Phase diagrams were determined for poly(vinylidene fluoride) (PVDF) and a terpolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene (VDF/HFP/TFE) in solutions composed of 1-octanol and dimethylformamide at 25°C. From the measured gelation and liquid–liquid phase separation data, binary interaction parameters were computed using a modified Flory–Huggins theory. PVDF microporous membranes were then prepared by isothermal immersion precipitation processes in various doping conditions. The formed membrane exhibited a particulate morphology characterized by a uniform package of spherical particles of identical size. These particles were identified to be full spherulites of PVDF using scanning electron microscopy, differential scanning calorimetry and small angle light scattering techniques.