Micelle properties of a dimethylamino- and a trimethylammonium-tipped oxyethylene–oxybutylene diblock copolymer in water

Abstract

Micelle properties in aqueous solution at temperatures in the range 20–50 °C of Me₂N(CH₂)₂OE₄₉B₉ and I⁻Me₃N⁺(CH₂)₂OE₄₉B₉, where E represents an oxyethylene unit and B an oxybutylene unit, have been investigated by dynamic and static light scattering, and the results compared with results for E_mB_n copolymers. For micelles of the dimethylamino-tipped copolymer in aqueous solution, the hydrodynamic radius, r_h, was large relative to the thermodynamic radius, r_t, suggesting a “soft” micelle. For the trimethylammonium-tipped copolymer, r_h decreased and r_t increased with increase in temperature, and values of association number, N_w, were low, but increased with increase in temperature, indicating a change from soft micelles at low temperature to small, less swollen micelles at high temperature. High values of thermodynamic volume per molecule, ν_t/N_w, for the polymer with the charged tip could be attributed to intramicellar charge effects. Addition of salt, to screen the charges, led to a decrease in ν_t/N_w and an increase in r_h, r_t and N_w.