Supramolecular Polymer Brushes

Thin polymer coatings present a method to modify the surface properties of underlying substrates. Polymer-coated surfaces have been used as anticorrosive materials, surfaces with special wetting properties, antifriction materials, and as materials for biomedical applications. Polymer brushes are a type of coating in which polymer chains are tethered to a surface. While almost all known polymer brushes are attached via covalent bonds, supramolecular, or non-covalently tethered polymer brushes, are less explored. However, tethering of polymer brushes via supramolecular interactions could pave the way to stimuli-responsive, "smart", and self-healing surfaces. The work presented here aims to investigate the formation of supramolecular polymer brushes with different preparation methods and supramolecular motifs to understand the effects that determine supramolecular brush formation. This will be achieved by i) comparing two supramolecular motifs with different binding constants and ii) comparing the "grafting from" method with the "grafting to" method for both binding motifs.Chapter 1 presents a literature overview of supramolecular polymer brushes prepared via the "grafting to" and the "grafting from" approach. Most supramolecular polymer brushes are prepared via the "grafting to" method, typically by block copolymer physisorption or through non-covalent interactions. There is less research in the preparation of supramolecular polymer brushes by a "grafting from" approach. Chapter 2 aims to investigate the preparation of supramolecular polymer brushes with the "grafting from" approach. For this purpose, cucurbit[7]uril (CB[7]), a macrocyclic host molecule, is mono-functionalized with a propargyl group and tethered onto silicon substrates via copper-catalysed azide-alkyne cycloaddition. A supramolecular initiator is formed upon complex formation with an ammonium adamantane-functionalized bromo isobutyrate derivate. The formation of supramolecular polymer brushes is investigated by using subsequent surface-initiated atom transfer radical polymerization (SI-ATRP). Furthermore, spatially controlled deposition of the guest/initiator molecules is used for the formation of patterned surfaces. Chapter 3 investigates the influence of the intrinsic complex stability on the formation of supramolecular polymer brushes by exchanging the binding motif to a weaker complex. For this purpose, CB[7] is exchanged by ß-cyclodextrin (ß-CD), which forms a complex with the same ammonium adamantane guest, however, with a binding constant that is 9 orders of magnitude lower than the ammonium adamantane@CB[7] complex. Also in this case, a monopropargyl derivate of ß-CD is synthesized and immobilized onto silicon substrates via copper-catalysed azide-alkyne cycloaddition. The resulting surfaces are exposed to the ammonium adamantane-functionalized bromo isobutyrate derivate to form the supramolecular initiator. Additionally, the polymerization protocol and monomers detailed in chapter 2 allowed for a direct comparison of the two supramolecular motifs. Chapter 4 demonstrates the preparation of supramolecular polymer brushes via the "grafting to" method, using the same host-guest complexes as in chapter 2 and chapter 3. Ammonium-adamantane-terminated poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) polymers with various molecular weights are prepared via solution ATRP and subsequently exposed to CB[7]- or ß-CD- modified silicon substrates.