MACROMOLECULES
·
2021
·
IF 5.985
Xuan Li,Lili Wang,Dujin Wang,Alejandro J. Müller,Xia Dong
Successive self-nucleation and annealing (SSA) is an efficient way to thermally fractionate semicrystalline polymers. SSA thermal fractions have distinct melting points corresponding to different lamellar thicknesses. SSA was employed to investigate the in-situ evolution of lamellar thicknesses of polyamide 1012 (PA1012) during high-temperature thermal treatments. A competition between chain growth and crosslinking occurred during the thermal treatments as detected (as a function of time) by SSA, rheology, and dissolution behavior. Based on a master curve of “time–temperature superposition” at a reference temperature, the mechanism for lamellar thickness evolution was divided into three stages: initially, chemical crosslinking predominated. As the number of end groups rapidly increased, linear chain growth and crosslinking occurred simultaneously. Eventually, linear chain growth was increased by chain end-group reactions. The structural changes provoked by the thermal treatments enhanced the mechanical and heat resistance properties of PA1012. This work provides guidance for the design for high-performance polyamide materials.
研究领域:
材料科学
·
高分子化学
✓ 已验证
DOI
高影响因子
CATALYSIS TODAY
·
2020
·
IF 5.825
Junhui Liu,Guanghui Zhang,Xiao Jiang,Junhu Wang,Chunshan Song,Xinwen Guo
Iron-based catalysts have been widely used to synthesize value-added hydrocarbons through CO 2 hydrogenation. Fe carbide, Fe 5 C 2 , was proposed as the active phase responsible for C C coupling during the chain growth. However, the reaction mechanism over iron-based catalysts is still under debate due to the presence of multiple phases of Fe species. In this work, Fe 5 C 2 and K-modified Fe 5 C 2 were prepared and used to study the relationship between the Fe phase, catalytic performance and reaction pathways. CH 4 and CO selectivities of 46.1 C-mol% and 2.8 C-mol% were obtained on Fe 5 C 2 at a CO 2 conversion of 49.8 %, with the main hydrocarbon products being alkanes. With the addition of the promoter K, the C 2 -C 4 = selectivity increased to above 38.0 C-mol%, and the selectivity to C 5+ hydrocarbons increased to 23.9 C-mol% at a similar CO 2 conversion. CH 4 and C 2+ hydrocarbons formed through the CO 2 →CO→hydrocarbons (indirect) route over K-modified Fe 5 C 2 , whereas the direct hydrogenation route occurred on unmodified Fe 5 C 2 in addition to the indirect route of CO 2 to CO to hydrocarbons through Fischer-Tropsch synthesis (FTS) processes. This work offers insights in direct CO 2 hydrogenation over Fe 5 C 2 and Fe 3 O 4 -Fe 5 C 2 catalysts, which advances the understanding of the functions of active phases and reaction pathways of CO 2 hydrogenation over iron-based catalysts.
研究领域:
化学工程
·
催化科学
✓ 已验证
产品关联
DOI
高影响因子
CHEMICAL ENGINEERING JOURNAL
·
2022
·
IF 16.744
Xiaoli Yang,Yalan Wang,Haoxi Ben,Jia Yang,Wei Jiang,Anders Holmen,Yanqiang Huang,De Chen
Fischer–Tropsch synthesis over CoMn oxides is a surface-catalyzed structure-sensitive reaction. Active site changes greatly alter product distribution. The dynamics and essence of the changes in Co species during the reaction have seldom been explored. Herein, multiple characterizations were applied to confirm that two types of active sites, i.e., Co and Co 2 C, coexist on CoMnO x under the reaction conditions. Apart from the direct participation of carbon species in the reaction, the steady-state isotopic transient kinetic analysis also suggested the mutual transformation of carbon species in Co 2 C. The ratio of the two paths altered with the temperature, thus leading to Co 2 C-rich and Co-rich surfaces at intermediate and high temperatures, respectively. Kinetic calculations and microkinetic modeling showed that Co 2 C-rich surfaces facilitated CO adsorption and suppressed hydrogen adsorption. This gave high carbon-chain growth activity. The Co-rich surfaces showed high vacancy and hydrogen coverages, lowering the CO activation and CH 4 formation energies.
研究领域:
催化化学
·
材料科学
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF ELECTROANALYTICAL CHEMISTRY
·
2023
·
IF 4.5
Jie Jiang,Ziying Hong,Zhiyuan Qiao,Qianlong Zhu,Hong Zhang,Yanxiao Jiang,Kai Yu
It has been a challenge to accurately characterize the chain growth mechanism during copolymerization. Herein, an electrochemistry-microtube-mass spectrometry (EC-mTube-MS) was developed for on-line monitoring of aniline (ANI) electro-copolymerized with o-phenylenediamine (oPD). Short-lived intermediates and co-oligomers belonging to polyANI-oPD were structural identified with tandem MS method for the first time. The free binding between ANI and oPD monomers determined the presence of more species for a given co- n -mer. Chain growth was found to compete with 2H + , 2e − intramolecular oxidation of co-oligomers, resulting in the units with quinone or phenazine structures. MS signals for polyANI and polyoPD were observed as well, indicating that the homopolymerization occurred simultaneously with the copolymerization, which may affect the formation efficiency even performance of the final copolymer. Investigations on the monomer feed ratio and solution pH provided data support for improving the copolymerization efficiency, and the recommended parameters are c ANI : c oPD ≥ 10:1 and pH = 7.
研究领域:
材料科学
·
分析化学
✓ 已验证
产品关联
DOI
高影响因子
Surfaces and Interfaces
·
2024
·
IF 5.7
Manli Zhou,Taishun Zhang,Bao Zhang,Xiaohong Peng
Anti-glare coatings offer a promising solution for mitigating light pollution, with the construction of a rough surface being essential to their effectiveness. In this paper, a series of waterborne polyurethane (WPU) coatings with self-antiglare effect were successfully synthesized by adjusting the molar ratio of the post-chain extenders sodium N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonate (BES) and hydrazine hydrate (N 2 H 4 ). This approach utilized BES as a post-chain extender for the first time, resulting in a double micro-rough surface structure that enabled the coating to achieve better anti-glare effect with relatively lower roughness. The effects of BES and N 2 H 4 on particle size, morphology, gloss, zeta potential, transmittance, and hydrophilicity of WPU were investigated. When the BES content accounted for 30 mol% of the post-chain extenders, the average particle size of the emulsion was 1321.4 nm, and the 60° gloss of the coating was 36.1 GU. Additionally, we thoroughly analyzed the formation mechanism of the “worm-like” micro-rough structure on the surface of latex particles. The strongly hydrophilic -SO 3 − Na + groups in the emulsion pulled the molecular chains to extend to the outer layer of the latex particles. Upon water evaporation, these molecular chains curled up on the particle surfaces, forming a "worm-like" micro-rough structure. XRD spectrum, FBI-SEM, and TEM images confirmed that this micro-rough structure was formed by self-assembly on the particle surface rather than internal crystallization. This finding provides novel insights into the development of self-antiglare WPU coatings characterized by intricate rough surfaces. Furthermore, it contributes to the advancement of surface and interface science through improved performance of WPU coatings.
研究领域:
材料科学
·
界面化学
·
高分子化学
✓ 已验证
产品关联
DOI
高影响因子
Polymer Chemistry
·
2015
·Vol. 7
·期 4
·860-866
·
IF 5.52
Hongyuan Wang,Rongqi Zhu,Po Yang,Yi Gu
The chain propagations of Bisphenol A-aniline benzoxazine (defined as BA-a) polymerized by thermal induction and in the presence of various catalysts or curing agents during the curing process before gelation were investigated in this paper. DSC, gel time test and GPC were used to measure the curing behavior, number-average molecular weight (n), glass transition temperature (Tg), gel time (tgel) and curing conversion (α) of different benzoxazine systems. By comparing the experimental results (n and Tg) with the models of step polymerizations and chain polymerizations proposed by Flory et al., three kinds of chain propagations of benzoxazine were observed and confirmed. The step polymerization occurred in the thermal induction or in the presence of catalyst N,N-dibenzylaniline (tAm), and then the non-living chain polymerization and the living chain polymerization occurred, respectively, when indole (Id) and other additives such as phenol (tBp), acid (HA), imidazole (IMZ) etc. were added to benzoxazine as catalysts or curing agents. Moreover, the relationship between the chain propagation and curing kinetics of benzoxazine was also established. The chain propagation of benzoxazine systems involves step polymerization, non-living chain polymerization andliving chain polymerization, the conversion of the gel point (αgel) is almost equal to, less than and greater than the value of the conversion at which the polymerization rate reaches a maximum (αmax), respectively. The results may contribute to a better understanding of the polymerization mechanism of benzoxazine and provide new approaches to effective control of the polymerization kinetics and growth crosslink structures of benzoxazine.
研究领域:
材料科学
·
化学工程
✓ 已验证
产品关联
DOI
高影响因子
ACS Catalysis
·
2020
·
IF 12.35
Yaru Zhang,Xiong Su,Lin Li,Haifeng Qi,Chongya Yang,Wei Liu,Xiaoli Pan,Xiaoyan Liu,Xiaofeng Yang,Yanqiang Huang,Tao Zhang
The Ru/TiO2 catalyst serves as a representative metal/support interaction system with tunable reactivity in catalytic processes. Herein, by varying the metal loadings of Ru from 0.5 to 4 wt % to regulate the size of Ru on support, the catalytic performances of Ru/TiO2 catalysts in Fischer–Tropsch synthesis (FTS) can be further refined. An improved FTS activity is acquired when metal size increases, while long carbon-chain products (C5+ hydrocarbons) prefer to be generated from the small-sized Ru catalyst. With intensive characterizations, it is indicated that the coating of TiOx on Ru greatly depends on the size of Ru, with the TiOx overlayer being enhanced on small Ru metal particles. This size-dependent metal/support interaction on Ru/TiOx therefore leads to a varied reduction degree of Ru, which possesses an alterable capability toward CHx transformation on Ru. As a result, the small-sized Ru/TiOx catalyst shows a preference toward the chain growth in FTS by suppressing the competitive methanation on Ru/TiOx. Our results demonstrate that the size-dependent metal/support interaction plays an important role on determining the catalytic performance of Ru/TiOx in FTS, and it can be used as an effective method to tune the reactivity of metal nanoparticles in catalytic processes.
研究领域:
催化化学
·
材料科学
✓ 已验证
DOI
高影响因子
MACROMOLECULAR RAPID COMMUNICATIONS
·
2024
·Vol. 45
·期 19
·2400259
·
IF 4.2
Zhihao Niu,Yimin Wang,Xin Wang,Dexian Yin,Tao Shou,Pengfei Cao,Xiuying Zhao,Shikai Hu,Liqun Zhang
The thermodynamic incompatibility between the soft and hard segments of thermoplastic polyurethane (TPU) results in a microphase-separated behavior and excellent mechanical properties. However, the effect of the chain extender on the degree of microphase separation (DMS) and the resultant mechanical properties of TPU have not been well studied because of the complex interactions between the soft and hard segments. Herein, hydroxyl-terminated polybutadiene-based TPUs(HTPB-TPUs) without hydrogen bonding between the soft and hard segments are synthesized using hydroxyl-terminated polybutadiene, toluene diisocyanate, and four different chain extenders, and the effect of the chain extender structure on DMS is analyzed experimentally using a combination of analytical techniques. Furthermore, the solubility parameters of the soft and hard segments, glass transition temperatures, and hydrogen-bond density of the HTPB-TPUs, are computed using all-atom molecular dynamics simulations. The results clearly reveal that the chain extender significantly affects the DMS and thus the mechanical properties of HTPB-TPUs. This study paves the way for studying the relationship between the structure and properties of TPU.
研究领域:
材料科学
·
高分子化学
✓ 已验证
产品关联
DOI
PubMed
高影响因子
RSC Advances
·
2015
·Vol. 5
·期 40
·31878-31885
·
IF 3.84
Alvianto Wirasaputra,Jianqing Zhao,Yaming Zhu,Shumei Liu,Yanchao Yuan
Chain scission of polyamide-6 (PA6) takes place readily during high temperature processing. To prevent possible deterioration in its properties, chain extension of PA6 by the use of bis(glycidyloxy)phenylphosphine oxide (BGPPO), a traditional small molecule flame retardant, has been evaluated in the present study. It was found that the melting torque of PA6 modified by 2.5 minutes' mixing with 1.5 wt% BGPPO was about seven times higher than that of unmodified PA6. As a result of the modification, the proportion of amino and carboxyl end-groups of PA6 was greatly decreased. Accordingly, the tensile, flexural and notched Izod impact strength of the chain-extended PA6 were correspondingly increased, the improvement being superior to that produced using a commercial chain extender. The use of BGPPO for this purpose exemplifies its multifunctional characteristics.
研究领域:
材料科学
·
高分子化学
✓ 已验证
产品关联
DOI
高影响因子
ACS Catalysis
·
2016
·
IF 9.307
Jie Sun,Qiuxia Cai,Yan Wan,Shaolong Wan,Li Wang,Jingdong Lin,Donghai Mei,Yong Wang
The promotional effects of a cesium promoter on higher alcohol (C2+OH) synthesis from syngas over Cs2O-Cu/ZnO/Al2O3 catalysts were investigated using a combined experimental and density functional theory (DFT) calculation method. In the presence of a cesium promoter, the C2+OH productivity increases from 77.1 to 157.3 g kgcat–1 h–1 at 583 K due to the enhancement of the initial C–C bond formation. A detailed analysis of chain growth probabilities (CGPs) confirms that initial C–C bond formation is the rate-determining step in the temperature range of 543–583 K. Addition of a cesium promoter significantly increases the productivities of 2-methyl-1-propanol, while the CGP values (C3* to 2-methyl-C3*) are almost unaffected. With the assistance of a cesium promoter, the CGPs of the initial C–C bond formation step (C1* to C2*) increase from 0.13 to 0.25 at 583 K. DFT calculations indicate that the initial C–C bond formation during syngas synthesis over the ZnCu(211) model surface is mainly due to the HCO + HCO coupling. In the presence of Cs2O, the stabilities of key intermediates such as HCO and H2CO are enhanced, which facilitates both HCO + HCO and HCO + H2CO coupling steps with lower activation barriers. In addition, Bader charge analysis suggests that the presence of cesium ions could facilitate nucleophilic coupling between HCO and H2CO for the initial C–C bond formation.
研究领域:
催化化学
·
能源化学
·
理论化学
✓ 已验证
产品关联
DOI
高影响因子
Molecular Catalysis
·
2019
·
IF 2.938
Xinli Tong,Zhenya Zhang,Yiqi Gao,Yue Zhang,Linhao Yu,Yongdan Li
A novel carbon-chain increasing valorization of furfural (FUR), a cheap bio-based platform compound, has been successfully performed via the catalytic oxidative condensation process with mono-dispersed palladium oxide catalyst. For the reaction of furfural, n-propanol and O 2 , the PdO@TiO 2 exhibited a prominent catalytic activity in which a 77.8% conversion of FUR with 89.2% selectivity of 3-(furan-2-yl)-2-methylacrylaldehyde was obtained. Based on the XRD, SEM, TEM, HRTEM, XPS, and UV–vis results of catalysts, it was concluded that high activity is associated with particle size, uniform distribution of palladium oxide and surface area of the support. Moreover, the recycling experiments confirmed that mono-dispersed palladium oxide catalyst was stable, in which it still kept a good catalytic performance after being recycled for five times. This provided a new route for the selective transformation of the hemicellulose-derived platform compounds.
研究领域:
催化化学
·
可再生化学
·
材料科学
✓ 已验证
产品关联
DOI
高影响因子
INORGANICA CHIMICA ACTA
·
2018
·
IF 2.264
Feng He,Dan Wang,Baiyu Jiang,Zhen Zhang,Zhenmei Cheng,Zhisheng Fu,Qisheng Zhang,Zhiqiang Fan
A novel α-diimine nickel pre-catalyst Cat.1 with two electron-donating methyl substituents on the ligand backbone was synthesized and investigated for ethylene polymerization using methylaluminoxane as cocatalyst. Cat.1 exhibited higher polymerization activity and produced highly branched polyethylene with slightly higher molecular weight than that of the typical Brookhart catalyst ( B-Cat ) at elevated temperature. By tracing the changes of active center number in the polymerization process, Cat.1 was found to have higher ratio of activated nickel ([C ∗ ]/[Ni]), longer catalyst lifetime and larger chain propagation rate constant ( k p ) as compared with B-Cat . The computational studies demonstrated the electron-donating methyl substituents can make a more electron-rich ligand to influence the catalytic properties of Cat.1 . Stronger interactions between the electron-rich ligand and the nickel center should be the main reasons for longer catalyst lifetime and enhanced thermal stability of Cat.1 . The production of polyethylene with higher molecular weight by Cat.1 can be explained by its larger k p value and more stable transition state for ethylene insertion than for chain transfer reaction due to the electron-donating ligand. Overall, the results of this work clearly support the importance of ligand electronic effects on the thermal stability and intrinsic reactivity of active centers in α-diimine Ni(II) catalysts.
研究领域:
高分子化学
·
催化化学
✓ 已验证
产品关联
DOI
高影响因子
危险品化学品经营许可证（带存储）