Graft polymer dispersion having a third monomer and polyurethane foams having a reduced tendency to shrink prepared thereby

A stable low viscosity graft polymer dispersion comprising from 25 to 60 weight percent based on the total weight of the polymer dispersion of a mixture of at least three ethylenically unsaturated monomers polymerized in the presence of a reaction moderator and a free radical initiator in a polyol mixture initially containing less than 0.1 moles of induced unsaturation per mole of said polyol mixture;

• wherein said mixture of ethylenically unsaturated monomers comprises (a) acrylonitrile, (b) 40 weight percent to 80 weight percent, based on the weight of the monomer mixture, styrene or 4-methylstyrene, and (c) 10 weight percent to 25weight percent, based on the weight of the monomer mixture, 2-hydroxyethyl methacrylate.