ABSTRACT
Ought to their bioinert properties and facile synthesis, poly[(oligoethylene glycol)methacrylate]s (POEGMAs) have been raised as attractive alternatives to poly(ethylene glycols) (PEGs) in an array of (bio)material applications, especially when they are applied as polymer brush coatings. However, commercially available OEG-methacrylate (macro)monomers feature a broad distribution of OEG lengths, thus generating structurally polydisperse POEGMAs when polymerized through reversible deactivation radical polymerization. Here, we demonstrate that the interfacial physicochemical properties of POEGMA brushes are significantly affected by their structural dispersity, i.e., the degree of heterogeneity in the length of side OEG segments. POEGMA brushes synthesized from discrete (macro)monomers obtained through chromatographic purification of commercial mixtures show increased hydration and reduced adhesion when compared to their structurally polydisperse analogues. The observed alteration of interfacial properties is directly linked to the presence of monodisperse OEG side chains, which hamper intramolecular and intermolecular hydrophobic interactions while simultaneously promoting the association of water molecules. These phenomena provide structurally homogeneous POEGMA brushes with a more lubricious and protein repellent character with respect to their heterogeneous counterparts. More generally, in contrast to what has been assumed until now, the properties of POEGMA brushes cannot be anticipated while ruling out the effect of dispersity by (macro)monomer feeds. Simultaneously, side chain dispersity of POEGMAs emerges as a critical parameter for determining the interfacial characteristics of brushes.
ABSTRACT
Achieving tolerance toward oxygen during surface-initiated reversible deactivation radical polymerization (SI-RDRP) holds the potential to translate the fabrication of polymer brush-coatings into upscalable and technologically relevant processes for functionalizing materials. While focusing on surface-initiated photoinduced atom transfer radical polymerization (SI-photoATRP), we demonstrate that a judicious tuning of the composition of reaction mixtures and the adjustment of the polymerization setup enable to maximize the compatibility of this grafting technique toward environmental conditions. Typically, the presence of O2 in the polymerization medium limits the attainable thickness of polymer brushes and causes the occurrence of "edge effects", i.e., areas at the substrates' edges where continuous oxygen diffusion from the surrounding environment inhibits brush growth. However, the concentrations of the Cu-based catalyst and "free" alkyl halide initiator in solution emerge as key parameters to achieve a more efficient consumption of oxygen and yield uniform and thick brushes, even for polymerization mixtures that are more exposed to air. Precise variation of reaction conditions thus allows us to identify those variables that become determinants for making the synthesis of brushes more tolerant toward oxygen, and consequently more practical and upscalable.
ABSTRACT
Polymer brushes are densely grafted, chain end-tethered assemblies of polymers that can be produced via surface-initiated polymerization. Typically, this is accomplished using initiators or chain transfer agents that are covalently attached to the substrate. This manuscript reports an alternative route towards polymer brushes, which involves the use of non-covalent cucurbit[7]uril-adamantane host-guest interactions to surface-immobilize initiators for atom transfer radical polymerization. These non-covalent initiators can be used for the surface-initiated atom transfer radical polymerization of a variety of water-soluble methacrylate monomers to generate supramolecular polymer brushes with film thicknesses of more than 100â nm. The non-covalent nature of the initiator also allows facile access to patterned polymer brushes, which can be produced in straightforward fashion by drop-casting a solution of the initiator-modified guest molecules onto a substrate that presents the cucurbit[7]uril host.