Unicore-Multicore Transition of the Micelle Formed by an Amphiphilic Alternating Copolymer in Aqueous Media by Changing Molecular Weight

Aggregates formed from amphiphilic alternating copolymer samples of sodium maleate and dodecyl vinyl ether (MAL/C12) of different molecular weights or (weight-average) degrees of polymerization N(w1) (= 76-5000) were characterized by light scattering and fluorescence techniques in 0.05 M aqueous NaCl at pH 10 to investigate the molecular weight dependence of the micellar structure of amphiphilic polyelectrolytes. The light scattering and fluorescence data demonstrated a unicore-multicore transition of the MAL/C12 micelle at N(w1) approximate to 300. The structures of unicore and multicore micelles of MAL/C12 copolymers formed were analyzed using the flower micelle model and the flower necklace model, respectively. The data points for unicore: micelles formed from the three low-molecular-weight MAL/C12 fractions were in good agreement with the flower micelle model of the minimum loop size determined by the rigidity of the polymer main chain, which we proposed previously [Kawata et al. Macromolecules 2007, 40, 1174-1180]. On the other hand, the data points for the four high-molecular-weight MAL/C12 fractions were nicely fitted to the flower necklace model, the conformation of which was represented as the touched bead model.