Non‐Delaminating Polymer Hydrogel Coatings via C,H‐Insertion Crosslinking (CHic)—A Case Study of Poly(oxanorbornenes)

Abstract

Robust, non‐delaminating polymer coatings and hydrogels are needed for technical and biomedical applications. This study focuses on surface‐attached poly(oxanorbornene) hydrogels obtained by simultaneous UV‐activated crosslinking and surface‐immobilization. The synthesis and copolymerization of two oxanorbornene monomers carrying the UV‐crosslinkers malonic acid diazoester or benzophenone, which can both undergo UV‐triggered C,H‐insertion crosslinking (CHic), is presented. The crosslinking efficiency and network stability of hydrogels made from these self‐crosslinkable polymers are studied and compared to the properties of poly(oxanorbornene) networks obtained by UV‐triggered thiol‐ene‐reactions involving a low molecular weight crosslinker. Smooth, defect‐free, non‐delaminating hydrogel coatings are obtained by CHic, not only on laboratory model surfaces but also on a technical product.

Self‐Regenerating Antimicrobial Polymer Surfaces via Multilayer‐Design—Sequential and Triggered Layer Shedding under Physiological Conditions

“…Instead of using an additional small molecule crosslinker, the poly(guanidinium oxanorbornene) 1 with a small fraction of crosslinkable diazoester‐functionalized repeat units was synthesized ( Figure a). UV irradiation of these units trigger C,H‐insertion reactions with neighboring polymer segments, so that homogeneously crosslinked poly(guanidinium oxanorbornene) layers were obtained . Since it is analytically difficult to prove layer shedding from a polymer multilayer stack, the basic crosslinkable poly(guanidinium oxanorbornene) polymer 1 (Figure a) was further modified with different fluorescent groups: with the green‐fluorescent nitrobenzoxadiazol ( 1a , Figure a), the red‐fluorescent rhodamine B ( 1b , Figure a), and the blue‐fluorescent coumarin group ( 1c , Figure a) .…”

“…The synthesis of the fluorescent and nonfluorescent antimicrobial poly(guanidinium oxanorbornenes) shown in Figure was performed in analogy to previously reported similar polymers and is described in Section of the Supporting Information. In short, the respective monomers (Figure S1, Supporting Information) where mixed in the appropriate ratios and polymerized in dichloromethane using Grubbs' 3rd generation catalyst.…”

“…[23b] After spin coating, the layer was UV irradiated to form a network. The 3‐EBP groups formed covalent bonds to the substrate, and the diazoester groups formed covalent bonds to other polymer chain segments by C,H insertion chemistry . Thus, the surface‐attached polymer network A was obtained.…”

“…This was close to the thickness of the original A layer and indicated that the non‐crosslinked A′ layer was removed in the aqueous medium, as expected. The slight decrease in layer thickness of A after regeneration can be explained by extraction of unbound polymer from layer A . To demonstrate quantitative removal of the A′ layer (which is crucial to prove true surface regeneration), fluorescence microscopy images were recorded during assembly and disassembly of the A–A′ system ( Figure ).…”

“…Monomers, polymers, and surface functionalization agents were synthesized as described in the literature. [18-20,23a,31] Polymer solutions were filtered through CHROMAFIL hydrophilized polytetrafluoroethylene (h‐PTFE) syringe filters (13 mm, 0.2 µm) from Macherey‐Nagel, Düren, Germany prior to application. As substrates silicon wafers from SiMat Silicon Materials, Kaufering, Germany were used and silanized with 3‐EBP as described previously .…”