REGULAR STAR POLYMERS WITH 64 AND 128 ARMS - MODELS FOR POLYMERIC MICELLES

Carbosilane dendrimers with 64 and 128 surface Si-Cl bonds were used as coupling reagents for monodisperse poly(butadienyl)lithium. Two series of regular star polybutadienes with 64 and 128 arms were prepared. The arm molecular weight was varied between 6400 and 72000. The dilute-solution properties of the stars were determined in a good solvent (cyclohexane) and in a theta-solvent (dioxane) for polybutadiene. Measurements of R(G), A2, D0, and [eta] indicate that the isolated stars behave as hard spheres. The ratio of the hydrodynamic radius over the radius of gyration is slightly larger than (5/3)1/2. In a comparison which includes previously made stars with lower functionality, it is found that g = [R(G2)]/[R(G2)]lim is-proportional-to f-0.73 in the good solvent and f-0.64 in the theta-solvent. The former result is in good agreement with the Daoud-Cotton scaling model of stars. The latter dependence is stronger than the theory predicts: g(theta) is-proportional-to f-0.5. A recent quantitative model developed by Gast et al. for polymeric micelles is in good agreement with the present experimental data. Stars with many arms represent good model polymers for polymeric micelles.