Method of manufacturing rubber modified styrene resins

In a method of continuously manufacturing rubber modified styrene resins from a styrene monomer and a butadiene polymer by bulk polymerization or solution polymerization using an organic peroxide as an initiator of radical polymerization, the improvement comprising:

• (A) a first step of using a single or a plural number of agitator type polymerization vessels connected in series, continuously supplying 100 parts by weight of the styrene monomer and 3 to 15 parts by weight of the butadiene polymer per unit time to the first polymerization vessel, feeding continuously 0 to 0.003 parts by weight of the organic peroxide per said unit of time to the first vessel in full amount or to a plurality of polymerization vessels in divided portions, and conducting polymerization until the polymerization yield of the styrene monomer in the final polymerization vessel becomes 2 to 5 times more than the weight of the butadiene polymer;
• and
• (B) a second step of continuously feeding to the first stage of a single or plural number of reactors connected in series the full amount of polymerization liquid discharged from the first step, 0 to 200 parts by weight of fresh styrene monomer per said unit of time, and 0.01 to 0.2 parts by weight of fresh organic peroxide per said unit of time, and conducting polymerization until the polymerization yield of the styrene monomer in the final stage is at least 1.5 times the yield in the first step.