Electrochemically-controlled grafting of hydrophilic brushes from conducting polymer substrates

Electrochemically-mediated ATRP (eATRP) has emerged in recent years as an alternative controlled radical polymerisation technique that utilises low concentrations of copper-based ATRP catalysts, and that can be conducted in the presence of atmospheric oxygen. In this work, we adapt eATRP to perform surface-initiated electrografting directly from a conducting polymer (CP) macroinitiator that also acts as the working electrode to control catalyst oxidation state, and thereby catalyst activity. Aqueous electrografting of hydrophilic poly(2-hydroxyethyl methacrylate) polymer brushes from the CP macroinitiator, in the presence of an ATRP catalyst (CuBr2/TPMA), was confirmed by ATR-FTIR, water contact angle measurements, and XPS. Optimised grafting conditions were determined whereby polymerisation kinetics approached first order characteristics, as expected for grafting via an eATRP mechanism. However, even under these optimised conditions, we determined that competing electrografting mechanisms were likely occurring, with experiments supporting the occurrence of polymerisation in solution, followed by ‘grafting to’ reactions, as previously described for electrografting via surface electroinitiated emulsion polymerisation (SEEP). Additionally, spectroelectrochemical studies suggest that the mechanism of initiation differs from previously reported eATRP systems in that the conducting polymer itself acts as a co-reductant for the catalyst. As expected, the prevalence of uncontrolled grafting, due to competing grafting mechanisms, as well as effects such as chain termination and degrafting, was highly dependent on polymerisation conditions, most notably on the applied potential.

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