CONCENTRATION-DEPENDENCE OF THE RELATIVE VISCOSITY OF STAR POLYMERS

The concentration dependence of the relative viscosities of polybutadi ene star polymers with 64, 128 and 270 arms has been investigated in t he good solvent toluene. It is shown that the viscosity-concentration behavior of these stars matches that of hard-sphere suspensions. Near the overlap concentration c, the star polymers form physical gels sim ilar to the behavior of hard-spheres at the close packing volume fract ion. Blending of two 128-arm stars with a large differences in size re duces the viscosity of the solutions and delays the gel formation to h igher concentration. A sufficiently high segment density in the outer corona of the polymer coils is required in order to observe the hard-s phere viscosity-concentration profiles as demonstrated by the results on 32-arm stars and fuzzy 64-arm stars with 32-arms in the corona. In the case of a poly(butadiene-b-styrene) star a weak increase of the re lative viscosity is observed at concentrations between two and three t imes the overlap concentration.