Elucidation of the mechanism of surface‐initiated atom transfer radical polymerization from a diazonium‐based initiator layer

Abstract

This study elucidates the influence of the atom transfer radical polymerization initiator structure, monolayer versus disordered multilayer, on the growth kinetics and the structural transition of poly(methyl methacrylate) (PMMA) brush layers. The multilayer initiator film, prepared by acylation of the electrografted 2‐phenylethanol layer using 2‐bromoisobutyryl bromide, consists of ∼4.6 times more tert‐butyl bromide groups compared to monolayer initiator prepared by self assembly technique. The results demonstrate the formation of precursor complex between CuI catalyst and the bromine initiator as a prerequisite step before the onset of polymerization. Furthermore, the PMMA brushes formed by the polymerization from the multilayered initiator layer at 50 °C are 20‐fold thicker compared to the polymerization at 25 °C due to the swelling of the multilayered initiator film. In contrast, the thickness of the PMMA layer on the monolayer initiator is less affected by the polymerization temperature. By varying the initiator density on the surface, the solvent content in the PMMA layer is shown to vary from 15% to 94%, resulting in the transition from concentrated over semidiluted to diluted brushes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

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

“…In contrast, using the enriched GCBnBr* film, the results were much more encouraging in that polymer brushes of ∼15 nm thickness became available. These results are in line with a previous study , showing the importance of having a high initiator density to enable the formation of stretched brush structures. For the GCBnBr* an increase in the oxygen was seen during the Wohl‐Ziegler bromination, which may arise from reaction of the benzylic radical with trace amounts of oxygen forming hydroxyl groups.…”

“…In the case of X=CH 2 Br the organic films are of particular interest, having served as radical initiators in ATRP processes to generate surface‐attached polymer brushes . Both the density and thickness of the polymer brush films are to a high extent determined by the bromine density . Here, it is shown that the bromine abstraction reaction lowers the quality of the initiator film significantly but, also, that the film can be repaired by enriching its content of bromine using a Wohl‐Ziegler bromination prior to the ATRP.…”

High‐ versus Low‐Quality Graphene: A Mechanistic Investigation of Electrografted Diazonium‐Based Films for Growth of Polymer Brushes

“…The dry state thicknesses of the PMMA layer on Ni‐Gra‐PMMA Y is on average 10.1 ± 1.0 nm (corrected for the thickness of the initiator films and including both batches) with a tendency of a slight increase going from Y = 1 to 5. Surprisingly, the increase in atomic concentration of Br for batch #1 from 1.8% for Ni‐Gra‐Br 1 to 3.0% for Ni‐Gra‐Br 5 recorded in XPS is not reflected in the formation of a substantially thicker polymer film, which, otherwise, is seen in the case of glassy carbon[23a] and gold substrates. However, the relatively high uncertainty associated with the ellipsometry measurements may simply be the cause of this discrepancy.…”

“…At the same time the expected correlation between the bromine and brush contents for Ni‐Gra‐Br Y and Ni‐Gra‐PMMA Y , respectively, would then ensue in accordance with our previous studies on the growth of PMMA brushes on glassy carbon and gold. [23a,]…”

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

“…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. In most cases, 4-(2-hydroxyethyl) benzene diazonium, synthetized from the corresponding commercial aniline precursor, is used to prepare a reactive platform with hydroxyethyl functionalities inducing addition-elimination reaction on an acyl bromide (bromopropionyl bromide 182 or 2-bromoisobutyryl bromide [218][219][220][221] ). The second postfunctionalization option considered is based on the formation of a carboxyphenyl platform on which the initiator is immobilized via a one-step 222 or a three-step 90 procedure.…”