the like, methacrylic polymers or copolymers such as polymethacrylic resins and the like and tetrafluoroethylenic polymers or copolymers such as polytetrafluoroethylene and the like, or into a modified polymer or copolymer base to be prepared by modifying the polymers or copolymers with a crosslinking agent such as divinylbenzene or the like; and also mentioned are inorganic cation-exchanging mate