Interpolymer complexes of poly(methacrylic acid) and poly(2-alkyl-2-oxazolines): pH-mediated assembly, quantum-chemical insights into hydrogen-bond structure, and iodine vapour sorption

The pH-mediated assembly of hydrogen-bonded interpolymer complexes between poly(methacrylic acid) and poly(2-alkyl-2-oxazolines) was investigated in aqueous solutions. Critical pHs (pH crit ) of complexation were determined across a range of polymer concentrations. The pH crit shifted to higher values with the formation of interpolymer complexes moving from poly(2-methyl-2-oxazoline) to poly(2-ethyl-2-oxazoline) and poly(2-n-propyl-2-oxazoline), reflecting changes in hydrophilic-hydrophobic balance. Geometry optimisation and electronic structure calculations of the hydrogen bonding in the interpolymer complexes were performed using the quantum-chemical DFTB method with 3ob-3-1 parameters and the Grimme D3(BJ) dispersion correction. These calculations revealed that the most energetically favourable hydrogen bond structure involves the carbonyl oxygen of poly(2-alkyl-2-oxazoline) forming a bond with the hydrogen of the protonated carboxylic group of poly(methacrylic acid). Infrared spectroscopy and thermal analyses of these interpolymer complexes in the solid state were performed and show the presence of interactions between the polymers. The sorption of iodine vapours by the interpolymer complexes, as well as by the individual polymers, was investigated. It was found that poly(methacrylic acid) exhibits poor iodine sorption, whereas poly(2-alkyl-2-oxazolines) demonstrate a strong affinity for iodine. Complexation with poly(methacrylic acid) significantly reduces the ability of poly(2-alkyl-2-oxazolines) to sorb iodine vapours. • Interpolymer complexes of PMAA and poly(2-alkyl-2-oxazolines) were studied in water. • The critical pH of complexation increases with poly(2-alkyl-2-oxazoline) hydrophobicity. • DFTB calculations indicate preferential hydrogen bonding via the amide carbonyl oxygen. • Infrared spectroscopy and thermal analysis confirm the formation of distinct complexes. • Iodine vapour sorption indicates reduced functional group accessibility upon complexation.