Radiation damage of polymers studied by positron annihilation

本研究项目旨在应用正电子湮灭研究聚合物的特性，特别是辐射损伤聚合物。本研究第一年，采用高密度聚乙烯（HDPE）、线性低密度聚乙烯（LLDPE）、支链低密度聚乙烯（BLDPE）、超高分子量聚乙烯（UHMWPE）和全拉伸聚乙烯（TEKMIRON） 5种聚乙烯（PE）进行辐射损伤实验。TEKMIRON的机械强度是其他材料的100倍，但经过3MGy的辐照后，其强度降低了未辐照材料的1/10，而其他材料的强度仅降低了1/2。通过正电子湮灭（PA）实验，得到了邻位ps的强度（I3）和寿命（tau3）。TEKMIRON的I3和tau 3比其他的小。这可以用结晶度来解释。得到了PA参数与辐照PE强度之间的相关性。第二年，正电子的特性被广泛应用于研究从液体到固体的状态转变、PE的热氧化效应、新型环氧树脂的三维网络结构。特别是，PA是研究状态转变的有效手段，是研究环氧树脂聚合反应的第一个方法。此外，PA已被广泛应用于集成电路工业中使用的新型环氧树脂中，研究表明，聚合物的防潮性与孔的大小密切相关。

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.