impact strength was measured at 23 u00b0 c according to jis k 7110 the light transmission and haze value were measured according to jis k 6714 the results are shown in table 1 wherein 34 mma 34 34 st 34 and 34 ba 34 represent methyl methacrylate styrene and butyl acrylate respectively a polymerization vessel was charged with 210 parts of the rubber latex a1 obtained in example 1 solid matter 70 parts 60 parts of water 0 002 part of ferrous sulfate 0 004 part of disodium ethylenediaminetetraacetate 0 1 part of formaldehyde sodium sulfoxylate and 1 5 parts of potassium chloride to the vessel were continuously added 13 parts of methyl methacrylate 2 parts of butyl acrylate and 0 1 part of cumene hydroperoxide over 3 hours at 70 u00b0 c after further continuing the polymerization for 1 hour 15 parts of styrene and 0 1 part of cumene hydroperoxide were then continuously added to the vessel over 3 hours the polymerization was further continued for 1 hour to give an aqueous latex of a graft copolymer a mbs resin was recovered from the latex and the test was made in the same manner as in example 1 a polymerization vessel was charged with 210 parts of the rubber latex a1 obtained n example 1 solid matter 70 parts 60 parts of water 0 002 part of ferous sulfate 0 004 part of disodium ethylenediaminetetraacetate 0 1 part of formaldehyde sodium sulfoxylate and 1 5 parts of potassium chloride to the vessel were continuously added 13 parts of methyl methacrylate and 0 1 part of cumene hydroperoxide at 70 u00b0 c over 3 hours after further continuing the polymerization.