The radiation-induced racemization and chain-scission of crystalline isotactic poly (methyl methacrylate) (i-PMMA) were studied with proton NMR

DSC and molecular weight(MW) determination. It is shown from MW results that the chain-scission reduces in crystalline phase. Its G-value is only half of that in amorphous region. NMR study on the radiation-induced change of stereospecific structure indicates that iso-PMMA transforms gradually into syndiotactic and atactic ones

similar to what happens in amorphous phase.However

radiation-induced racemi-zation in crystalline state is more remarkable than chain-scission reaction.Such an effect could be well explained with the effect of "cage"and steric hindrance on above-mentioned two reac-tion mechanisms

as we proposed before.Because of both reactions taking place within cystal-line region

the reduction of melting point of iso-PMMA with radiation dose is more remarkable.The G-value of the damage in crystalline phase estimated is 8.8

which is much higher than that in polyethylene.