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Precise modulation of molecular weight distribution for structural engineering.

ABSTRACT: As one of the most critical molecular parameters, molecular weight distribution has a profound impact on the structure and properties of polymers. Quantitative and comprehensive understanding, however, has yet to be established, mainly due to the challenge in the precise control and regulation of molecular weight distribution. In this work, we demonstrated a robust and effective approach to artificially engineer the molecular weight distribution through precise recombination of discrete macromolecules. The width, symmetry, and other characteristics of the distribution can be independently manipulated to achieve absolute control, serving as a model platform for highlighting the importance of chain length heterogeneity in structural engineering. Different from their discrete counterparts, each individual component in dispersed samples experiences a varied degree of supercooling at a specific crystallization temperature. Non-uniform crystal nucleation and growth kinetics lead to distinct molecular arrangements. This work could bridge the gap between discrete and dispersed macromolecules, providing fundamental perspectives on the critical role of molecular weight distribution.

SUBMITTER: Tan R

PROVIDER: S-EPMC7003969 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Precise modulation of molecular weight distribution for structural engineering.

Tan Rui R Zhou Dongdong D Liu Baolei B Sun Yanxiao Y Liu Xinxin X Ma Zhuang Z Kong Deyu D He Jinlin J Zhang Zhengbiao Z Dong Xue-Hui XH

Chemical science 20191029 46

As one of the most critical molecular parameters, molecular weight distribution has a profound impact on the structure and properties of polymers. Quantitative and comprehensive understanding, however, has yet to be established, mainly due to the challenge in the precise control and regulation of molecular weight distribution. In this work, we demonstrated a robust and effective approach to artificially engineer the molecular weight distribution through precise recombination of discrete macromol ...[more]

PMID: 32055380

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Project description:The present study aimed to identify the required characteristics of binder pitches in the filler-binder mixing process to effectively manufacture graphite blocks. To this end, a binder pitch was separated into pitch fractions of varying molecular-weight segments. The role and effectiveness of each pitch fraction were then analyzed with respect to their molecular-weight distribution. As a result, the optimal molecular-weight distribution was determined. More specifically, a coal-tar pitch was separated into solvent-soluble and solvent-insoluble fractions. The molecular-weight distribution was determined according to this classification, and the characteristics of each pitch fraction were examined. The pitch separation process was conducted using three solvents: hexane, toluene, and quinoline. The resulting pitch was separated into the following pitch fractions: hexane-soluble (HS), hexane-insoluble-toluene-soluble (HI-TS), toluene-insoluble-quinoline-soluble (TI-QS), and quinoline-insoluble (QI). Fourier transform infrared (FT-IR) spectrum, matrix-assisted laser desorption ionization-time of flight (MALDI-TOF), and softening point of each pitch fraction were measured. Also, pitch samples were refabricated while varying the mixing ratio of these pitch fractions, and carbon blocks were then prepared using them. The compressive strength and porosity of these blocks were measured and compared. The P154_B pitch with a high content of TI-QS was used to fabricate a green block. Due to the high viscosity of the binder used, the fluidity was not sufficiently high, and thus, the green block made of this pitch had relatively low strength. The other blocks had similar levels of strength. After the carbonization process, the carbon block with a high content of HS (P352_B-C) and the carbon block with the HS content removed (P073_B-C) showed lower compressive strength than their respective green-block counterparts (P352_B and P073_B). However, their strength was higher compared to those of the other carbon blocks. In the case of carbon block P073_B-C, the HS content was completely removed, and thus, the content of TI-QS (β-resin) was relatively high. Accordingly, this carbon block ended up with large amounts of components that had high coking values (CVs), and this contributed to limiting the formation of pores. Therefore, the compressive strength of this carbon block was high. In the case of the carbon block with a high content of HS (P352_B-C), a suitable level of viscosity was achieved because the HS components ensured high fluidity. As a result, blocks with higher density and compressive strength could be fabricated. The major findings of the present study confirm that producing carbon blocks with high mechanical properties requires binder pitches with a balanced combination of suitable viscosity to ensure sufficiently high fluidity and a proper level of CV to effectively suppress the formation of pores in the mixing and molding process.

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Precise modulation of molecular weight distribution for structural engineering.

Publications

Precise modulation of molecular weight distribution for structural engineering.

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