一种改进的溶剂萃取法测定聚丙烯等规度

An Improved Solvent Extraction Method for Measurement of Polypropylene Isotacticity Index

采用一种先将聚丙烯溶解于沸腾正辛烷,然后用正庚烷抽提室温下不溶于正辛烷部分的两步分级方法(简称两步法),可将聚丙烯试样中的无规、低等规聚丙烯与高等规聚丙烯进行分离。对所得级分进行了13C NMR,GPC,DSC表征,结果发现,室温下正辛烷可溶级分由无规聚丙烯和少量低等规聚丙烯构成,沸腾正庚烷可溶级分由中等规聚丙烯构成,沸腾正庚烷不溶级分则为高等规聚丙烯。通过对比发现,采用传统的正庚烷抽提聚丙烯试样来测定等规度不能将试样中的无规聚丙烯和中低等规聚丙烯完全分离出来,等规度的测定值低于真实值。两步法克服了传统方法的缺陷,可对聚丙烯试样的等规度进行快速且可靠的评价。

A two-step procedure was adopted to fractionate polypropylene （PP） sample into high isotactic PP, low isotactic PP and atactic PP. In the first step, PP sample was dissolved in boiling n- octane and then the solution was cooled to room temperature. In the second step, the fraction insoluble in n-octane at room temperature was extracted by boiling n-heptane. The fractions were characterized by means of ^13C NMR, GPC and DSC. The fraction soluble in n-octane at room temperature was a mixture of atactic PP and a little low isotactic PP with low relative molecular mass. The fraction soluble in boiling n-heptane is moderate isotactic PP and the fraction insoluble in boiling n-heptane is high isotactic PP. In comparison, the traditional method for measurement of isotacticity index which is based on direct extraction of PP with boiling n-heptane can＇ t dissolve all the PP chains with atacticity and low isotacticity into the solution, so lower isotacticity index is given. The two-step fractionation method can give a precise and quick measurement of PP isotacticity.