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Dominant Effects of Short-Chain Branching on the Initial Stage of Nucleation and Formation of Tie Chains for Bimodal Polyethylene as Revealed by Molecular Dynamics Simulation

1
Shanghai Key Laboratory of Multiphase Material Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China
2
College of Materials and Energy, South China Agricultural University, Guangzhou 510642, China
*
Authors to whom correspondence should be addressed.
Polymers 2019, 11(11), 1840; https://doi.org/10.3390/polym11111840
Received: 9 October 2019 / Revised: 1 November 2019 / Accepted: 5 November 2019 / Published: 8 November 2019
(This article belongs to the Section Polymer Theory and Simulation)
The molecular mechanism of short-chain branching (SCB), especially the effects of methylene sequence length (MSL) and short-chain branching distribution (SCBD) on the initial stage of nucleation, the crystallization process, and particularly the tie chain formation process of bimodal polyethylene (BPE), were explored using molecular dynamics simulation. This work constructed two kinds of BPE models in accordance with commercial BPE pipe resins: SCB incorporated in the long chain or in the short chains. The initial stage of nucleation was determined by the MSL of the system, as the critical MSL for a branched chain to nucleate is about 60 CH2. SCB incorporated in the long chain led to a delay of the initial stage of nucleation relative to the case of SCB incorporated in the short chains. The increase of branch length could accelerate the delay to nucleation. The location of short chain relative to the long chain depended on the MSL of the short chain. As the MSL of the system decreased, the crystallinity decreased, while the tie chains concentration increased. The tie chains concentration of the BPE model with branches incorporated in the long chain was higher than that with branches incorporated in the short chain. View Full-Text
Keywords: short-chain branching distribution; methylene sequence length; bimodal polyethylene; molecular dynamics simulation; crystal nucleation; tie chains short-chain branching distribution; methylene sequence length; bimodal polyethylene; molecular dynamics simulation; crystal nucleation; tie chains
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MDPI and ACS Style

Hu, Y.; Shao, Y.; Liu, Z.; He, X.; Liu, B. Dominant Effects of Short-Chain Branching on the Initial Stage of Nucleation and Formation of Tie Chains for Bimodal Polyethylene as Revealed by Molecular Dynamics Simulation. Polymers 2019, 11, 1840.

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