The branched multiblock copolymer based on fatty acid, methyl methacrylate and PHB was first time synthesized. Autoxidation is the reaction of unsaturated fatty acids with air oxygen leading to macroperoxide initiators. Poly (3-hydroxy butyrate), PHB, is a natural bio polyester accumulated in the bacterium cell of some bacteria. Tri hydroxyl derivatives of PHB were obtained by the modification reactions of PHB with di-ethanol amine. Hydroxyl ends of the modified PHB were capped with the autoxidized unsaturated fatty acid oligomeric peroxides in order to the polyoleic acid, polylinoleic acid and polyricinolenic acid. PHB based macroperoxides were used free radical polymerization of methyl methacrylate in order to obtain branched multiblock copolymers. It is desirable to combine the biodegradability of the PHB and fatty acid with the excellent application properties of polyvinyls. PHB based macroperoxides were also obtained in two steps. First, pristine fatty acid was attached to PHB-OH to obtain PHB-fatty acid conjugate. Second, PHB-fatty acid conjugate was mixed with free fatty acid and autoxidized together with for two months. The products were characterized by 1H NMR, DOSY, SEC, FTIR, SEM, DSC and TGA techniques.