Vapor-based initiator coatings for atom transfer radical polymerization

A novel polymeric initiator coating for surface modification via atom transfer radical polymerization (ATRP) is reported. The synthetic approach involves the chemical vapor deposition of [2.2]paracyclophane-4-methyl 2-bromoisobutyrate and can be applied to a heterogeneous group of substrates including stainless steel, glass, silicon, poly(dimethylsiloxane), poly(methyl methacrylate), poly(tetrafluoroethylene), and polystyrene. Surface analysis using X-ray photoelectron spectroscopy and Fourier-transformed infrared spectroscopy confirmed the chemical structure of the reactive initiator coatings to be consistent with poly[(p -xylylene-4-methyl-2-bromoisobutyrate)-co-(p-xylylene)]. Appropriate reactivity of the bromoisobutyrate side groups was confirmed by surface initiated atom transfer radical polymerization of a oligo(ethylene glycol) methyl ether methacrylate. After solventless deposition of the CVD-based initiator coating, hydrogel films as thick as 300 nm could be conveniently prepared within a 24 h timeframe via ATRR Moreover, the polymerization showed ATRP-specific reaction kinetics and catalyst concentration dependencies. In addition, spatially controlled deposition of the initiator coatings using vapor-assisted microstructuring in replica structures resulted in fabrication of spatially confined hydrogel microstructures. Both protein adsorption and cell adhesion was significantly inhibited on areas that were modified by surface-initiated ATRP, when compared with unmodified PMMA substrates. The herein described initiator coatings provide a convenient access route to controlled radical polymerization on a wide range of different materials. While demonstrated only for a representative group of substrate materials including polymers, metals, and semiconductors, this method can be expected to be generically applicable - thereby eliminating the need for cumbersome modification protocols, which so far had to be established for each substrate material independently.