摘要：The graft copolymer of sulfonated St and MA has a certain steric hindrance due to its sulfo group and polyethylene glycol (PEG) macromolecular group, and can ionize a certain charge to maintain a certain electrostatic force. Thereby making it more effective. Due to its special molecular structure, St-MA copolymers and their derivatives have high surface activity and low interfacial tension, so they have broad application prospects in emulsification, thickening and flocculation.The presence of maleic anhydride moiety in styrene-maleic anhydride (SMA) copolymer makes it a versatile substrate for conjugation of drugs. In this study biocompatible styrene-maleic anhydride (SMA) copolymer with alternating structure was synthesized by gamma irradiation at room temperature in the presence of 2-phenyl-2-propyl benzo- dithioate (PPB). Then sulfonated to obtain styrene-malefic anhydride(SSMA) by used as water-based drilling fluid viscosity reducing agent. The effects of monomer ratio， polymerization temperature，initiator content and reaction time on the viscosity reduction of the product were studied. The results showed that the optimum synthesis conditions of SMA were as follows:molar ratio of St and MA was 2:1, the polymerization temperature was 70°C, the content of initiator was 2% (total weight of monomer) and reaction time h.
