modified pacs according to the invention can be used as they are in some cases these modified pacs improve the physicochemical properties of a product promote the increase in their viscosity and the reduction in their content of initial pac in the remainder of the present description examples are given to illustrate the invention without however wishing to limit the scope thereof the present example describes a free radical polymerization process according to the invention applied to an aromatic extract of a distillate under vacuum hereinafter u201c extract u201d consisting of a 350 u00b0 c to 550 u00b0 c petroleum cut containing 100 ppm of pac to modify these pacs the procedure is carried out on the laboratory scale in a 100 ml two necked round bottomed flask provided with a condenser and an inlet for an inert gas nitrogen equipped with a stirrer and placed in an oil bath thermostated at 80 u00b0 c for 6 hours several mixtures were tested and are referenced in table i as samples x 1 to x 7 after reaction the excess monomer was evaporated under vacuum each sample thus prepared was analyzed by gc ms coupling gas chromatography mass spectrometry in order to measure the content of pahs content in the pacs of the samples x 1 to x 7 after free radical polymerization the results of these analyses in relation to the nature of the pahs still present are given in table ii below the toxicity of the samples is in agreement with the dossier no 92 101 entitled u201c aromatic extracts u201d page 7 by concawe the oil companies european organization for environmental and health protection it is observed that the most toxic pah compounds are removed at more than 50 within.