The present invention concerns a block copolymer composed of two blocks S1 and S2, wherein S1 consists of m(PEG)n, where n is an integer in the range between 4 and 50 and S2 is a random copolymer consisting of the monomer units R1 and R2 where R1 is the monomer unit corresponding to the monomer &gamma；-valerolactone and R2 is the monomer unit corresponding to the monomer selected from the group consisting of &egr；-caprolactone, &delta；-valerolactone, &bgr；-butyrolactone, &egr；-caprolactam, &delta；-valerolactam. A method for the preparation thereof, the use thereof, nanoparticles and a pharmaceutical composition comprising the same is also provided.
