In order to produce transparent HIPS

the methyl methacrylate(MMA) was used to copolymerlze with styrene (St) by using chemically initiated prepolymerization followed by radiation-induced polymerization at room temperature．The influence of the absorbed dose and dose rate on the molecular weight of P(St-co-MMA) copolymers was investigated．The chemical structure of resulting P(St-co-MMA) copolymers was confirmed by using FTIR

1H-NMR and DSC．In addition．the transparency of copolymers was measured by means of a UV-Vis spectrometer．and their mechanical strength was compared with that of the pure PS．Experimental results show that it is helpful to obtain the high molecular weight copolymers by increasing the conversion of prepolymefization and decreasing the dose rate．With increasing the absorbed dose

the accelerated polymerization occurred

and molecular weight of copelymers reached a maximum

then decreased slighdy with the dose．The synthesized P(St-co-MMA) copolymers were identified to be ataetic polymers and they have nsrrow polydispersity of molecular weight．Comparing with pure PS

the copolymer has higher mechanical strength and better transparency

particularly the toughness was improved significantly．Therefore

transparent P(St-co-MMA) copolymers with high mechanical performance could be produced by combining chemical initiation polymerization and radiation-induced polymerization．The process is easy to control and will be expected to be used for preparing transparent HIPS.