3 research outputs found

    Photoactivated Molecular Layer Deposition through Iodoāˆ’Ene Coupling Chemistry

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    This work introduces photoactivated molecular layer deposition (pMLD) as a route to deposit organic nanoscale polymer films with molecular-level control. Surface-tethered acrylate polymers are obtained through a radical step-growth polymerization where a diene and a diiodo monomer, ethylene glycol dimethacrylate (EGM) and 1,3-diiodopropane (DIP), respectively, are sequentially dosed in the vapor-phase under pulsed UV irradiation. pMLD occurs with a constant growth rate of 3.7 ƅ/cycle, and both monomers display self-limiting saturation. Films deposited by pMLD exhibit excellent stability in organic solvents. Furthermore, annealing studies with in situ X-ray photoelectron spectroscopy (XPS) reveals thermal stability up to 350 Ā°C in vacuum. The mechanism behind pMLD of EGM and DIP is proposed based on detailed characterization of the polymer films by XPS and Fourier transform infrared spectroscopy, growth modeling, and comparison with control studies of pMLD involving monofunctional precursors. The coupling chemistry of pMLD presented herein provides future possibilities to create apolar linkages in the formation of nanoscale organic films

    Electron Transport through a Diazonium-Based Initiator Layer to Covalently Attached Polymer Brushes of Ferrocenylmethyl Methacrylate

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    A versatile method based on electrografting of aryldiazonium salts was used to introduce covalently attached initiators for atom transfer radical polymerization (ATRP) on glassy carbon surfaces. Polymer brushes of ferrocenylmethyl methacrylate were prepared from the surface-attached initiators, and these films were thoroughly analyzed using various techniques, including X-ray photoelectron spectroscopy (XPS), infrared reflectionā€“absorption spectroscopy (IRRAS), ellipsometry, and electrochemistry. Of particular interest was the electrochemical characterization of the electron transfer through the diazonium-based initiator layer to the redox centers in the polymer brush films. It was found that the apparent rate constant of electron transfer decreases exponentially with the dry-state thickness of this layer. To investigate the electron transfer in the brushes themselves, scanning electrochemical microscopy (SECM) was applied, thereby allowing the effect from the initiator layer to be excluded. The unusual transition feature of the approach curves recorded suggests that an initial fast charge transfer to the outermost-situated ferrocenyl groups is followed by a slower electron transport involving the neighboring redox units

    Surface-Attached Poly(glycidyl methacrylate) as a Versatile Platform for Creating Dual-Functional Polymer Brushes

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    Novel types of dual-functional surface-attached polymer brushes were developed by post-polymerization modification of polyĀ­(glycidyl methacrylate) brushes on glassy carbon substrates. Azide and alcohol groups were initially introduced by epoxide ring-openings of the side chains. These polymer brushes represent an attractive chemical platform to deliberately introduce other molecular units at specific sites. In this work, ferrocene and nitrobenzene redox units were immobilized through the two groups to create redox polymers. In-depth analysis by infrared reflectionā€“absorption spectroscopy and X-ray photoelectron spectroscopy revealed an almost quantitative conversion of the modification reactions. The electrochemical activity of the ferrocenyl part of this diode-like system was fully expressed with an electron transfer rate constant = 1.2 s<sup>ā€“1</sup> and surface density = 0.19 nmol cm<sup>ā€“2</sup> per nm section of the film, independent of its thickness. In contrast, for the nitrobenzene moieties diffusion of counterions (i.e., tetraalkylammonium) easily becomes the rate-controlling step, thereby leaving a substantial fraction of them electrochemically inactive