A new precursor for conducting polymer-based brush interfaces with electroactivity in aqueous solution Lisa T. Strover a, d , Jenny Malmström a , Olivia Laita b , Jóhannes Reynisson b , Nihan Aydemir a , Michel K. Nieuwoudt b , David E. Williams a, d , P. Rod Dunbar c , Margaret A. Brimble b , Jadranka Travas-Sejdic a, d, * a Polymer Electronics Research Centre, School of Chemical Sciences, University of Auckland, New Zealand b School of Chemical Sciences, University of Auckland, New Zealand c School of Biological Sciences, University of Auckland, New Zealand d MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand article info Article history: Received 19 June 2012 Received in revised form 4 November 2012 Accepted 29 November 2012 Available online 26 December 2012 Keywords: Conducting polymer Molecular brush Stimuli-responsive surface abstract We present the synthesis of a novel conducting polymer (CP) incorporating both pyrrole and thiophene units in its monomer, which is also substituted with an initiator for grafting of sidechains by atom-transfer radical polymerisation (ATRP). The precursor monomer for the CP macroinitiator, 2-(2,5-di(pyrrol-2-yl) thiophen-3-yl)ethyl 2-bromopropanoate) (PyThon) is very readily electropolymerised at low monomer concentrations and low applied potentials. Density functional theory (DFT) predictions of ionisation po- tentials and spin-charge distribution for PyThon are in good agreement with these experimental results. We present also the grafting of sidechains from electropolymerised PolyPyThon (PPyThon) to yield surface- confined polymer brushes. Functionalisation with polystyrene (PS), poly(2,3,4,5,6-pentafluorostyrene) (PFS) and poly(ethylene glycol) methyl ether acrylate (PEGMEA) is demonstrated and confirmed by FT-IR and water contact angle measurements. These PPyThon-based molecular brushes are electroactive in both water and acetonitrile, and show evidence of changes in surface conformation related to the redox state of the CP. The growth of human fibroblasts on PPyThon films is also demonstrated, indicating good biocompatibility of the polymer. We conceive PPyThon-based molecular brushes as a substrate for elec- trical stimuli-responsive surfaces with application particularly in the biomedical field. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, significant progress has been made in the design of functional and stimuli-responsive surfaces for applications including microfluidics, self-cleaning surfaces, and biomedical ap- plications [1]. In this regard, conducting polymers (CPs) are a promising class of materials. CPs possess a conjugated structure and are readily switched between an oxidised (conductive) and neutral (insulating) state by electrical stimulus in an appropriate electrolyte solution. Oxidation and reduction is accompanied by the influx and efflux of dopant ions (along with solvent) to balance charge [2]. The stimuli-responsive characteristic of conducting polymers is derived from a combination of transitions of chemical, electrical and mechanical properties that accompany their oxidation and reduction [1a]. The reversible doping of CPs has been exploited for the design of stimuli-responsive surfaces with switchable wettability [1d,3]. Among the most commonly studied CPs are polypyrrole (PPy), polyaniline (PANi), and polythiophene and its derivatives [2a]. Mo- lecular brushes based on these CPs have been described in the lit- erature, primarily as a means to improve or alter properties of the backbone CP to enhance their utility. Research has focussed on improving solubility [4], processability/mechanical properties [4c,5], regioregularity [4a], and optical and electronic properties [4b,f,g,6] as well as optimising the morphology of CP-containing copolymers for photovoltaic applications [7]. CP-based molecular brushes have also been used to take advantage of properties of grafted chains for applications such as electrodes and sensing which make use of the electrochemical activity of the CP substrate [8]. With respect to biomedical applications, Kang et al. have described a range of CP-based molecular brushes with functional groups suitable for protein and enzyme immobilisation [4d,e]. CP-based molecular brushes that combine the electroactivity of PANi backbones and the * Corresponding author. Polymer Electronics Research Centre, School of Chemical Sciences, University of Auckland, Auckland 1003, New Zealand. Tel.: þ64 9373 7599x88272; fax: þ64 9373 7422. E-mail address: j.travas-sejdic@auckland.ac.nz (J. Travas-Sejdic). Contents lists available at SciVerse ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymer.2012.11.083 Polymer 54 (2013) 1305e1317