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The Role of Cu0 in Surface-Initiated Atom Transfer Radical Polymerization: Tuning Catalyst Dissolution for Tailoring Polymer Interfaces

Fantin, Marco, Ramakrishna, Shivaprakash N., Yan, Jiajun, Yan, Wenqing, Divandari, Mohammad, Spencer, Nicholas D., Matyjaszewski, Krzysztof, Benetti, Edmondo M.
Macromolecules 2018 v.51 no.17 pp. 6825-6835
acrylamides, catalysts, copper, ligands, organic halogen compounds, polymerization, polymers, quartz crystal microbalance, reducing agents
The availability of catalytic/reducing sites at metallic Cu⁰ sources during supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) is regulated by the components of the polymerization mixture, including ligand (L), alkyl halide initiator (R–X), and Cuᴵᴵ-based deactivator. Their contributions were analyzed by quantifying the dissolution of Cu species within a quartz crystal microbalance with dissipation (QCM-D), subjecting a Cu⁰-coated sensor to different polymerization mixtures. The control of catalyst diffusion from Cu⁰ was subsequently exploited to fabricate structured polymer brushes with diverse compositions, when ATRP was performed from surface-immobilized initiators in the presence of a Cu⁰ plate, placed at a determined distance (d) from the substrate. Surface-initiated ATRP in the presence of Cu⁰ (Cu⁰-SI-ATRP) is compatible with a broad variety of monomers, including oligo(ethylene glycol) acrylate (OEGA), methyl acrylate (MA), and acrylamide (AAm). The kinetics of brush growth is finely tuned by the independent variation of d, polymerization time, and concentration of added deactivator. Modulation of these parameters allowed us to generate homopolymer and multiblock copolymer brush gradients featuring a variety of morphologies and controlled interfacial properties, with unprecedented spatial resolution over the brush structure.