Wohl‐Ziegler Bromination of Electrografted Films for Optimizing Atom Transfer Radical Polymerization

Abstract

Electrografting of aryldiazonium compounds to conducting surfaces is extensively used to alter the surface properties. The highly reactive aryl radical is the actual grafting reagent, which on one hand is pertinent for the efficiency of the procedure but, on the other hand, in some cases is problematic by introducing unwanted side reactions. The electrografting of e.g. 4‐(bromomethyl)benzenediazonium is often carried out with the aim of creating a film that may serve as initiator for a controlled atom transfer radical polymerization. Unfortunately, this is difficult to accomplish because of bromine abstraction reactions occurring during the grafting process, which diminish the bromine content of the grafted layer significantly. Yet, this problem may be resolved by enriching the initiator film with bromine through a Wohl‐Ziegler bromination prior to the polymerization. An alternative pathway consisting of grafting 4‐methylbenzenediazonium followed by a bromination reaction to introduce bromine atoms at the benzylic position is shown to work equally well. Additionally, bromination of grafted benzyl alcohol groups have been explored. Finally, the repaired bromine films are used as a platform for atom transfer radical polymerization.

A post-functionalization toolbox for diazonium (electro)-grafted surfaces: review of the coupling methods

“…The first one is focused on the grafting of cyclam-functionalized polyglycidyl methacrylate on carbon fibers for copper adsorption 216 while the second one, published by a Danish team, highlights the limits of direct immobilization of the brominated initiator due to bromine abstraction reactions occurring during the grafting process. 217 This parasitic reaction, which lower the bromine concentration of the grafted layer, can be circumvent by enriching the film with bromine through a Wohl-Ziegler bromination before the ATRP. Other authors have chosen to prepare initiator-modified surfaces by a two-step procedure including first the electrochemical reduction of aryl diazonium salts to produce active layers and second the post-functionalization of the modified substrate with the initiator.…”