Supramolecular self-assembly of a polyelectrolyte chain based on step-growth polymerization of hydrophobic and hydrophilic monomers

A novel amphiphilic polyelectrolyte (APE) prepared by step growth polymerization of hydrophobic and hydrophilic monomers is shown to have self-assembly structures. The polymerization reaction between citric acid and hexamethylene diisocyanate led to poly(hexamethylene citramide imide) (PHMCI), which was characterized by two-dimensional NMR, vibrational spectroscopies and gel permeation chromatography. Hydrolysis of PHMCI through a ring opening reaction resulted in a polyelectrolyte, poly(hexamethylene citramide) (PHMC) with three key elements of self-organization, i.e., ionizable side chains, hydrophobic groups and hydrogen bonding. PHMC is able to self-assemble to nanoparticles in water with variable hydrodynamic diameters and surface structures. The presence of noncovalent cross-linking of cooperative H-bonding units facilitates the formation of the polymer nanoparticles. The cooperative H-bonding is maintained from pH 5.5 to 10.0, which is verified by quantum chemical calculations. The nanoparticles are highly efficient metal chelators, offering potential as new remedies for metal sequestration in water or soil.