几种硅橡胶次级链结构辐射稳定性的理论研究

Theoretical exploration for radiation stability of several silicone secondary chains

采用密度泛函理论的B3LYP方法,以硅橡胶泡沫材料单体二甲基硅氧烷和甲基乙烯基硅氧烷为基础,研究了这两种单体和由其构成的四种次级链结构的相关能量、前沿轨道、振动分析等相关信息。结果显示,前沿轨道显示链结构的敏感点应在含Si-Si键的链端和乙烯基部分,分子链结构中的原子排布更易形成共轭或等效于共轭的离域结构时,在遭受辐照等能量注入的情况下可以将能量及时转移而一定程度上避免了链结构的断裂;在遭受外界能量注入时,裂解的部位发生在共轭链段间隙处和前沿轨道所显示的敏感点的可能性比较大。此外,也可以看到甲基乙烯基硅氧烷的引入在一定程度上可以增加材料的化学稳定性却并非一定会对材料的耐辐照稳定性起到增强作用,这应与单体的比例以及乙烯基片段在齿形波动的长链结构中所处的位置有着密切关系。

The density functional theory （DFT） based hybrid-method B3LYP is used to study the chemical conformation, frontier molecule orbital （FMO）, spectral analysis, and electrostatic potential （ESP） of dimethyl siloxane （mono-A）, methyl vinyl siloxane （mono-B）, and four kinds of short chains and secondary chains, short as A2B1, A3B1, A3, A4, and A8B1, ATB2, A6B3, A5B4. It shows that the susceptible locations of the chains ought to be the Si-Si amphi-chains and the vinyl group. The more possible stabilization, the more conjugated or semi-conjugated structure in the chains, and it maybe because energy can avert easily in the circumstances. When the chain splits, the splitting point ought to be at the gap of conjugated or semi-conjugated structures and the susceptible positions shown from FMO. Besides, the chemical stability of silicone foam material is raised at the extent of the concentration of mono-B, but there would not be linear relationship between it and the radiation stability, which should be dose relevant to the quantity or proportion of mono-B and the positions where vinyl groups locate on the long chain.