Molecular weight distribution shape approach for simultaneously enhancing the stiffness, ductility and strength of isotropic semicrystalline polymers based on linear unimodal and bimodal polyethylenes

• Published in: Polymer (Guilford) Vol. 275; p. 125936
• Main Authors: Long, Chuanjiang, Dong, Zhen, Wang, Keqiang, Yu, Feng, He, Chaobin, Chen, Zhong-Ren
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 09.05.2023
• Subjects: Bimodal; Mechanical properties; Molecular weight distribution shape; Unimodal; Mechanical properties; Bimodal; Molecular weight distribution shape; Unimodal
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2023.125936

Bimodal polyethylenes (PEs) have captured broad attention in recent years, while little is known about the contribution of bimodal molecular weight distribution (MWD) shape on their properties compared with unimodal MWD shape. In this work, a comparative investigation of MWD shape-mechanical property relationship of isotropic semicrystalline polymers based on linear unimodal and bimodal PEs has been carried out. This first systematic study indicates that MWD shape influences the chain arrangements in crystalline and amorphous phases which affect their mechanical performance. PEs with bimodal shape exhibit higher crystallinity, lower entanglements and higher fraction of tie molecules than unimodal shape, contributing to simultaneously enhanced Young's modulus, yield strength, elongation at break and tensile strength. This work demonstrates that the modulation of MWD from unimodal to bimodal shape could overcome the trade-off among stiffness, strength and ductility of semicrystalline polymers without altering chain structure, chemical composition or average molecular weight. [Display omitted] •Linear unimodal and bimodal polyethylenes (PEs) with well-defined molecular weight distribution (MWD) shape are used as a polymer model system to study the MWD shape-mechanical property relationship of isotropic semicrystalline polymers.•Compared to unimodal PEs at the same weight-average molecular weight, compression-molded bimodal PEs have higher crystallinity, thinner and denser packed lamellae, higher fraction of tie molecules (n > 3) and lower entanglements in amorphous phase. A mechanism is proposed to explain the MWD shape dependence of crystalline and amorphous phase structure.•Due to the higher crystallinity, lower entanglements in amorphous phase and higher fraction of tie molecules, compression-molded bimodal PEs show simultaneously enhanced Young's modulus, yield strength, elongation at break and tensile strength than unimodal PEs at comparable molecular weight.