Solution Properties of Phosphorylcholine-Based Hydrophobically Modified Polybetaines in Water and Mixed Solvents

Abstract

Fluorescently labeled amphiphilic polybetaines have been prepared, and their dilute solution properties in water, chloroform, methanol, and mixed organic solvents have been investigated by fluorescence spectroscopy, dynamic light scattering, and 1H NMR spectroscopy. The copolymer chains consisted of N-isopropylacrylamide and N-phosphorylcholine-N‘-ethylenedioxybis(ethyl)acrylamide units in ∼1/1 molar ratio, as well as from 3 to 10 mol % hydrophobic units, such as N-n-(octadecyl)acrylamide, N-(1H,1H-perfluoro-n-octyl)acrylamide, or N-[(1-pyrenyl)-4-butyl]-N-(n-octadecyl)acrylamide. In water, the polybetaines associate in multichain aggregates ranging in size from 170 to 220 nm. The assembly of the polymers in water is triggered by two cumulative effects: (1) hydrophobic interactions between the hydrocarbon or fluorocarbon chains and (2) ion pair formation between the phosphorylcholine groups. The polymers do not associate in methanol, but chain aggregation occurs in chloroform, where the phosphorylcholine...