Sphere to rod transition of micelles formed by amphiphilic diblock copolymers of vinyl ethers in aqueous solution

Amphiphilic block copolymers of vinyl ethers containing a-hydroxyethyl viny l ether (HOVE) and partially deuterated n-butyl vinyl ether (NBVE) were syn thesized by living cationic polymerization. Four block copolymers with the same hydrophilic length but different hydrophobic lengths were prepared. Th e internal structures of the micelles formed by these copolymers in aqueous solution were investigated by the contrast variation method of small-angle neutron scattering (SANS) measurement. The molar volume of HOVE was estima ted to be quite small from the dependence of the forward scattering intensi ty on the contrast, which comes from the hydration effect in the micellar s hell. The SANS data were well. described by the theoretical form factor of a core-shell model. The micellar shape was strongly dependent on the hydrop hobic chain length of the block copolymer. The polymer with the shortest hy drophobic chain was suggested to form spherical micelles, whereas the scatt ering curves of the longer hydrophobic chain polymers showed the q(-1) depe ndence, reflecting the formation of rodlike micelles. These scattering curv es could be described well by a sphere-rod coexistence model. The volume fr action of the rodlike micelle was found to increase with increasing hydroph obic chain length.