Physical gelation of crystallizing metallocene and Ziegler-Natta ethylene-hexene copolymers

被引:18
作者
Gelfer, M
Horst, RH
Winter, HH [1 ]
Heintz, AM
Hsu, SL
机构
[1] Univ Massachusetts, Dept Polymer Sci & Engn, Amherst, MA 01003 USA
[2] Univ Massachusetts, Dept Chem Engn, Amherst, MA 01003 USA
关键词
gelation; crystallization kinetics; polyethylene;
D O I
10.1016/S0032-3861(03)00077-6
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
The effect of molecular architecture on the evolution of viscoelastic properties during crystallization was investigated using ethylene-hexene copolymers manufactured via metallocene (M-LLDPE) and Ziegler-Natta (ZN-LLDPE) processes. Differences in branching distribution were shown to have a drastic effect on the viscoelastic properties near the gel point. It is shown that the branching distribution rather than branch content is the determining parameter for the evolution of the rheological properties during isothermal and non-isothermal crystallization, and for the width of the solidification interval. We developed a partial melting technique for the preparation of stable critical gels of LLDPE whose viscoelastic properties correspond to the intermediate state between melt and solid. Local molecular conformation and crystallinity in these gels were characterized by Raman spectroscopy, which shows that the transition from melt-like to solid-like rheological behavior (physical gelation) in LLDPE occurs at a very low overall crystallinity of less than 5%. (C) 2003 Elsevier Science Ltd. All rights reserved.
引用
收藏
页码:2363 / 2371
页数:9
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