The association properties of block copolymers of ethylene oxide (E) and 1,2-butylene oxide (B) manufactured by The Dow Chemical Company were studied by static and dynamic light scattering, The critical micelle concentrations and micelle association numbers so obtained were combined with literature values for related copolymers in order to discuss the effect of block architecture on the association properties of linear diblock and triblock copolymers. The measurements significantly increase the available data for E(m)B(n)E(m) triblock copolymers and provide new insight into effects caused by E-block distributions originating from the different rates of reaction of ethylene oxide with primary and secondary oxyanions during copolymerization.