer Polymer Films

The characterization of chemical reactions at the buried interface is critical to understand interfacial molecular interactions and improve interfacial properties like adhesion. Interface-sensitive sum frequency generation (SFG) vibrational spectroscopy can probe the buried interface in situ nondestructively. While SFG has been used to study many model polymer interfaces, it has never been applied to study multilayer polymer films produced on commercial coextrusion lines. Here, we apply SFG to elucidate the molecular details of chemical reactions at the buried interface in multilayer cast films consisting of maleic anhydride (MAH)-modified Tie layers promoting the adhesion between polyamide and polyethylene. We demonstrated the utility of SFG to identify the reaction products from the interfacial reaction between MAH and polyamide with varying MAH concentrations and to monitor changes of the interfacial molecular orientation. The developed approach is generally applicable to probe chemical reactions and molecular interactions at buried interfaces in multilayer polymer films.