Phase diagrams for polystyrene solutions in poor solvents and theta-solvents have been determined as functions of concentration, molecular weight and polydispersity, pressure, temperature, and H/D isotope substitution on both solvent and polymer, sometimes overbroad ranges of these variables. The phase diagrams show upper and lower consolute branches and contain critical and hypercritical points. The isotope effects are large, sometimes amounting to tens ofdegrees on critical demixing temperatures. Most often solvent deuterium substitution decreases the region ofmiscibility and substitution on the polymer increases it. The demixing process has been investigated using dynamic light scattering (DLS) and small angle neutron scattering (SANS), examining pressure and temperature quenches from homogeneous conditions to near-critical demixing. The SANS and DLS results (which refer to widely different length scales) are discussed in the context of scaling descriptions of precipitation from polymer solutions.

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