Synthesis of poly(N-isopropylacrylamide) on initiator-modified self-assembled monolayers

This report describes a convenient method for in situ polymerization of the environmentally responsive polymer, poly(N-isopropylacrylamide) (PNIPAAM), on the surfaces of azo-initiator-derivatized self-assembled monolayers (SAMs) of omega -terminated alkanethiolates on gold. In contrast to previous methods for initiation of free radical polymerization from SAM surfaces, this method utilizes simple chemistry and commercially available precursors. Carboxylic acid-containing SAMs were derivatized with the azo-initiator, 2,2'-azobis(2-amidinopropane) hydrochloride, by first activating the carboxylic acid moieties with Woodward's reagent K. The initiator-containing samples were used to initiate polymerization at the surface. The process was enhanced by the dilution of the carboxylic acid species within the monolayer. The resulting tethered PNIPAAM surfaces were characterized using ellipsometry, X-ray photoelectron spectroscopy, and contact angle goniometry and tested for their ability to attach and release bacteria. The synthetic method is especially useful for preparing ultrathin polymer films that are compatible with common reflection (e.g., surface plasmon resonance) and transmission based optical characterization techniques.