期刊
ACS APPLIED POLYMER MATERIALS
卷 5, 期 4, 页码 2654-2663出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsapm.2c02236
关键词
unimodal; bimodal; MWD; MWD shape; crystallization kinetics; polyethylene
In this study, the impact of bimodal molecular weight distribution (MWD) shape on the crystallization kinetics of semicrystalline polymers was investigated. It was found that polyethylenes (PEs) with a bimodal shape exhibited faster nucleation and crystallization rates with smaller lamellar width at low temperatures. The higher crystallization enthalpy of bimodal PEs was also demonstrated, and the mechanism behind this was explained.
The manipulation of the crystallization kinetics and crystallinity of polymers without altering their chemical composition, chain structure, or average molecular weight is challenging, while little attention is paid to the role of molecular weight distribution (MWD) shape. In this work, a series of welldefined linear unimodal and bimodal polyethylenes (PEs) with molecular weights ranging from 300 k to 1200 k g/mol were synthesized to serve as a model system to study the impact of bimodal MWD shape on the crystallization kinetics of semicrystalline polymers in comparison with unimodal MWD shape at the same weight-average molecular weight (Mw). It is shown that PEs with a bimodal shape exhibit a faster nucleation rate and crystallization rate with a smaller lamellar width at low isothermal temperatures. A higher crystallization enthalpy of bimodal PEs is shown in non-isothermal experiments. The mechanism behind this is elucidated, which suggests that MWD shapes mainly affect the small-scale nucleation process without altering the large-scale growth process. This first systematic comparative study on the crystallization kinetics of linear unimodal and bimodal PEs gives insight into tailoring the crystallization behavior of semicrystalline polymers from an MWD shape perspective.
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