The invention concerns a novel photosensitive composition for photoresist and a system comprising a substrate and a photoresist obtained from said novel composition. The photosensitive composition for photoresist comprises a copolymer with hydrophobic blocks whereof at least one block is an hydrophobic block capable of generating a hydrophilic block and comprising at its end a group selected among dithioesters, thioesters-thiones, dithiocarbamates and xanthates, and a photoactive compound capable of generating under the effect of a radiation an active species reacting with the hydrophobic block to generate the hydrophilic block.