Construction of hydroxyl-terminated poly(N-isopropylacrylamide) brushes on silicon wafer via surface-initiated atom transfer radical polymerization

摘要

Surface-initiated atom transfer radical polymerization (SI-ATRP) of N-isopropylacrylamide (NIPAM) on silicon wafer in the presence of 2-mercaptoethanol (ME) chain transfer agent was conducted in attempt to create controllable hydroxyl-terminated brushes. The initiator-immobilized substrate, was prepared by the esterification of hydroxyl groups on silicon wafer with 2-bromopropionyl bromide (2-BPB); followed by the ATRP of NIPAM using a catalyst system, that is, Cu(I)Br/2,2'-bipyridine (2,2'-bpy) and a chain transfer agent, that is, ME. The formation of homogeneous tethered poly(N-isopropylacrylamide) (poly(NIPAM) brushes with hydroxyl endgroup, whose thickness can be tuned by chancing ME concentration, is evidenced by using the combination of grazing angle attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, atomic force microscopy, gel permeation chromatography, and water contact-angle measurements. The calculation of grafting parameters from experimental measurements indicated the synthesis of densely grafted poly(NIPAM) films with hydroxyl end-group on silicon wafer and allowed us to predict a ME concentration for forming a "brush" conformation for the chains.