聚甲基丙烯酸甲酯辐射裂解和消旋的空间立构效应

本文研究了三种不同空间立构聚甲基丙烯酸甲酯的辐射效应,提出裂解过程是一种裂解与重合的动态平衡过程。分子量降低和消旋作用对温度的依赖性,是由于分子运动和笼罩效应以及重合的空间位阻效应所致。辐照温度愈高,裂解产额愈大。相同条件下辐照,全同立构比无规立构试样的裂解产额更大。 全同立构聚甲基丙烯酸甲酯辐照后,不仅分子链断裂,而且空间立构也发生很大变化。随着辐照剂量的增加,全同立构含量逐渐减少,而无规立构含量和间同立构含量却逐渐增加。

THE STERIC EFFECT ON THE RADIATION-INDUCED CHAIN SCISSION AND RACEMIZATION OF ISOTACTIC POLY (METHYL METHACRYLATE)

The radiation effect on poly (methyl methacrylate) with different tacticities was studied. It was proposed that chain scission process was in a kinetic equilibrium between scission and recombination. The dependence of chain scission and racemization on temperature results from molecular motion, "cage effect" and steric hindrance during recombination. G-value of chain scission increases with irradiation temperature. For isotactic PMMA, it is greater than that for atactic one.For isotactic PMMA, radiation induces not only chain scission but also racemization. Isotactic diad decreases with the increase of radiation dose. Meanwhile, atactic and syndiotactic diad increases.