Phase behavior of binary polybutadiene copolymer mixtures as an example of weakly interacting polymers

Binary blends of statistical polybutadiene copolymers of different vinyl content and molar volume were explored by small-angle neutron scattering. These samples represent the most simple class of statistical copolymer mixtures. In spite of this simplicity, changes in vinyl content, molar volume, and deuterium and hydrogen content of the chains give rise to strong effects; phase separation occurs from minus 230 °C to more than plus 200 °C and can even reverse from an enthalpically driven one at low temperatures to an entropically driven one at high temperatures. The entropic and enthalpic terms of the Flory–Huggins parameter as determined from the experiment are in excellent agreement with lattice cluster theory calculations.