Association of hydrophobically end-capped poly(ethylene oxide).: 1.: Preparation of polymers and characterization of critical association concentrations

A series of poly(ethylene oxide)s (PEO)s, end-capped with hydrophobic groups, were prepared via various methods and characterized by H-1 NMR, UV spectroscopy and size exclusion chromatography. Fully and partially modified difunctional and monofunctional samples were studied. Critical association concentrations (CAC)s were measured, by fluorometry in the presence of pyrene, as a function of PEO chain length and aliphatic chain ends for fully modified samples. It was found that variations in CACs of monofunctionalized PEOs could be well understood through theoretical approaches that took into account the repulsion between PEO chains that hindered micelle formation. Even though theory predicted considerably lower values for difunctionalized samples (with the same ratio of hydrophilic to hydrophobic units) their CAC values were found, however, to be very close to those of monofunctionalized PEOs of equivalent molecular weights. CACs were also measured for partially modified samples, and variations in CAC with degree of functionalization were found to be surprisingly small. The values of CACs obtained were compared to another critical concentration, C-eta, at which point viscosity diverges from that of parent PEOs.