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

本文通过核磁氢谱、DSC和分子量测定,研究了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.分子量测定的结果表明,等规立构聚甲基丙烯酸甲酯结晶后,其辐射裂解反应减弱,裂解G值减小将近一半.核磁氢谱测定辐照试样的空间立构变化结果为:随着辐照剂量的增加,等规立构逐渐变为无规立构和间规立构,其变化规律相似于非晶试样.结果还表明,晶区的消旋反应比裂解反应更为显著.DSC测得的试样熔点,随着辐照剂量的增加而急剧下降,由Flory结晶熔化理论计算得晶区的辐射破坏G值为8.8.该值远大于聚乙烯晶区的破坏G值.

THE RADIATION-INDUCED RACEMIZATIOIN AND CHAINSCISSION IN CRYSTALLINE ISOTACTIC POLY (METHYL METHACRYLATE)

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 racemization 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 reaction mechanisms, as we proposed before. Because of both reactions taking place within crystalline 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.