γ辐照聚全氟乙丙烯(F_(46))的电子自旋共振研究 Ⅰ.真空中俘获自由基的定量研究

建立了从ESR叠加谱分别测定γ辐照F_(46)产生的…CF_2-C(CF_3)-CF_2…,…CF_2-CF_2.及…CF_2-CF-CF_2…三种真空中俘获自由基含量的方法.研究了自由基浓度与辐照剂量的定量关系;计算了三种自由基的辐射化学产额(G值)分别为2.0,1.2和O.59;讨论了自由基G值与全氟型高聚物结构的关系、自由基浓度随剂量的饱和现象以及自由基在晶区和非晶区分布等问题.     

γ辐照 聚全氟乙丙烯(F46)的电子自旋共振研究 I.真空中俘获自由基的定量研究

A method for determining respectively the concentration of free radicials...CF2-CF2.(RI), ...CF2-CF-CF2...(RII)and...CF2- C(CF3)-CF2...(RIII) trapped in γ-irradiated F46 in vacuum at room temperature by analysing the ESR overlapping spectra is proposed. A quantitative relation between the concentration of free readicals and the total dose of γ-irradiation has been studied. The generating rate o free radicals caused by irradiation, i.e. G-value, has been calculated; it is 2.0 for RIII, 1.2 for RI, and 0.59 for RII. the magnitude of G value of free radicals is in the reverse order of their stability. Hence, we assume that the G value of free radicals in F46 mainly depends on the escaping rate of F2 and other fluorine-containing small molecules from surface of polymer into space. Therefore the looser the molecular chain, the larger becomes the G value of free radical. From that, we consider that both unstable free radicals RIII and RI with larger G-value mainly locate in the amorphous region, and the stable free radical RII with lower G-value is in the crystalline region. Recombinations between free radicals RII and RIII, or between RII and RI are forbidden at the temperature lower than 80C. An explanation for the saturation phenomenon of concentration of free radicals is given.     

γ-辐照聚全氟乙丙烯的电子自旋共振研究 II: 真空中俘获自由基的自氧化过程

Autooxidation processes of free radicals trapped in γ irradiated F46 copolymer in vacuum at room temperature were studied by means of ESR. It is shown that these processes are under the dual control of both the diffusion of oxygen and the total concentration of free radicals, and they are independent of the autooxidation reaction rate constant. In general, the diffusion constant calculated by simple diffusion equation is an apparent diffusion constant, it is a function of the total concentration of free radicals. Only when the total concentration of free radicals is low enough (in our case n相似文献   

γ-辐照聚全氟乙丙烯的电子自旋共振研究 Ⅱ.真空中俘获自由基的自氧化过程

电子自旋共振(ESR)研究表明: (1)在真空中γ-辐照F_(46)产生的俘获自由基暴露于空气后逐渐转化成过氧化自由基,其常温ESR谱为单峰,g=2.0148±0.0009,ΔH_(PP)=18.9±1.5G. (2)F_(46)真空中俘获自由基的自氧化反应是一个既受氧的扩散速度控制,又与自由基浓度有关的双因素控制的过程,而与自氧化反应的速度常数无关. (3)氧在γ-辐照F_(46)中的扩散系数与自由基浓度有关,而与自由基种类无关.在自氧化过程中位于晶区的仲碳自由基…CF_2-CF-CF_2…从晶区内部快速“转移”到晶区表面与氧反应. (4)以ESR方法用单纯扩散动力学公式测定的氧在全氟型高聚物中的扩散系数,一般是以自由基浓度为函数的表观扩散系数,仅当自由基浓度足够低时(对于本文所采用的悬浮法F_(46)薄膜样品而言,n≤2×10~(17)spins/g)才能求得接近未辐照样品时的真实扩散系数. (5)用本法求得氧在悬浮法F_(46)薄膜中的扩散系数D=1.6×10~(-7)cm~2/sec(20℃).     

带固定内标的电子顺磁共振定量测量方法

自旋浓度是最重要又是最难精确测量的EPR波谱数据之一,常用比较法测量。经典的比较技术要求未知样品和标准样品在完全相同的实验条件下记谱,这实际上很难做到,特别是当更换样品时,常因样品介电损耗的差别带来仪器灵敏度很大变化。一些作者采用固定内标作为仪器灵敏度变化的指示,以消除仪器因素带来的误差,但仅适用于固定内标与未知或标准样品信号不重叠的场合。本文详细地讨论这种定量方法,并进行若干改进,提出了一套固定内标系列和工作标准系列,并配以相应的实验程序,可以满足各种样品测量的需要。实验表明:这种定量方法有较好的再现性和准确度。文中还引进等效自旋数的概念,并建议用为比较不同类型样品信号强度的统一单位,同时列出由等效自旋浓度计算顺磁离子重量百分数的公式。最后提出相对饱和特性参数Sx的定义并用