THE RADIATION-INDUCED RACEMIZATIOIN AND CHAINSCISSION IN CRYSTALLINE ISOTACTIC POLY (METHYL METHACRYLATE)
结晶对等规立构聚甲基丙烯酸甲酯辐射消旋和辐射裂解的影响

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.