Fabrication of Thiol–Ene “Clickable” Copolymer-Brush Nanostructures on Polymeric Substrates via Extreme Ultraviolet Interference Lithography

Abstract

We demonstrate a new approach to grafting thiol-reactive nanopatterned copolymer-brush structures on polymeric substrates by means of extreme ultraviolet (EUV) interference lithography. The copolymer brushes were designed to contain maleimide functional groups as thiol-reactive centers. Fluoropolymer films were exposed to EUV radiation at the X-ray interference lithography beamline (XIL-II) at the Swiss Light Source, in order to create radical patterns on their surfaces. The radicals served as initiators for the copolymerization of thiol-ene "clickable" brushes, composed of a furan-protected maleimide monomer (FuMaMA) and different methacrylates, namely, methyl methacrylate (MMA), ethylene glycol methyl ether methacrylate (EGMA), or poly(ethylene glycol) methyl ether methacrylate (PEGMA). Copolymerization with ethylene-glycol-containing monomers provides antibiofouling properties to these surfaces. The number of reactive centers on the grafted brush structures can be tailored by varying the monomer ratios in the feed. Grafted copolymers were characterized by using attenuated total reflection infrared (ATR-IR) spectroscopy. The reactive maleimide methacrylate (MaMA) units were utilized to conjugate thiol-containing moieties using the nucleophilic Michael-addition reaction, which proceeds at room temperature without the need for any metal-based catalyst. Using this approach, a variety of functionalities was introduced to yield polyelectrolytes, as well as fluorescent and light-responsive polymer-brush structures. Functionalization of the brush structures was demonstrated via ATR-IR and UV-vis spectroscopy and fluorescence microscopy, and was also indicated by a color switch. Furthermore, grafted surfaces were generated via plasma activation, showing a strongly increased wettability for polyelectrolytes and a reversible switch in static water contact angle (CA) of up to 18° for P(EGMA-co-MaMA-SP) brushes, upon exposure to alternating visible and UV-light irradiation.

Multifunctional and Transformable ‘Clickable’ Hydrogel Coatings on Titanium Surfaces: From Protein Immobilization to Cellular Attachment

“…Thermal treatment unmasks the maleimide groups to their thiol- and diene- reactive form and yields hydrogels ready for functionalization with nucleophilic thiol-ene and Diels–Alder reactions ( Figure 2 a). Successful the retro Diels–Alder reaction to unmask maleimide groups was confirmed using ATR-FTIR, from the shift of C=O stretching vibration band to a higher wavenumber ( Figure 2 b), similar to previous reports in the literature [ 47 , 49 , 59 ].…”

“…Among all ‘clickable’ units, the maleimide functional group attracts attention due to their facile reaction with thiol- and furan-containing molecules under mild conditions [ 41 , 42 , 43 , 44 ]. We have earlier reported maleimide-containing polymers [ 45 , 46 ], surfaces [ 47 , 48 , 49 , 50 ] and bulk hydrogels [ 51 ] for biomolecular immobilization [ 52 , 53 ]. In a recent study, copolymers containing dopamine- and maleimide-containing monomers were used to obtain antibacterial coatings on titanium surfaces through attachment of anti-bacterial peptides [ 54 ].…”

SuFEx on the Surface: A Flexible Platform for Postpolymerization Modification of Polymer Brushes

“…Also,t he functionalization of reactive polymer brushes through highly efficient forms of postpolymerization modification (PPM) reactions has emerged as an expanding field. [11][12][13][14][15][16][17] By combining the unique properties of polymer brushes and click chemistry PPM, surfaces with desirable and unique properties can be quickly generated without laborious monomer or polymer synthesis.The ability to use avariety of coupling strategies,especially highly robust and efficient click chemistries,i sp articularly important for decorating surfaces with multiple functionalities. [18][19][20][21] However,s ome click reactions have inherent drawbacks such as oxygen sensitivity or difficult synthetic access.O ur lab has already demonstrated several uses of PPM click chemistry on polymer brushes to design complex interfaces.…”

The Taming of the Maleimide: Fabrication of Maleimide‐Containing ‘Clickable’ Polymeric Materials

“…Hence, it is of importance to develop fabrication methods that would enable growth of these polymer chains on substrates other than glass/silicon oxides. In a recent study by Padeste and coworkers, maleimide containing polymeric brushes were grown from a polymeric substrate, namely, poly(ethylene‐alt‐tetrafluoroethylene) (ETFE) (Figure ) . Patterned thiol‐ene clickable functional copolymer brushes were fabricated on polymeric substrates by applying extreme ultraviolet (EUV) interference lithography.…”

“… (a) Synthesis of copolymer brushes via grafting from plastic substrate and the subsequent retro Diels−Alder (rDA) reaction, (b) post‐polymerization modification with thiol‐containing spiropyran, (c) reversible color switching of P(EGMA‐co‐MaMA‐SP) brushes upon exposure to visible and UV‐light . Copyright © 2015, American Chemical Society.…”