A number of highly cross-linked porous polymers have been synthesized by the polycondensation of hexachlorocyclotriphosphazene and piperazine. It was found that the nature of solvents, used for the synthesis and purification of the resulting porous polymer, may significantly affect the porosity of the polymer. Thus, the use of polar tetrahydrofuran leads to an increase in the porosity owing to a higher conversion of reactive groups and higher cross-linking degree. The use of methanol for the purification of polymers by the extraction method leads to a decrease in the porosity due to the replacement of piperazine units.