Systems for processing dope for the manufacture of microporous phase inversion membrane having any one of a plurality of different pore sizes from a single master dope batch is disclosed. The systems and methods include formulating a single master batch of dope preferably maximizing the non-solvent to solvent ratio for a given weight percentage of polymer for use in a microporous phase inversion membrane casting operation to produce phase inversion membranes having one of a plurality of different predetermined pore sizes. The master dope batch is controllably formulated in a vessel such that the temperature of the dope does not exceed a predetermined maximum mixing temperature and is maintained at a relatively low temperature (lower than the mixing temperature) suitable for storage. A small portion of the dope is then sequentially heated to a temperature no higher than any one of a plurality of target temperatures, the target temperature corresponding to a specific desired pore size to be formed in the microporous phase inversion membrane that results from casting the dope. As portions of the dope are incrementally transferred from the vessel to the dope casting apparatus, the dope portions are heated to a temperature no higher than within about .+-.0.15.degree. C. of the target temperature. The dope is then cooled to about room temperature or the temperature which results in a suitable and/or optimal casting viscosity and transferred to the dope casting apparatus to be forming microporous phase inversion membrane having any one of a plurality of different possible pore sizes.