Polydopamine-melanin initiators for Surface-initiated ATRP

Thin films of polydopamine, a melanin-like material formed by the oxidative polymerization of dopamine in aqueous solution, have attracted much recent interest as functional coatings. Here we demonstrate the use of modified polydopamine as an initiator layer for surface-initiated polymerization, synthesized by reacting dopamine with 2-bromoisobutyryl bromide (BIBB) before deposition. Modified polydopamine films grew at a comparable rate to unmodified polydopamine, with a 45 nm being grown in 24 h. The presence of initiator groups was confirmed by XPS and FTIR and by the growth of PMMA and PHEMA polymer brushes. ARGET, the recently-developed oxygen-tolerant variant of ATRP, was used for surface polymerization with sodium ascorbate as the reducing agent. Polymerization was rapid, with PMMA brushes of nearly 240 nm thickness being grown in 24 h. A range of substrates could be coated in this way, including metals and hydrophobic polystyrene, demonstrating the broad applicability of this initiator.