Hybrid copper-polyelectrolyte nanoaggregates obtained with smart block copolymers based on 4-[(hydroxyimino)aldehyde]butyl methacrylate (HIABMA) in water and acetonitrile

Abstract

The AB multi-stimuli-responsive block copolymer pTEGMA-b-pHIABMA (TEGMA: tetra(ethyleneglycol) methyl ether methacrylate; HIABMA: 4-[(hydroxyimino)aldehyde]butyl methacrylate) comprises a hydrophilic and thermoresponsive PTEGMA block linked to the hydrophobic PHIABMA chain. The latter is endowed with slightly acidic oxime groups that potentially form complexes with metal ions. Here we investigate the formation of hybrid Cu(II)-polymer nanoaggregates both in water and in acetonitrile. Cu(II) ions are quantitatively and rapidly incorporated, in the presence of a base, into pre-formed polymeric core-shell micelles (30 nm diameter by DLS) in water up to 1:2 metal-to-ligand stoichiometry. The pKa of the polymer is decreased from ≅11.2 to 4.65 due to interaction with Cu(II) and the complex is shown to involve oximate ions. The thermoresponsivity of the polymeric micelles remains unchanged with Cu(II) complexation and allows an easy separation by flocculation of the hybrid complex. Moreover, nanoaggregates (D = 20 nm) form in acetonitrile from the fully solubilized copolymer interacting with Cu(OAc)2. The 1:2 Cu(II)/ligand stoichiometry is confirmed with the Job graphical method. Characterization of the hybrid micelles was carried out by UV–Vis spectrometry, DLS, TEM, STEM and SAXS. Quantitative release of Cu(II) in acidic conditions is demonstrated both in water and in acetonitrile. Full recovery of the free metal ions and of intact polymeric micelles is achieved through centrifugal filtration of the aqueous preparation, as a proof-of-concept for a recyclable system for metal uptake and release. Furthermore, Cu0 nanoparticles of 5–10 nm are obtained through reduction of Cu(II) within the micelles with ascorbic acid in aqueous solution.