PURPOSE: To produce the polymer which does not flocculate even in the copresence of an anionic surfactant and thickener and to improve the white ground of the diffusion transfer type color photosensitive material and heat developable photosensitive material to obtain a image having a excellent discrimination as well as to improve the color image fastness of the dye fixing element.

CONSTITUTION: An aq. soln. contg. the anion of formula (III) is added to an aq. soln. contg. the polymer of formula (I) and the compd. of formula (II). The soln. is then desalted to exchange the counter anion of the polymer of the formula (I) with the anion of the formula (III). The formula (I): -(A)x-(B)y-, the formula (II): R1-(O-CH2-CH2)n-OR2, the formula (III): R3-(J)n-D-, A denotes a vinyl monomer unit having a quanternary ammonium slat; B denotes a vinyl monomer unit having no quaternary ammonium salt; (x), (y) denote mol%; R1, R2 denote hydrogen or substituent; (n) denotes integer ≥1; R3 denotes a substituent; J denotes a combination group; D- denotes an anionic dissociation group; (m) denotes 0 or 1.