MICELLIZATION AND MICELLAR STRUCTURE OF A POLY(ETHYLENEOXIDE) POLY(PROPYLENEOXIDE)/POLY(ETHYLENEOXIDE) TRIBLOCK COPOLYMER IN WATER SOLUTION, AS STUDIED BY THE SPIN-PROBE TECHNIQUE/

The micellization of the triblock copolymer Pluronic P85 (27)/poly(oxy propylene)(39)/poly(oxyethylene)(27)) in aqueous solution was followed us temperature and addition of aliphatic alcohols, using the spin pro be technique. Different types of probes properly chosen (spin-labeled (SL) poly(oxyethylene(4))nonylphenol, SL-Pluronic L62, TEMPO-laurate, TEMPO-hexanoate, CAT 4, CAT 8, CAT 11, CAT 16, and 5-, 7-, 10-, and 12 -doxylstearic acids) provided information about the micellar structure (polarity, viscosity, and order degree) at different radial locations . Micellization was found to be low at room temperature, even for 10% aqueous solutions, but strongly increasing with temperature increase t o about 323 K. Hydration of the poly(oxyethylene) (PEG) chains in the shell was found to diminish toward the interior and with increasing te mperature. At an intermediate region of the shell, a hydration number ([H2O]/EO unit) close to 3 was found at 293 K, which decreased to simi lar to 1 at 323 K. No hydration was found in a region corresponding to 4-6 EO units from the core. At the PPO/PEO interface, a further decre ase in polarity occurred in the 323-373 K temperature range, probably due to an extension of the hydrophobic core-with increasing temperatur e, with prevalence of the nonpolar conformations of the PPO and PEO ch ains. At 323 K, the order degree of the PEO chains decreased rapidly t oward the interior of the shell. Addition of medium chain aliphatic al cohols to the aqueous solution of the polymer substantially enhanced m icellization at room temperature. The effect increased with the alcoho l chain lenght in the C-4-C-6 series. The addition of alcohols (Cs, Ca ) was found to have similar effects with temperature increase, i.e., t o promote micellization and to reduce the hydration and the order degr ee in the shell. In both cases the effects are due to an increased hyd rophobe character of the core.