ASSOCIATION PROPERTIES OF A TRIBLOCK COPOLYMER OF ETHYLENE-OXIDE AND STYRENE OXIDE, S4E45S4, IN AQUEOUS-SOLUTION

The block copolymer S4E45S4 has been prepared by sequential anionic co polymerisation of ethylene oxide followed by styrene oxide starting fr om a difunctional initiator. The notation E denotes an oxyethylene uni t and S an oxyphenylethylene unit. Clouding of aqueous solutions was s tudied across the concentration range 0.01-40 wt.%. Micellar propertie s were investigated by static and dynamic light scattering: at 15 degr ees C the mass-average association number of the micelles was 24. Seco nd virial coefficients, from both static and dynamic light scattering, were found to be negative, consistent with significant micellar linki ng. The critical micelle concentration (c.m.c.) of the copolymer in so lution at 15 degrees C was very low, ca. 0.013 g dm(-3). Comparison of this c.m.c. with published values for BnEmBn triblock copolymers (B = oxybutylene) shows the hydrophobicity of an S unit to be three times that of a B unit. Extension of the comparison to oxyethylene-oxypropyl ene (E-P) block copolymers leads to the scale of hydrophobicities S:B: P = 12:4:1.