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 male ated SEES and various poly(oxyalkylene)amines. Structurally, the prepared c omb-branch copolymers consist of a hydrophobic SEES triblock backbone (appr oximate 45 000 MW; with similar to 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 measur ing the polymer surface resistivity from 10(11.4) to 10(8.1) Omega/sq, depe nding on the pendant structures. In toluene or hexane, these copolymers for med very stable multiple emulsions with water as observed by an optical mic roscope. The copolymers were capable of reducing interfacial tension of tol uene/water, in one example, from 31 to 7.4 dyn/cm by adding the copolymer a t 3 x 10(-2) g/100 mt concentration. At very low concentration (3 x 10(-4) g/100 mt), these copolymers exhibited high efficiency in reducing interfaci al tensions up to 17.5 dyn/cm, but slowly reaching the equilibrium over a 1 0-h period. In comparison, the commercially available Span 60 surfactant (H LB = 4.7) at the same concentration can only reduce to 28.5 dyn/cm. These p henomena are rationalized by the collective noncovalent bond interactions, predominantly the pi-pi interaction of the polystyrene block with toluene a nd the hydrogen bonding of the POE segments with water molecules.