Synthesis of acrylamide-based block-copolymer brushes under flow: monitoring real-time growth and surface restructuring upon drying

A series of block-copolymer brushes has been synthesized under continuous flow by surface-initiated, atom-transfer radical polymerization of the acrylamide derivatives: N-isopropylacrylamide (NIPAM), N,N-dimethylacrylamide (DMAM) and N-hydroxyethyl acrylamide (HEAM). The formation of individual blocks was monitored in real time by means of a quartz-crystal microbalance with dissipation monitoring (QCM-D). The chemical composition, as well as the surface properties of the block-copolymer brushes, were examined in their dry state with X-ray photoelectron spectroscopy (XPS) and by measuring the water contact angle following each stage of the polymerization. In most cases, the block-copolymer brushes exhibited surface compositions and properties that closely resembled those of a homopolymer brush of similar composition to the final block. This was not the case when the final block consisted of p(HEAM), where the surface composition and properties were found to resemble those of the penultimate block. XPS depth-profile analysis and dynamic-contact-angle (DCA) measurements indicated that p(HEAM)-terminated block-copolymer brushes undergo interlayer mixing upon drying, driven by surface-energy effects.