The title aq. polymer contg. pyrrolidinium chloride units is stirred with heating until a water content of <25% is reached, to provide a powder. The polymer is a binary copolymer of diallyldimethylammonium chloride (I) with methyltriallylammonium chloride (II), tetraallylammonium chloride, or methylenebisacrylamide. Thus, 400 mol 50% aq. I soln. was stirred at HO Deg with 2 mol % each ammonium peroxydisulfate and ammonium carbonate. After addn. of 1 mol % triethanolamine and 0.5 mol II, polymn. was continued. The copolymer was heated and stirred with water removal to give a powder with active substance content 70%. [on SciFinder (R)]