窄分子量分布茂金属短链支化聚乙烯结晶动力学

CRYSTALLIZATION KINETICS OF NARROW MOLECULAR WEIGHT DISTRIBUTION METALLOCENE SHORT-CHAIN-BRANCHED POLYETHYLENE

本工作用DSC方法对三种不同支化度的茂金属短链支化聚乙烯的等温、非等温结晶行为进行了研究 .样品为乙烯和己烯 1的共聚物 ,短支链主要为正丁基 ,分子量Mw =2 0 ,0 0 0 ,Mw/Mn<1 15 ,支化度 (每10 0 0C中CH3 数目 )分别为 1 6、10 4、40 .实验结果表明 ,茂金属短链支化聚乙烯结晶方式Ⅰ Ⅱ转变温度随支化度增加而降低 ,分别为 119 8℃、115 9℃、113 3℃ ;同时支链的存在降低了二次成核速率 ,增大了方式Ⅰ的结晶范围 。

Isothermal and non\|isothermal crystallization kinetics of three metallocene\|catalysed short\|chain\|branched polyethylene (SCBPE) fractions with different degree of branching were investigated by using differential scanning calorimetry (DSC).Narrow molecular weight fractions ( M w=20,000 and M w/ M n<1.15) are used and the degree of branching (CH\-3 per 1000C) are 1.6, 10.4, 40 respectively.The regime Ⅰ\|Ⅱ transition temperature are 119.8℃, 115.9℃, 113.3℃ with the decreasing of degree of branching.Increasing the branch content decreases the rate of secondary nucleation, i ,relative to the rate of surface spreading and so increases the range of supercooling over which regime Ⅰ exists.The rate of bulk crystallization for both isothermal and non\|isothermal crystallization decreases with the increasing of degree of branching.Both Ozawa Equation and Kissinger Equation are invalid for non\|isothermal crystallization kinetics of SCBPE fractions,that means the effects of the branched chain on crystallization process are more complex than expected.