pMAIRS Analysis on Chain-End Functionalization of Densely Grafted, Concentrated Polymer Brushes

Abstract

The degree of chain-end functionality in a densely grafted, concentrated polymer brush is a critical parameter. In this study, p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) technique was applied to monitor the emergence and disappearance of substituted azide (N3) at the chain ends of polymer brushes, allowing the accurate determination of the azide density and the click reaction efficacy. The peak separation of the N3 absorption bands in the pMAIRS spectra showed that azide substitution occurred not only at the brush ends but also at the underlying initiators that did not react during surface-initiated atom transfer radical polymerization. Hence, the density of each type of azide group and the efficiencies of the azidation and click reaction could successfully be estimated. Furthermore, a chain-end-selective click reaction was demonstrated for the azide-functionalized polymethacrylate-type polymer brushes based on size exclusion effects and polarity differences. Thus, the pMAIRS method provides important quantitative information that can expand the applications of chain-end functionalized polymer brushes.

Progress on highly proton-conductive polymer thin films with organized structure and molecularly oriented structure

“…Our group reported the highly oriented structure of Nafion thin films on SiO x [34], MgO [35,36], sputtered Pt [37], and sputtered Au [36] surfaces by infrared p-polarized multiple-angle incidence resolution spectrometry (pMAIRS), which was developed by Hasegawa and co-workers [38][39][40], as presented in Figure 2(a-d). IR pMAIRS offers the molecular orientation for each functional group to various functional materials such as derivatives of polythiophene [41,42], porphyrin [43], pentacene [44], fullerene [45], naphthalene diimide [46], phthalimide [47], azulene [48], metal-oxide nanowire [49], polymer brushes [50], and polyimide [51]. Because this spectroscopic method is an infrared spectroscopic method, it is useful because it is applicable to non-crystalline materials.…”

A guide to functionalisation and bioconjugation strategies to surface-initiated polymer brushes

“…Poly(styrene) (PS) brushes displayed the same tendency with lower end-chain azide fucntionalization with thicker brushes, but this was not the case for PMMA brushes, where the thickness was not found to influence the ultimate end-chain conversion. 100 The cycloaddition of an azide and alkyne has also broadly been applied to the end-chain functionalisation of polymer brushes, making use of the simplicity of conversion of halides to azides (although approaches to develop azide or alkyne-end functionalised brushes from RAFT have also been proposed). Whilst non-strained alkynes require catalysis by copper(I) complexes, strained alkynes, such as those present in cyclo-octyne, can proceed rapidly, without any catalysis, enabling to broaden the range of applications of these reactions.…”

“…However, these strained alkynes are relatively bulky and hydrophobic, which may affect the physico-chemical properties of the brush. This strategy has nonetheless been applied to the functionalisation of POEGMA, 118,121,137 PDEGMA, 83 PNIPAM, 140 PMMA 81,100 and PS 100 brushes end-terminated with azido functions, enabling a simple and efficient route to tether functional molecules, from dyes to biotin residues (Fig. 8).…”

“…Ensuring a tight control of the polymerisation is crucial, in order to ensure fidelity of bromine ends and high functional densities. 100 In contrast, if termination of the living chains is desired, nucleophilic substitution of the halide end can be performed, for example, with NCB as a capping agent. 101 In another example, PDEGMA brushes were functionalized with azides for coupling of BODIPY-alkyne dyes via Huisgen 1,3-dipolar cycloaddition.…”

Chain End-Functionalized Dense Polymer Brushes from an Inimer Coating by SI-RAFT

“…Modification of surfaces with polymer brushes is a useful strategy to tune the properties of the surface, such as wetting, adhesion, catalytic, electronic, or biological activity. − The term “polymer brush” is used to encompass a wide class of materials in which polymers are tethered at one chain end to a surface, leading to coatings with high mechanical stability through subsequent processing steps . Both the conformation of the polymer brush and the functionality at the untethered chain end are important for tuning the nature of the interactions of the brush with the outside world. ,− Conformational changes in polymer brushes can occur in response to stimuli such as solvent, temperature, and pH that cause the brush to swell or collapse . These conformational changes have shown promise in several applications.…”