Micellization of poly(oxyethylene-6-oxypropylene-6-oxyethylene) triblock copolymers (Pluronic polymers F68, P85, and F108) in aqueous solutions was studied, and critical micellization concentrations (cmc) were determined using surface tension measurements and fluorescent probes (pyrene, l,6-diphenyl-l,3,5-hexatriene). The dependence of cmc on temperature was observed, and critical micellization temperatures characterizing temperature-dependent transitions of Pluronic unimers to multimolecular micelles were measured. The molecular characteristics of P85 and F108 micelles including their dimensions, molecular masses and surfactant aggregation numbers were determined using lightscattering and ultracentrifugation techniques. Depending on the type of Pluronic, the micelles had an average hydrodynamic diameter ranging from about 15 to about 35 nm, a molecular mass of about 200 kDa and aggregation numbers ranging from one to several dozens. The partitioning of fluorescent probes between aqueous and micellar phases was analyzed within the frame of a pseudophase model, and the partitioning coefficients were determined using the fluorescence data. The results are compared with previous reports and are discussed in relationship to the application of block copolymer micelles as microcontainers for drug delivery.

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The interaction of α-chymotrypsin covalently bound to quaternized poly(4-vinylpyridine) with oppositely charged latex particles was investigated and compared with that of free a-chymotrypsin. The free enzyme and the corresponding polymer conjugates were added to a mixture of two latexes: one coated with bovine serum albumin and the other with specific inhibitor of a- chymotrypsin. The polycations themselves were found to be nonselectively adsorbed on oppositely charged latex surfaces. However, the ca-chymotrypsin-polycation conjugates, as well as the free enzyme, were selectively adsorbed on the latex surfaces coated with the enzyme inhibitor. The results are considered to mimic the search and recognition mechanism for target cells by polyelectrolytes carrying a specific vector moiety.