Synthesis, Characterization, and Interfacial Behaviors of Poly(oxyethylene)-Grafted SEBS Copolymers

Poly(oxyalkylene) blocks (POA) were synthetically grafted onto polystyrene-b-poly(ethylene/butylene)-b-polystyrene (SEBS) by the reaction of the maleated SEBS and various poly(oxyalkylene)amines. Structurally, the prepared comb-branch copolymers consist of a hydrophobic SEBS triblock backbone (approximate 45 000 MW with ∼29 wt % of styrene content) and multiple poly(oxyethylene) (POE) or poly(oxypropylene) (POP) pendants (in the range of 2000−6000 MW for each pendant). The hydrophilicity was probed by measuring the polymer surface resistivity from 1011.4 to 108.1 Ω/sq, depending on the pendant structures. In toluene or hexane, these copolymers formed very stable multiple emulsions with water as observed by an optical microscope. The copolymers were capable of reducing interfacial tension of toluene/water, in one example, from 31 to 7.4 dyn/cm by adding the copolymer at 3 × 10-2 g/100 mL concentration. At very low concentration (3 × 10-4 g/100 mL), these copolymers exhibited high efficiency in reducing interfacial tensions up to 17.5 dyn/cm, but slowly reaching the equilibrium over a 10-h period. In comparison, the commercially available Span 60 surfactant (HLB = 4.7) at the same concentration can only reduce to 28.5 dyn/cm. These phenomena are rationalized by the collective noncovalent bond interactions, predominantly the π−π interaction of the polystyrene block with toluene and the hydrogen bonding of the POE segments with water molecules.