Characterization of micellization behavior of amphiphilic polymer having octadecyl group by small angle X-ray and neutron scattering

Amphiphilic diblock polymers having an octadecyl group as a hydrophobic seg ment with different degrees of polymerization were synthesized by living ca tionic polymerization. Matrix-assisted laser desorption-ionization time-of- flight mass spectrometry (MALDI TOF MS) was performed to determine the mole cular weight. Differential scanning calorimetry (DSC) measurements for poly mer solid samples showed the melting point depending on the degree of polym erization. The size and shape of micelles formed by the polymers in water w ere investigated by small-angle X-ray scattering (SAXS) and neutron scatter ing (SANS) measurements. The aggregation number reduced with increasing deg ree of polymerization, while the overall micelle size was almost independen t. The SAXS and SANS data revealed the sphere-to-disk transition on changin g temperature for the polymer with the shortest hydrophilic chain. Below th e melting point of hydrophobic chain, the polymer formed disklike aggregate s with a crystallized core of octadecyl groups surrounded by a swollen shel l. With increasing temperature, octadecyl groups melted and the spherical m icelle formed.