D. Schwahn and L. Willner

Binary blends of statistical polybutadiene copolymers of different vinyl content were explored by small angle neutron scattering. These samples represent the most simple class of statistical copolymer mixtures. Even though the components differ only slightly strong changes of phase behavior were observed with vinyl content; phase separation occurs between minus 230°C to more than plus 200°C and the phase separation can even reverse from an enthalpic driven one at low temperatures (UCST) to an entropically driven one at high temperatures (LCST). While for most samples the experimentally determined entropic term of the Flory-Huggins parameter is in excellent agreement with Lattice Cluster Theory Calculations the theoretical enthalpic term does not at all describe our experimental data.