MICELLIZATION OF STRONGLY SEGREGATED BLOCK-COPOLYMERS

Series of diblock copolymers of the type poly(styrene-b-4-vinylpyridin e) (PS-P4VP) are synthesized via anionic polymerization. In toluene, a selective solvent for the PS block, well-defined micelles with narrow molecular weight distribution are formed. Size and shape of the micel les are characterized by static (SLS) and dynamic light scattering (DL S), and electron microscopy (EM). The aggregation number Z exhibits a scaling relation 7 proportional to (NP4VPNPS-0.79)-N-1.93, where N is the degree of polymerization of each block. We find this behavior clos e to a Z similar to (NANB-0.8)-N-2 limiting scaling law which appears to be a characteristic of strongly segregated diblock and triblock cop olymer systems as well as low molecular weight cationic, anionic, and nonionic surfactants. A simple micellization model is developed that p redicts aggregation;numbers of surfactants, diblock, triblock, and gra ft copolymers. The corona dimension D-h as measured by DLS scales as D -h proportional to Z(0.21)N(PS)(0.63) in agreement with the theoretica l prediction D similar to Z(1/5)N(B)(3/5) for starlike molecules in go od solvents. Neither unimers nor a critical micelle concentration are observed. Instead at very low concentrations the excess scattering int ensity increases due to the formation of large particles. (C) 1996 Ame rican Institute of Physics.