Association behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers with cationic surfactants in aqueous solution.

The association behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers in aqueous solution with hexadecyltrimethylammonium bromide (HTAB), tetradecyltrimethylammonium bromide (TTAB), and dimethylene bis(decyldimethylammonium bromide) (10-2-10), was studied by fluorescence, viscosity, and Krafft temperature measurements. It has been observed that (EO)18(PO)31(EO)18 interacts more strongly than (EO)2(PO)15.5(EO)2 and (EO)2.5(PO)31(EO)2.5 with HTAB/TTAB due to synergistic interactions. A stronger capability of (EO)18(PO)31(EO)18 to interact with cationic surfactants arises from the greater number of electronegative EO units (total 36 EO units) than of (EO)2(PO)15.5(EO)2 (total 4 EO units) and (EO)2.5(PO)31(EO)2.5 (total 5 EO units). The antagonistic mixing behavior of present triblock polymers has been observed with 10-2-10. A difference in the mixing behavior of the latter from that of HTAB/TTAB has been attributed to its dimeric nature, which may create steric hindrances with triblock polymer components at the head group region in the mixed state.