isotropic porous polymer beads having a high surface porosity and large pore diameters from about 0 . 002 to about 5 microns are produced from solutions of an acrylonitrile polymer or a copolymer by a thermally - induced phase separation process . the use of mixed solvent - non - solvent combinations as solvents for the polymers , produces high pore content , substantially spherical beads having a morphology ideally suited to the chromatography of large molecules , such as proteins , and for enzyme - binding .