Association Properties of Diblock Copolymers of Propylene Oxide and Ethylene Oxide in Aqueous Solution. The Effect of P and E Block Lengths

Abstract

Three diblock copolymers of propylene oxide and ethylene oxide were prepared by sequential oxyanionic
polymerization; P94E316, P60E348, and P43E312. Light scattering and dye solubilization were used to confirm
micellization in dilute aqueous solution and to determine the temperature dependence of the critical
micelle concentration (cmc), and eluent gel permeation chromatography was used to determine the extent
of micellization. Comparison with results for the series of copolymers EmPn (m ) 98-104, n ) 37-73,
published previously) shows that values of the cmc in molar units depend almost entirely on P-block length,
i.e., that the effect of E-block length on critical micelle concentration is insignificant in the range m )
100-300. Light scattering was also used to determine micellar association numbers (Nw) and radii. Present
and previous values of Nw fit well to a scaling law for block lengths (P and E) similar to that proposed by
Nagarajan and Ganesh for EmPn copolymers. Gel boundaries were determined by a tube-inversion method,
and critical gel concentrations were found to coincide with values predicted by using micellar parameters
determined by static light scattering.