The invention provides a method for preparing a polymer useful for treating and modifying the hair. The method for preparing a polymer composition comprising the step of (a) preparing a copolymer comprising, as polymerized monomer units, (i) 50 to 89.9 wt.% of one or more ethylenically unsaturated monomer and (ii) 10 to 40 wt.% of 2-acrylamide-2-methyl-1-propanesulfonic acid and salts thereof, byvarying addition of monomers (i) and (ii) with respect to time and each monomer prior to neutralizing the polymer with a base.