Characterization of self-assembled Bis[2-(2-bromoisobutyryloxy) undecyl] disulphide (DTBU) on gold surfaces suitable for use in surface-initiated atom transfer radical polymerization (SI-ATRP)

Abstract

• Initiator DTBU on gold electrode (SAM) enhances electrochemical mediation ATRP. • CV, EIS, CA, XPS and IRRAS methods are used for DTBU monolayer characterization. • Well organized DTBU SAM with polar head and non-polar inside. • EIS, CA and IRRAS prove preferential presence of 6MP in mixed SAM with DTBU. • Mixed monolayers with 6MP provide optimal conditions for adaptation and use in e-ATRP. Bis[2-(2-bromoisobutyryloxy) undecyl] disulphide (DTBU) is an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP) able to functionalize metal surfaces through formation of self-assembled monolayers (SAM). The goal of this work is the making monolayers with the DTBU initiator on gold polycrystalline electrodes and their study by electrochemical methods as cyclic voltammetry (CV), capacity-potential curves (C-E), electrochemical impedance spectroscopy (EIS), and angle contact measurements for their characterization. Information of the integrity and permeability of the monolayers has been obtained by capacitance-potential measurements and impedance spectra. Also, the blocking effect of the physical barrier that SAM can produce to different redox probes is explored by using voltammetry and impedance. DTBU forms a compact monolayer whose main features are related with heterogeneous chain structures, having a non-polar hydrocarbon internal part and a polar head group. This is confirmed by X-ray photoelectron spectroscopy (XPS) which shows the presence of the elements of the DTBU adsorbate of SAM. Moreover, mixed monolayers of DTBU and 6-mercaptopurine (6MP) have been prepared and characterized, to check if the thiol facilitates electron exchange through monolayers. On this approach, different DTBU:6MP ratios have been employed and characterized studying IRRAS spectra, electrochemical properties, and contact angle on the modified surface. These mixed monolayers provide optimal conditions for adaptation and use in e-ATRP.