TEMPO driven thiol–ene reaction for the preparation of polymer functionalized silicon wafers

Abstract

TEMPO driven thiol–ene reaction was utilized to prepare silicon (Si) wafers modified with a variety of polymer brushes, such as poly(N-isopropyl acrylamide), polystyrene, poly(isobornyl acrylate), poly(acrylic acid), and functionalized cysteine. In order to confirm the functionalization of Si wafers using TEMPO driven thiol–ene reaction, initially model reactions were performed between 3-mercaptopropyltriethoxysilane with various enes such as n-butyl acrylate, N,N′-dimethylacrylamide, divinyl sulfone, 1-dodecene, and vinyltriethoxysilane. The model reactions exhibited quantitative conversion under methanol, tetrahydrofuran, and chloroform at 35 °C. For polymer functionalization of Si wafers, thiol and ene functionalized polymers have been prepared by reversible addition fragmentation chain-transfer (RAFT) and high-temperature polymerization. The synthesized thiol and ene functionalized polymers were characterized using ¹H NMR spectroscopy, UV-visible spectroscopy, size exclusion chromatography (SEC), dynamic light scattering, and zeta potential analysis. The ene functionalized monomers, for example, cysteine functionalized with ene (Cys-Ene) and 3-mercapopropyltriethoxysilane functionalized with ene (MPTES-Ene) were prepared by the reaction between cysteine/3-mercaptopropyltriethoxysilane with 1,4-bis(acryloyloxy)butane under mild reaction conditions again through thiol–ene chemistry initiated by TEMPO at 35 °C for 16 h. The synthesized Cys-Ene and MPTES-Ene have been characterized by ¹H and ¹³C NMR spectroscopy. Furthermore, thiol/ene-functionalized Si wafers (Si–SH/Si–Ene) were prepared using thiol (MPTES) and ene (MPTES-Ene) functionalized silanizing agents. Finally, thiol/ene functionalized polymers and ene functionalized cysteine were conjugated on thiol/ene functionalized Si wafers under mild reaction conditions. The polymer/cysteine functionalized Si wafers have been characterized through contact angle measurement, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The antifouling characteristic of Si wafer functionalized with cysteine was studied using fluorescence microscopy after treatment with albumin–fluorescein isothiocyanate conjugate.