Abstract: A process is provided for preparing a graft polymermodified cellulose pulp filler from cellulose sulfite pulp having an R.sub.18 value greater than 80%, which comprises adding to the pulp a redox initiator; washing the pulp with water having a pH below 5 in an amount sufficient to adjust the redox initiator cation content to within the range from about 5 to about 1000 ppm of cellulose sulfite pulp; adding hydrogen peroxide in an amount to provide within the range from about 0.1% to about 4% H.sub.2 O.sub.2 by weight of the sulfite pulp; and then reacting the pulp with at least one monomer having the formula: ##STR1## in which: R.sub.1 is hydrogen or methyl; andR.sub.2 is selected from the group consisting of nitrilo --CN, ##STR2## and COOR.sub.3 groups, wherein R.sub.3 is selected from the group consisting of methyl, ethyl, n-butyl, isobutyl and 2-ethylhexyl; at a temperature at which grafting of the monomer onto the cellulose polymer molecule proceeds but below about 70.degree. C.