Influence of n-alkyl branches on glass-transition temperatures of branched polyethylenes prepared by means of metallocene- and palladium-based catalysts

被引:62
作者
Mäder, D
Heinemann, J
Walter, P
Mülhaupt, R
机构
[1] Univ Freiburg, Freiburger Mat Forschungszentrum, D-79104 Freiburg, Germany
[2] Univ Freiburg, Inst Makromol Chem, D-79104 Freiburg, Germany
关键词
D O I
10.1021/ma991096o
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
Branched polyethylenes with controlled molecular architectures were prepared by means of metallocene-catalyzed copolymerization of ethylene with l-olefins such as propylene, l-butene, l-hexene, and 1-octene and by means of migratory-insertion-type ethylene homopolymerization using methylpalladium diazadiene berate as catalyst. Glass-transition temperatures, T-g, as determined by means of dynamic mechanical analysis (DMA), were correlated with propylene and l-butene weight fractions of ethylene copolymers over the entire composition range. Several correlations between degree of branching and T-g were evaluated for ethylene-rich copolymers and branched ethylene homopolymers. The conventional degree of branching is defined as the number of branched tertiary C atoms per 1000 C atoms of the methylene units or 1000 C atoms of the entire polymer chain. We propose a new degree of branching that is defined as sum of the number of branched tertiary C atoms in the polyethylene chain and the C atoms of the n-alkyl branch, referred to 1000 C atoms of the polyethylene backbone, that gives excellent correlation with T-g of branched polyethylene, independent of the branch type and the synthetic route used to prepare branched polyethylene.
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页码:1254 / 1261
页数:8
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