Radiation damage of polymers studied by positron annihilation

本研究旨在应用正电子湮没技术研究聚合物，特别是辐射损伤聚合物的特性。本研究第一年采用5种聚乙烯(PE)：高密度聚乙烯(HDPE)、线性低密度聚乙烯(LLDPE)、支化低密度聚乙烯(BLDPE)、超高相对分子质量聚乙烯(UHMWPE)和全拉伸聚乙烯(TEKMIRON)进行了辐射损伤实验。TEKMIRON的机械强度是其他材料的100倍，但在3MGY辐照后，其强度降低了未辐照材料的1/10，而另一种材料的强度仅降低了1/2。通过正电子湮没实验，得到了正电子湮没强度(I_3)和寿命(T_(U3))。TEKMIRON的I3和tau3较小，这可以用结晶度来解释。第二年，正电子特性被广泛应用于研究液体到固体的状态转变、PE的热氧化效应以及酚醛树脂的三维网络结构。特别是，PA是研究状态转变的有效方法，这是首次研究环氧树脂聚合的方法。此外，PA已被广泛应用于集成电路工业中使用的酚醛环氧树脂，研究表明，耐湿性与聚合物中的孔洞大小密切相关。

This research program aims at the application of positron annihilation for studying characteristics of polymers : especially radiation damaged polymers.First year of this research, 5 kinds of polyethylenes (PE) : high density PE (HDPE), linear low density PE (LLDPE), branched low density PE (BLDPE), ultra-high molecular weight PE (UHMWPE), and fully stretched PE (TEKMIRON), were employed for radiation damage experiments. TEKMIRON has 100 times larger mechanical strength than the others, but after irradiation of 3MGy its strength is reduced 1/10 of unirradiated materials, while the other's strength is reduced only 1/2. From experiments of positron annihilation (PA), intensities (I3) and lifetimes (tau3) of ortho-Ps are obtained. I3 and tau 3 of TEKMIRON are smaller than that of others.This can be explained by the crystallinity. Correlation was obtained between PA parameters and strength of irradiated PE.Second year, characteristics of positrons are extensively applied to study state transition from liquid to solid, thermal oxidation effect of PE, and three dimensional network structure of novolach epoxy resins. Especially, PA is effective to study the state transition and this work is the first approach to investigate polymerization of epoxy resins. Furthermore, PA has been applied to widely utilized novolach epoxy resins for integrated circuit industries and it has been shown that moisture resistence is strongly correlated with the size of holes in polymers.