Graft copolymer (P) which exhibit pH dependent swelling/dissolution properties comprising a hydrophobic back-bone and graft chains comprising acidic monomer. This Graft copolymer (P) do not swell or dissolve at acidic pH prevalent in the stomach and they swell/dissolve at near neutral pH prevalent in the intestinal region. The graft copolymer (P) is useful for the development of drug delivery formulations particularly for oral drug delivery formulations.