期刊
POLYMER
卷 112, 期 -, 页码 43-52出版社
ELSEVIER SCI LTD
DOI: 10.1016/j.polymer.2017.01.076
关键词
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资金
- National Science Foundation of China [21574086]
- Nanshan District Key Lab for Biopolymers and Safety Evaluation [KC2014ZDZJ0001A]
- Shenzhen Sci & Tech research grant [ZDSYS201507141105130]
- Shenzhen City Science and Technology Plan Project [JCYJ20140509172719311]
Unbridged oscillatory metallocenes are prone to produce heterogeneous chain microstructure, for instance, giving rise to elastomeric polypropylene. Here, we use the bis(2-phenylindenyl)ZrCl2/MAO catalyst system, featuring oscillating ligands, to copolymerize ethylene with several a alpha-olefins. Through investigation of chain microstructure, thermal and rheological properties, we show that the complex behavior of these materials can be justified by considering a catalyst with dual active center having different comonomer affinities. This behavior is consistent with the proposed mechanism of fast oscillating ligands, becoming locked upon proximity of cocatalyst counteranion, leading to diverse stereo and comonomer selectivity. The unlocked, oscillating active center with lower comonomer response gives rise to mostly linear chains and is not affected by the presence of comonomer, while the locked one creates long chain branched chains, whose frequency decreases by introduction of comonomer. Copolymer samples exhibited bimodal MWD, dual crystallization mechanisms, and low frequency plateau modulus, specifically at higher comonomer levels. It was concluded that the overall behavior is determined by complex interplay of SCB and LCB, which leads to thermorheological complexity as well as phase separation. (C) 2017 Elsevier Ltd. All rights reserved.
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