The present invention relates to a novel polymerisate, which is prepared by applying the method of atom transfer radical polymerisation. The novel polymerisate is useful for stabilising a composition of matter susceptible to degradation induced by light, heat or oxidation. The novel polymerisate is also useful as a dispersant in a pigment dispersion containing dispersible inorganic or organic pigment particles. Further embodiments of the invention relate to the process for preparing the novel polymerisate by applying the method of controlled or “living” polymerisation and to the use of the pigment dispersion for preparing inks, colour filters, coatings, images, lacquers and others.