Azobenzene-Based Poly(ether-ketone)s with tunable alkylene spacers: synthesis, morphological, thermal characterization, and efficient dye adsorption

Abstract

A series of novel Poly(ether-ketone)s (PEK-6, PEK-8, and PEK-10) were successfully synthesized via a Friedel–Crafts polyacylation reaction using bisphenoxyalkane-based monomers with varying methylene spacer lengths (m = 6, 8, 10) and azobenzene-4,4’-dicarbonyl dichloride as the comonomer. The chemical structures of the monomers were confirmed by ¹H-NMR, ¹³C-NMR, FTIR, and mass spectrometry, while the polymers were characterized by FTIR, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction (XRD). FTIR spectra confirmed the successful incorporation of carbonyl and ether groups into the polymer backbone. TGA analysis revealed that all polymers exhibited good thermal stability, though PEK-10 showed a lower onset degradation (T_d5 = 195 °C) compared to PEK-6 and PEK-8 (both with T_d5 = 307 °C). SEM images indicated significant morphological differences among the samples, with surface roughness increasing with longer alkyl chains. XRD analysis showed a predominantly amorphous nature. The dye adsorption potential of the synthesized PEKs was explored using methylene blue as a model dye. Time-dependent UV–Vis spectroscopic studies indicated significant differences in adsorption behavior between the polymers. PEK-10 exhibited excellent and sustained adsorption performance, with absorbance decreasing from 0.56 to 0.09 at 664 nm after 24 h, highlighting strong dye-polymer interaction and retention. In contrast, PEK-8 initially showed rapid adsorption (to 0.35 in 10 min) but was followed by gradual desorption over time, returning to 0.55 after 24 h. These findings underscore the impact of alkyl spacer length on the structural, thermal, and adsorption properties of PEKs and suggest PEK-10 as a promising candidate in environmental remediation, particularly for dye removal from aqueous systems.