采用等温和非等温差示扫描量热(DSC)法研究了聚丙烯规整性和分子量对其结晶性能的影响.结果表明,采用等温结晶分析.聚丙烯的规整性与其熔点成线性关系.但对于分子量很低或规整性很高的聚丙烯,其熔点和规整性不符合以上线性关系.采用非等温结晶分析,聚丙烯规整性的对数与其熔融焓的对敷成线性关系.对乙烯共聚研究结果说明,对高规整性聚丙烯,极少量乙烯共聚也会影响其规整性.
The crystallization behavior of polypropylenes (PP) prepared with Ziegler-Natta catalytic systems was studied by isothermal and nonisothermal differential scanning calorimetry (DSC). The effects of isotacticity and molecular weight on the crystallization behavior were investigated. Isothermal crystallization studies show that the melting temperatures of the PPs increase linearly as a function of the average meso run length (MRL) or the content of [mmmm]. However, the PPs with low molecular weight show low melting point, although they have high MRL value. The results obtained from non-isothermal crystallization show that the enthalpy of crystallization is related to the isotacticity by an equation of the form: lg△H = mlg(isotacticity) + c. This relationship is found to be applicable to samples from high molecular weight to low molecular weight. The crystallization studies clearly indicate the low ethylene content has important effect on the isothermal crystallization behavior.
参考文献
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