Association and surface properties of tapered statistical copolymers of ethylene oxide and butylene oxide in water

Two statistical copolymers of ethylene oxide (EO) and 1,2-butylene oxide (BO) of different compositions (80 and 60 mol% oxyethylene) were polymerised (anionic polymerisation with monofunctional initiation) to 100% conversion. Their molar masses (Mn ≈ 5000 g mol-1) and molar mass distributions (Mw/Mn ≈ 1.06) were similar. The disparity in reactivity ratios in the EO/BO copolymerisation resulted in pronounced composition drift along the chains (tapered statistical copolymers) giving them the character of diblock copolymers. The association behaviour of the copolymers in aqueous solution at 25°C was studied by dynamic and static light scattering and surface tension. It was confirmed that both formed micelles by a closed process. Surface activity, as measured by surface tension lowering, was superior to conventional EO/BO diblock copolymers with comparable micelle properties. Phase diagrams, determined over a wide concentration range (c ≤ 70 wt.%), showed regions of gel formation (liquid crystallinity) and clouding (phase separation).