Polymer Brushes by Grafting to Reaction in Melt: New Insights into the Mechanism

Abstract

tethered polymers, generally indicated as polymer brushes, have gained great interest for their ability to modify the surface interaction with the surrounding environment. One of the most common strategies to obtain polymer brushes is based on the reaction of end-functional polymers with the substrate surface, in a process defined as grafting to. The two advantages of grafting to reactions are i) the functional polymer is prepared before the grafting reaction and therefore can be fully characterized and ii) the reaction has a self-limiting nature, meaning that the number of grafted chains converges to a plateau value after a sufficiently long reaction time. The limit value of grafted chains is governed by the molecular weight of the employed polymer, thus allowing a fine control of the brush thickness. In this work, the origin of the self-limiting nature of the grafting to reaction is discussed comparing theoretical models with experimental data. Furthermore, the kinetics of the process is discussed, considering both polymer diffusion and end-group reactivity as the main drivers of the grafting to process. Finally, the effect of molecular weight dispersity on the brush characteristics is highlighted.

Modular and Substrate-Independent Grafting-To Procedure for Functional Polymer Coatings

“…2,5 Yet, this limitation does also provide the ability to control grafting densities of the produced polymer brush coating by variation of the size of the grafted polymer chains, with higher grafting densities obtained for shorter polymers and vice versa. 5,6 Evidently, irrespective of the employed grafting approach, the chemical and physical characteristics of the target substrate vary significantly for different materials. Due to these characteristics, the synthesis procedures for polymer brush coatings are typically substrate-dependent and cannot be applied modularly.…”

“…In contrast, the grafting-to approach allows straightforward analysis of the polymers before attachment to the surface. , For the grafting-to approach, however, excluded-volume interactions of the polymers during the grafting step limit the number of chains that can be attached on the surface . As a result, grafting densities and layer thicknesses of polymer brushes produced via grafting-to are typically significantly lower than those produced via grafting-from. , Yet, this limitation does also provide the ability to control grafting densities of the produced polymer brush coating by variation of the size of the grafted polymer chains, with higher grafting densities obtained for shorter polymers and vice versa . , …”