Association Properties of a Diblock Copolymer of Ethylene Oxide and Styrene Oxide in Aqueous Solution Studied by Light Scattering and Rheometry

Copolymer S13E60 (E = oxyethylene unit, S = oxyphenylethylene unit) was synthesised and characterised by gel permeation chromatography (for distribution width) and 13C NMR spectroscopy (for absolute molar mass and composition). Dynamic and static light scattering were used to determine micellar properties in dilute aqueous solution at three temperatures (20, 30 and 40°C): i. e. association number, hydrodynamic and thermodynamic radii. Comparison with reported results for related copolymers allowed exploration of the dependence of these properties on hydrophobe block length. The phase behaviour of the copolymer in aqueous solution was defined using tube inversion and rheometry (for yield stress and dynamic modulus). The hard-gel boundary was detected by both methods in satisfactory agreement. Discussion is focused on effects of micelle stability on the shape and extent of the hard-gel region of the phase diagram. A region of soft gel was detected at low concentrations by rheometry, and assigned to a percolation mechanism.