Abstract
Creating strong joints between dissimilar materials for high-performance hybrid products places high demands on modern adhesives. Traditionally, adhesion relies on the compatibility between surfaces, often requiring the use of primers and thick bonding layers to achieve stable joints. The coatings of polymer brushes enable the compatibilization of material surfaces through precise control over surface chemistry, facilitating strong adhesion through a nanometer-thin layer. Here, we give a detailed account of our research on adhesion promoted by polymer brushes along with examples from industrial applications. We discuss two fundamentally different adhesive mechanisms of polymer brushes, namely (1) physical bonding via entanglement and (2) chemical bonding. The former mechanism is demonstrated by e.g., the strong bonding between poly(methyl methacrylate) (PMMA) brush coated stainless steel and bulk PMMA, while the latter is shown by e.g., the improved adhesion between silicone and titanium substrates, functionalized by a hydrosilane-modified poly(hydroxyethyl methacrylate) (PHEMA) brush. This review establishes that the clever design of polymer brushes can facilitate strong bonding between metals and various polymer materials or compatibilize fillers or nanoparticles with otherwise incompatible polymeric matrices. To realize the full potential of polymer brush functionalized materials, we discuss the progress in the synthesis of polymer brushes under ambient and scalable industrial conditions, and present recent developments in atom transfer radical polymerization for the large-scale production of brush-modified materials.
Highlights
Most products today are hybrids manufactured by combining a number of materials to optimize functionality, performance, and price
Adhesion is obtained either via physical interactions where the polymer brushes unify with the bulk polymer material through interpenetration and entanglement, or via chemical crosslinks where reactive groups in the polymer brush react and form covalent bonds to the bulk polymer melt
E.g., epoxy, polyurethane, and acrylic adhesives utilize both chemical and physical bonds, the ability of polymer brushes to interpenetrate into bulk polymer matrices enables a unique mode of interaction in terms of chain entanglement
Summary
Most products today are hybrids manufactured by combining a number of materials to optimize functionality, performance, and price. Polymer brushes represent an exciting new opportunity to achieve precise control of surface chemistry, enhance material compatibility, and allow the introduction of reactive functional groups to enable strong chemical bonding. Adhesion is obtained either via physical interactions where the polymer brushes unify with the bulk polymer material through interpenetration and entanglement, or via chemical crosslinks where reactive groups in the polymer brush react and form covalent bonds to the bulk polymer melt. E.g., epoxy, polyurethane, and acrylic adhesives utilize both chemical and physical bonds, the ability of polymer brushes to interpenetrate into bulk polymer matrices enables a unique mode of interaction in terms of chain entanglement. Functional groups introduced in the polymer brush in the post-polymerization modification may react and form covalent bonds to the adherend e.g., at elevated temperatures or with pressure in a molding process
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