用C-13核磁共振谱测定高聚物中微量异种结构单元的探讨

Detection of Various Branched Structure Units in High Polymers by Carbon-13 NMR

通过高低工作频率的高分辩率核磁共振谱仪(型号分别为GX_400和FX_90Q)对含有不同微量异种结构单元的聚乙烯样品作了 13C谱测量和比较分析;结果表明 13C谱在较高磁场频率 (100.4MHz)条件下可检测灵敏度达到0.5个支化点/10000个碳原子(0.5/10000C) ;而较低磁场频率 (22.5MHz)只达到1个支化点/1000个碳原子(1/1000C)以上;综合分析所得结果 ,指出在用电磁体系列 (谱仪频率一般为90MHz或100MHz)核磁共振谱仪检测高分子量物质时 ,应注意有遗漏1/1000C以下浓度结构的可能性 ;分析了 13C谱可检测灵敏度与磁场强度等因素的关系 ,得到了可检测灵敏度S/N与磁场强度 (H0)间比较适合的关系式。

High _ resolution NMR at various frequencies can be employed for the detection of micro amounts of various branched structure units in polyethylene. Under a higher frequency(100.4 MHz), the observed sensitivity of 13C NMR is about 0.5 branch per 10 000 carbon atoms. Under a lower frequency(22.5 MHz), however, only those structure units with more than 1 branch per 1 000 carbon atoms can be detected. Attention should be paid to the possibility of detection failure for branched structure units below 1 branch per 1 000 carbon atoms. An appropriate relationship between the sensitivity S/N of the method and the magnetic field strength H0 has been established: S/N=.