at 20 u00b0 c with 1 52 g of ammonium persulfate for 10 minutes under a nitrogen purge pad 680 g of a 50 water solution of 2 acrylamido 2 methylpropanesulfonic acid sodium salt were added over 10 minutes to the blend of carboxymethyl cellulose and initiator while keeping the temperature at 19 u00b0 20 u00b0 c using continuous stirring the reaction mixture was heated to 65 u00b0 70 u00b0 c and held at this temperature under stirring for 30 minutes the reaction mixture was then heated to 70 u00b0 75 u00b0 c and held for 60 minutes at this temperature the mixture was cooled to 45 u00b0 c and dried to remove excess moisture and subjected to grinding to give the filtrate reducer rf2 the brookfield lvt viscosity at 60 rpm and 20 u00b0 c of rf2 is 71 mpa u00b7 s in 2 deionized water solution a filtrate reducer is prepared by mechanically mixing 94 parts by weight of rf2 and 6 parts by weight of sodium thiosulfate to obtain the filtrate reducer rf2t a homopolymer of 2 acrylamido 2 methylpropanesulfonic acid sodium salt was synthesized by reacting a 42 water solution of amps sodium salt in the presence of sodium metabisulfite at 75 u00b0 c the resulting homopolymer was isolated dried and mixed.