UV-Assisted Li+-Catalyzed Radical Grafting Polymerization of Vinyl Ethers: A New Strategy for Creating Hydrolysis-Resistant and Long-Lived Polymer Brushes as a "Smart" Surface Coating.

Abstract

A facile synthetic route was developed to prepare a surface-grafted brush layer of poly(vinyl ethers) (PVEs) directly by a radical mechanism, with the "naked" Li+ acting as a catalyst. Density functional theory calculations suggested that complexation of naked Li+ to VEs significantly reduced the highest unoccupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap from 5.08 to 0.68 eV, providing a better prospect for electron transfer. The structure, morphology, and surface properties of grafted polymer layers were characterized using attenuated total reflection Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and dynamic water contact angle (DCA). Moreover, ellipsometry data indicated that the thickness of the polymer brushes was in the range of 20-60 nm, which corresponds to the grafting densities of 0.65-1.15 chain/nm2, and DCA decreased from 84.4 to 45.3°. Most importantly, no hydrolysis was observed for the modified surface after 30 days of exposure to phosphate-buffered saline solution, 0.1 mol/L NaOH(eq) and 0.1 mol/L HCl(eq), demonstrating excellent hydrolysis resistance with long service life. In addition, as a proof of concept, the side hydroxyl groups of grafted PVEs provide active sites for efficient fixation of bioactive molecules, e.g., glycosaminoglycan and serum protein.