Enhancing polymer-polymer adhesion via reactive coupling

We have studied the promotion of interfacial adhesion for a polystyrene/poly(methyl methacrylate) multilayer through the coupling reaction of amine-terminal polystyrene/anhydride-terminal poly(methyl methacrylate). The multilayer is made using a multilayer coextruder. The interfacial adhesion is measured with the asymmetric dual cantilever beam test. The extent of the coupling reaction is quantified with size exclusion chromatography. Interfacial morphology development is measured with atomic force microscopy and transmission electron microscopy.; Slip occurs at the interfaces between immiscible polymer melts at high shear stress. We demonstrate that this can reduce adhesion. When the shear stress experienced by an interface is low, interfacial slip is negligible and interfacial adhesion is high, comparable to a laminated interface. When the shear stress exceeds a critical value, interfacial slip begins and interfacial adhesion starts to decrease with shear stress. Above another critical stress, full slip develops at the interface and adhesion reaches a plateau value, which is about 1/3 of the equilibrium value. The changes in adhesion versus shear stress follow a master curve for different flow rates. This supports the hypothesis that polymer chains at the interface are disentangled by the shear stress during coextrusion. Annealing can restore adhesion on the reptation time scale indicating that entanglements can be reestablished at the interface. The adhesion decrease during coextrusion can also be prevented by adding functional polymers to each layer and creating block copolymers at the interface. The relationship between adhesion and the extent of the coupling reaction is studied quantitatively with a theoretical model.; The interfacial morphology development induced by coupling reaction is also studied. Interface keeps flat or slightly roughened when the interfacial coverage is low. When it is above the saturation coverage, the interface roughens significantly and interfacial emulsification starts. At this stage, micelles or swollen micelles are formed at the interface. Applying shear flows can significantly accelerate the coupling reaction at an interface. We speculate shear flows can increase the possibility of complimentary functional groups to meet with each other at the interface.