Synthesis and characterization of copolyethersulfones with pendant carboxylic groups

Polyethersulfone based copolymers containing different percentages of 4,4'-bis(4-hydroxyphenyl)pentanoic acid (DPA) were synthesized and investigated in order to prepare membranes for removing heavy metals. The copolymers obtained contain 10, 20, 30, 50, 70% mol of DPA and were prepared by nucleophilic polycondensation reaction between DPA and 4,4'-sulfonyldiphenol (DHDPS) with 4,4'-dichlorodiphenyl sulfone (DCDPS). Chemical properties and thermal stability have been studied with particular attention to the influence of the diphenolic acid moiety on the polyethersufone. The functional carboxylic group of the DPA unit of the PES-DPA copolymers was also used for the insertion of telechelic oligomers of polyethersulfone sulphonated (S-PES) with controlled degree of polymerization to synthesize grafted sulfonated copolymers with a comb structure and improved properties in terms of proton conductivity. The proposed idea is to develop filtration membranes with selective properties against heavy metal ions; preliminary tests were carried out in aqueous solutions containing known percentages of heavy metals (Pb, Cr, Cu, Cd, Zn, V). Copolymers were characterized by 1H-NMR spectrometry, MALDI-TOF mass spectrometry, FT-IR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The chemical-structural characterization by 1H-NMR and MALDI-TOF MS analysis confirms the formation of macromolecular chains terminated with OH and Cl functional groups. TGA analysis shows high thermal stability of the polymers, higher in the samples containing lower percentages of DPA. Preliminary studies revealed the ability of PES-DPA copolymers to adsorb some heavy metals in a selective manner, expecially Cr and Pb in aqueous solution