POLYMER
·
2011
·
IF 3.829
Muhammad Naveed Anjum,Lihua Zhu,Zhihong Luo,Jingchun Yan,Heqing Tang
Optically active polyorthoanisidine, polyorthotoluidine, polyorthoethylaniline and polyorthochloroaniline were synthesized with chemical polymerization of corresponding monomers in aqueous medium by using d - or l -camphorsulfonic acid ( d - or l -CSA) as chiral dopant , ammonium persulfate as oxidant, and diaminodiphenylamine as initiator. By circular dichroism spectroscopic measurements, it was found that PANI exhibited generally a reversed chirality in comparison with the used chiral dopant, but the substituted PANIs had the same one as the chiral dopant. This revealed that the substituent at ortho position caused helical inversion of conformation in comparison with the parent PANI. Such effect was further confirmed by the influence of the copolymerization of aniline and its derivatives on the chirality of the copolymers . The effect of the substituent on the chirality of the copolymers was increased with the increase of the steric hindrance of the ortho substituent. A mechanism was proposed to explain the effects of steric hindrance on the chirality of PANIs. The clarified relationship between the steric hindrance and the chirality of the polymer can enable us to tailor the chiroptical properties of functional polymer materials for future application.
研究领域:
高分子化学
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材料科学
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产品关联
DOI
高影响因子
CHEMICAL ENGINEERING JOURNAL
·
2023
·
IF 15.1
Hongyu Niu,Xing-Bao Wang,Jingjie Luo,Jiaxin Liu,Chuang Li,Wen-Ying Li,Changhai Liang
Desulfurization plays a critical role in refining crude oil to produce fuel and the manufacture of fine chemicals. However, its low efficiency becomes a great challenge for the present desulfurization if only the C-S cleavage is considered a promising approach to reducing hydrogen consumption under atmospheric pressure. Accordingly, we investigate the critical factors necessary to achieve high C-S cleavage of dibenzothiophenes under mild conditions of 0.1 MPa and H 2 /oil = 100. The mechanism of reactive adsorption desulfurization of dibenzothiophenes with or without steric hindrance at atmospheric pressure on Pt/ZnO is proposed by studying the adsorption model of active metal sites, the Pt efficiency in C-S cleavage influenced by the steric hindrance and the structural evolution of Pt active centers in the presence of sulfur adsorption/deposition. Based on both experimental and DFT results, we report C-S cleavage of dibenzothiophenes with (TOF = 15 h −1 ) or without steric hindrance (TOF = 128 h −1 ) that can be highly efficiently fractured (99.9%) by the interface between PtS x and ZnO . This work has great practical significance for developing atmospheric industrial adsorbents for ultra-deep reactive adsorption desulfurization.
研究领域:
化学工程
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催化材料
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能源化工
✓ 已验证
产品关联
DOI
高影响因子
EUROPEAN POLYMER JOURNAL
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2019
·
IF 3.621
Qi Wu,Xiaoru Ma,Feng Zheng,Xuemin Lu,Qinghua Lu
Highly transparent polyimides (PIs) with excellent combined properties are in great demand for flexible optical devices. In this work, transparent PIs were synthesized by fluorinated aromatic dianhydride ( 6FDA ) and three aromatic diamines containing methyl side groups with different amount and position. These PIs possessed moderate to great optical transparency and excellent solubility. With four methyl groups at 2,2′,5,5′-position in diamine, 2255TMB–PI exhibited the best transmittance up to 82% at 400 nm. In all cases, PIs were determined to have low dielectric constants (2.84–2.99) and high glass transition temperature (above 390 °C, even up to 407 °C for 2255TMB–PI ). In addition, the toughness of these PI films was also proven by a tensile strength of 130 – 156 MPa. In spite of the electron donating character of methyl groups, their steric hindrance was found to have significant effect on the combination properties of PIs. Spatial structures and packing morphology are thought to be the main contribution. Therefore, this work provided an easy way to prepare highly transparent polyimides with excellent combined properties by controlling steric hindrance through methyl side groups.
研究领域:
材料科学
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化学工程
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产品关联
DOI
高影响因子
JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY
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2012
·Vol. 50
·期 15
·3149-3157
·
IF 3.919
Ning Ren,Xiao-Jun Huang,Xu Huang,Yue-Cheng Qian,Cang Wang,Zhi-Kang Xu
We describe a versatile approach to synthesize glycosylated polyphosphazenes with controllable density of glycosyl groups. These glycopolymers have been synthesized by the nucleophilic substitution of poly(dichlorophosphazene) with propargylamine and subsequent “thiol–yne” click reaction between poly[di(propargylamine)phosphazene] and 2,3,4,6-tetra- O -acetyl-1-thio-β- D -glucopyranose (SH-GlcAc 4 ). The polymers were characterized with FTIR and 1 H NMR. We found that the high steric hindrance of SH-GlcAc 4 plays a key role in the overall reaction process, and ∼55% of the alkyne groups participate in the “thiol–yne” click reaction. About 8% of the alkyne groups convert to alkene groups at the end of click reaction. The substitution of alkyne/alkane mixture was conducted to reduce the alkyne density in the side groups of polyphosphazenes and minimize the influences of this steric effect. Mixed-substituent polyphosphazene was synthesized with 2:3 ratio of alkyne and alkane. In this case, almost no alkyne group remains after the “thiol–yne” click reaction, and thus the glycosylated polyphosphazene is able to form into micelles through self-assembly process. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
研究领域:
高分子化学
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生物材料学
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产品关联
DOI
高影响因子
JOURNAL OF APPLIED POLYMER SCIENCE
·
2023
·Vol. 140
·期 23
·e53931
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IF 3
Zhenzhong Li,Tianfeng Zhou,Hai Liu,Yu Jin,Yuxia Pang,Hongming Lou,Dongjie Yang,Xueqing Qiu
The steric hindrance formed by polyether side chains is the key factor determining the dispersion performance of polycarboxylate superplasticizer (PCE). While with the increase of the side chain length, the coiled conformation of side chain will prevent the dispersion ability of PCE from being further improved. In this work, the methallyl polyoxyethylene ether (HPEG) was esterified with tricarballylic acid (TA) to obtain dicarboxyl terminated macromonomer, and further used to synthesize polycarboxylate (PCETA). The fluidity tests show that compared with ordinary PCE-B2400 with short side chain, the dispersion performance of PCETA-2400 was slightly improved. While for the PCEs with long side chain, the dispersion ability of PCETA-4000 was significantly improved than that of ordinary PCE-B4000. The adsorption layer thickness of PCETA-4000 adsorbed on the surface of SiO 2 sphere measured by dynamic light scattering is 7.93 nm, which is 1.3 times that of PCE-B4000. Due to electrostatic repulsion between the carboxylic groups, the stretching of long side-chain forms stronger steric hindrance and enhancing the dispersion of cement particles. In addition, PCETA also shows good slump retention and clay resistance properties, and it is an excellent multi-functional concrete admixture with great application potential.
研究领域:
建筑材料化学
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胶体化学
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产品关联
DOI
高影响因子
RSC Advances
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2022
·Vol. 12
·期 55
·35508-35516
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IF 4.036
Wenlin Shuai,Shiwei Wang,Taotao Sun,Hongfeng Yin,Yu Zu,Gang Yao,Zhonghua Li,Zhaokun Qi,Mei Zhong
Dispersants can have a substantial impact on the rheological characteristics of coal–water slurry (CWS). Due to their advantages in cost and synthesis, linear dispersants are currently most often employed in the commercial manufacturing of CWS. However, this kind of dispersant gives limited performance because of its weak adsorption and steric hindrance effect on the coal–water interface. This work describes a new linear dispersant (PSAF) with a significant steric hindrance effect that was created by incorporating phenolic groups into its molecular architecture, which gives higher maximum coal content (63.79 wt%) than that (63.11 wt%) from sulfonated acetone–formaldehyde (SAF). The synthesis mechanism was investigated using GPC, FT-IR and NMR. Various technologies were used to explore the rheological characteristics and dispersion mechanism for CWS prepared with PSAF. PSAF as well as SAF showed monolayer adsorption on the surface of coal and displayed a higher adsorption layer thickness (3.5 nm). PSAF dispersant presents stand-up adsorption rather than lie-down adsorption of SAF because of its strong π–π action, resulting in a stronger steric hindrance effect and improved rheological performance. This work can provide guidelines for the development of a high-performance dispersant as well as an understanding of the dispersal process for CWS.
研究领域:
材料科学
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化学工程
✓ 已验证
产品关联
DOI
PubMed
高影响因子
JOURNAL OF LUMINESCENCE
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2019
·
IF 2.961
Qiuhong Wang,Ming Xu,Wei Feng,Fuyou Li
Upconversion based on triplet-triplet annihilation (TTA-UC) has received much attention due to its unique ability to effectively harvest low-energy photons in the solar spectrum for widespread investigations involving energy, environment, and bioapplication. However, the utilization of conventional TTA-UC systems for low-power bioimaging in vivo is still a challenge due to their incompatibility and moderate efficiency in aqueous media. Herein, we pioneer the molecular modification strategy by introducing steric hindrance to the BODIPY annihilators to realize robust TTA-UC in biocompatible nanocapsule . The improved molecules could maintain excellent luminescence even at a very high concentration wherein the separation distance between neighbouring chromophores was reduced to facilitate the pivotal process of Dexter energy transfer. In this way, the encapsulated TTA-UC system became highly efficient in biological circumstance with quantum efficiency Ф UC of 6.3%. Consequently, the constructed nanocapsule was capable of operating at low-power with high contrast for in vivo imaging.
研究领域:
生物化学
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材料科学
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医学影像学
✓ 已验证
产品关联
DOI
高影响因子
Polymers
·
2019
·Vol. 11
·期 5
·826
·
IF 3.164
Chengguo Liu,Qiong Wu,Rongrong An,Qianqian Shang,Guodong Feng,Yun Hu,Puyou Jia,Yonghong Zhou,Wen Lei
New tung oil (TO)-based, unsaturated, co-ester (Co-UE) macromonomers bearing steric hindrance were synthesized by modifying a TO-based maleate (TOPERMA) monomer with an anhydride structure with hydroxyethyl methacrylate (HEMA) and methallyl alcohol (MAA), respectively. The obtained Co-UE monomers (TOPERMA-HEMA and TOPERMA-MAA) were then characterized by1H NMR and gel permeation chromatography (GPC). For comparison, hydroxyethyl acrylate (HEA)-modified TOPERMA (TOPERMA-HEA) was also synthesized and characterized. Subsequently, the obtained Co-UEs were thermally cured with styrene, and the ultimate properties of the resulting materials were studied. It was found that by introducing the structure of steric hindrance into the TO-based Co-UE monomer, the tensile strength and Young’s modulus of the resulting materials were improved. Furthermore, by reducing the length of the flexible chain in the Co-UE monomer, the tensile strength, Young’s modulus, and glass transition temperature (Tg) of the resultant materials were also improved. The TOPERMA-MAA resin gave the best performance in these TO-based Co-UE resins, which showed a tensile strength of 32.2 MPa, Young’s modulus of 2.38 GPa, andTgof 130.3 °C. The developed ecofriendly materials show promise in structural plastic applications.Keywords:tung oil;unsaturated polyester resins;thermosetting polymers;structure–property relationship;structural plastics
研究领域:
材料科学
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高分子化学
✓ 已验证
DOI
PubMed
高影响因子
GREEN CHEMISTRY
·
2025
·
IF 9.2
Changhui Jing,Falin Li,Shuai Du,Xin Wang,Fengyuan Zhang,Songqi Ma
One-component epoxy resins have captured great attention due to their improved processing, environmental friendliness, quality stability, etc., but developing green and high-latent-efficiency ones is still urgent required. In this work, a bio-derived, high-latent-efficiency accelerator was facilely synthesized via Michael addition reaction of an abundant bioresource itaconic acid and imidazole. To confirm the latent mechanism, another accelerator without carboxyl group was synthesized from dimethyl itaconate and imidazole, and used together with imidazole as the controls. The chemical structures of the two synthesized accelerators were characterized in detail by FTIR, 1H NMR, 13C NMR and TOF-MS spectra. The latent and curing behavior of the one-component epoxy resins from bisphenol A epoxy, dicyandiamide and accelerators were studied by DSC and rheology, and the results showed that itaconic acid-modified imidazole systems possess long storage life at room temperature of above 210 days and can be cured rapidly at elevated temperatures. Otherwise, the imidazole system and dimethyl itaconate-modified imidazole system have short storage life below 1 day and 8 days, respectively. The excellent latent efficiency of itaconic acid-modified imidazole (IAIM) was attributed to the synergistical inhibit of the reactivity of imidazole toward epoxy groups through the steric-hindrance effect from the main structure of itaconic acid and the salt-formation effect from the carboxyl groups of itaconic acid. This work provides a green and simple strategy to synthesize high-efficiency latent curing accelerator.
研究领域:
材料科学
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化学工程
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF MEDICINAL CHEMISTRY
·
2025
·
IF 6.8
Tian Liu,Fengli Xia,Yi Zheng,Hongying Xiao,Yuanhao Yu,Jianbin Shi,Shuo Wang,Xianbao Shi,Zhonggui He,Jin Sun,Bingjun Sun
The rational design of tumor-responsive prodrug nanoassemblies requires precise control over systemic stability and site-specific activation. While α-position disulfide bonds are advantageous for rapid response to redox conditions, they also risk premature drug leakage during circulation. This study introduces a steric hindrance-guided approach to engineer disulfide-bridged podophyllotoxin homodimeric prodrugs for spatiotemporal controlled delivery. By monomethyl or dimethyl substitution of the carbon atoms adjacent to the α-disulfide bond, we can modulate steric hindrance. Excessive hindrance destabilizes the nanoassemblies and slows effective drug release, while moderate hindrance (monomethyl modification) enhances pharmacokinetic properties and promotes selective tumor activation. In vivo studies indicate that monomethyl-modified prodrug nanoassemblies exhibit superior antitumor efficacy and reduced off-target toxicity compared to PPT solution. This work underscores the importance of steric hindrance in optimizing prodrug nanoassembly stability and tumor-specific activation, offering a comprehensive strategy for redox-responsive nanomedicines.
研究领域:
药剂学
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肿瘤学
·
纳米医学
✓ 已验证
产品关联
DOI
PubMed
高影响因子
iScience
·
2023
·
IF 5.8
Xuan Ding,Jiayi Liu,Hui Shi,Zhou Yi,Lei Zhou,Wei Ren,Penghui Shao,Liming Yang,Derun Zhao,Yun Wei,Xubiao Luo
Efficient and selective removal of Pb(II) from wastewater with complex matrix remains a challenging task. Porous aromatic frameworks (PAFs) with predesigned functional building blocks provide a favorable platform for the selective separation of Pb(II). Herein, the bifunctional SPAFs with the introduction of -OH and -SO 3 H were synthesized through rationally optimizing their steric hindrance. As a result, the SPAF-0.75 exhibits favorable adsorption capacity of Pb(II) (212.34 mg g −1 ), which is 22 times larger than pristine framework. Competition experiment indicates that SPAF-0.75 possess the selective removal of Pb(II) without interfering from co-existing metal ions. The removal rate of SPAF-0.75 still retain at 100% after six successive cycles. The DFT calculation illustrates that -OH and -SO 3 H are co-participate in the process of capturing Pb(II), revealing SPAF-0.75 preferred removal of Pb(II) owing to the lowest adsorption energy (Δ E ab = −3.99 eV). This study extend the understanding of the structure-property relationship and facilitate new possibilities for PAFs.
研究领域:
材料科学
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环境科学
✓ 已验证
DOI
高影响因子
POLYMER
·
2019
·
IF 3.771
Yuan Qiu,Hongchao Yan,Jing Wang,Qian Jiang,Hong Wang,Haiyan Peng,Yonggui Liao,Xiaolin Xie,Bogumił E. Brycki
Constructing and regulating the helical structures of artificial foldamers have been constantly pursued because of their wide applications in chiral recognition, asymmetric catalysis , circularly polarized luminescence , etc. On the one hand, stabilizing the helical structures of foldamers can usually enhance the chirality by decreasing the pitches. On the other hand, the extended helix can be obtained when the π-π stacking interaction in the main chain is weakened. In general, the former aspect is inconsistent with the later. Herein, chiral 1-phenylethylamines, 2-phenylglycinols and leucinols are used as the guests to modulate the folded helix of an artificial poly(phenylenediethynylene)-based foldamer . With the aid of chiral center, the steric hindrance of the chiral guests can increase the distances between the pitches. Meanwhile, a more ordered chain arrangement is induced by such steric effect . As a result, we successfully endow the foldamers with an extended helix and enhanced chirality at the same time.
研究领域:
化学
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材料科学
✓ 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）