Chemical Modification of Polymer Brushes via Nitroxide Photoclick Trapping

Abstract

The preparation of polymer brushes (PBs) bearing α-hydroxyalkylphenylketone (2-hydroxy-2-methyl-1-phenylpropan-1-one) moieties as photoreactive polymer backbone substituents is presented. Photoreactive polymer brushes with defined thicknesses (up to 60 nm) and high grafting densities are readily prepared by surface initiated nitroxide mediated radical polymerization (SINMP). The photoactive moieties can be transformed via Norrish-type I photoreaction to surface-bound acyl radicals. Photolysis in the presence of a persistent nitroxide leads to chemically modified PBs bearing acylalkoxyamine moieties as side chains resulting from trapping of the photogenerated acyl radicals with nitroxides. Application of functionalized nitroxides to the photochemical PB postmodification provides functionalized PBs bearing cyano, polyethylene glycol (PEG), perfluoroalkyl, and biotin moieties. As shown for one case, photochemical postfunctionalization of the PB through a mask using a biotin-conjugated nitroxide as the trapping reagent leads to the corresponding site-selective chemically modified PB, which is successfully used for site-specific streptavidin immobilization. Surface analysis of PBs was performed by contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), attenuated total reflection (ATR), fourier transform infrared (FTIR) spectroscopy, and fluorescence microscopy.

Dynamic Nitroxide Functional Materials

“…Importantly, they have been extensively employed for the preparation of well‐defined and complex macromolecular architectures . NRC “click”‐type reactions between persistent nitroxide free radicals and transient carbon‐centered alkyl radicals (e.g., generated in situ from alkyl halides or photoinitiators)– typically yield spin‐captured alkoxyamine functional units with the dynamic covalent character of the generated NO−C bond. This remarkable feature of reversible alkoxyamine switches enables covalent bonding and debonding on demand and has promoted the manufacturing of programmable polymer scaffolds, ranging from refoldable single‐chain polymer nanoparticles to dynamic polymer materials with self‐healing properties .…”

Post‐polymerization modification by nitroxide radical coupling

“…Indeed, this photochemical post-polymerization modification method is very tolerant to different functional groups and was successfully applied also to the site-selective immobilization of streptavidin using a biotin-conjugated nitroxide on a silicon wafer modified with a PS block. 127 A similar approach was applied recently by Su et al 128 for the preparation of , -heterotelechelic polymers. In this case, two photoactive polymers (PS and poly(tert-butyl acrylate)) with alkoxyphenyl ketone moieties as photochemical active sites at the backbone were synthesized by ATRP.…”

“…The PS block was also anchored to a silicon wafer. Indeed, this photochemical post‐polymerization modification method is very tolerant to different functional groups and was successfully applied also to the site‐selective immobilization of streptavidin using a biotin‐conjugated nitroxide on a silicon wafer modified with a PS block …”

Efficient Photochemical Approaches for Spatially Resolved Surface Functionalization

“…Studer and co-workers adapted this strategy to the functionalization of polymer brushes obtained by surfaceinitiated nitroxide-mediated polymerization [40] of 2-hydroxy-2-methyl-1-(4-vinylphenyl)propan-1-one,astyrene derivative able to play the dual role of monomer and photoinitiator. [41] Irradiation (LED, l = 365 nm) was performed over 4-5 hi n the presence of biotinylated, perfluorinated, or triethylene glycol bearing TEMPO derivatives to yield the modified brushes,a sevident by water contact angle measurements, XPS,and astreptavidin assay.Asimilar strategy was applied to the functionalization of zeolites. [42] Owing to the large range of commercially available or reported TEMPO derivatives,a sw ell as the tolerance of many reactive groups towards radicals,t he photoinduced radical-trapping method is extremely versatile with regard to patterned molecules.F or example,p roteins are routinely labeled with TEMPO.…”