Characterization of Oligo(ethylene glycol) and Oligoglycerol functionalized Poly(ether imide) by Angle-dependent X-ray Photoelectron Spectroscopy


Purpose: Previous investigations have shown that poly(ether imide) (PEI) membranes can be functionalized with aminated macromolecules. In this study we explored whether the characterization of PEI functionalized with oligo(ethylene glycol) (OEG) or linear, side chain methylated oligoglycerols (OGMe), by angle-dependent X-ray induced photoelectron spectroscopy (XPS) can be used to prove the functionalization, give insight into the reaction mechanism and reveal the spatial distribution of the grafts. 
Methods: PEI membranes were functionalized under alkaline conditions using an aqueous solution with 2 wt% of α-amino-ω-methoxy oligo(ethylene glycol) (Mn = 1,320 g·mol-1) or linear, side chain methylated monoamine oligoglycerols (Mn = 1,120, 1,800 or 2,270 g·mol-1), respectively. The functionalized membranes were investigated using XPS measurements at different detector angles to enable comparison between the signals related to the bulk and surface volume and were compared with untreated and alkaline-treated PEI membranes.
 Results: While at a perpendicular detector angle the bulk signals of the PEI were prominent, at larger surface volume-related detector angles, the signals for OGMe and OEG were determinable. 
Conclusion: The surface functionalization of PEI with OEG and OGMe could be verified by the angle-dependent XPS. The observations proved the functionalization at the PEI surface, as the polyethers were detected at angles providing signals of the surface volume. Furthermore, the chemical functions determined verified a covalent binding via the nucleophilic addition of the amine functionalized OGMe and OEG to the PEI imide function.
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