最新刊期
卷 52 ， 期 7 ， 2021
- 摘要：Porous carbon materials exhibit high porosity, good electronical conductivity, excellent structural stability and tunable physicochemical properties, and thus find use in a series of areas, including energy storage and conversion, adsorption and separation, catalysis, petrochemical industry, and biological medicine. The physicochemical structures of their precursors are critical to the pores and skeletons of porous carbon materials, thus significantly affecting their properties in various applications. Polymers with controllable physicochemical structures, good carbonizability and desirable morphology inheritability have been regarded as promising precursors for preparation of high-performance porous carbon materials. Recent years have witnessed continuous research breakthroughs in the customization of a series of novel porous carbon materials with various structures and functionalities, based on the precise design of polymer structures, innovation of synthesis methods, and optimization of carbonization technology. Herein, according to the recent research progresses in our group and others groups in domestic and foreign countries, this feature article summarizes the theories of direct-carbonization and templating methods for polymer-derived porous carbon materials, discusses the functionalization strategies of their carbon skeletons, and illuminates the effects of chemical structure and microcosmic morphology of polymers on pores and skeletons of porous carbon materials. Finally, an outlook is prospected with regard to the concerns and challenges for the future study on polymer-based porous carbon materials.关键词：Polymers;Porous carbon materials;Structural design;Controllable preparation;Functionalization
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发布时间：2024-02-20 - 摘要：Optical imaging plays an important role in the biomedical field due to its noninvasiveness, high spatiotemporal resolution, and high sensitivity capabilities, which allows for real-time visualization of numerous cellular and molecular processes in living organisms to investigate their biological functions. As one of the most widely used optical imaging techniques, fluorescence imaging suffers the relatively poor signal-to-background ratio (SBR) and low tissue penetration depth due to light scattering and tissue autofluorescence induced by real-time light excitation. To address these issues, self-luminescence and photoacoustic (PA) imaging have recently developed, which eliminate concurrent light excitation and detect acoustic signals with minimized acoustic scattering, respectively, leading to higher SBR and deeper imaging depth relative to fluorescence imaging. This review focuses on the recent development of semiconducting polymer nanoparticles (SPNs) for self-luminescence and PA imaging. The molecular engineering design approaches to amplifying the self-luminescence efficiency and PA brightness of SPNs are highlighted. The design strategies based on the chemically initiated electron exchange luminescence (CIEEL) to amplify the chemiluminescence intensity of SPNs and the afterglow luminescence imaging of phenylenevinylene-based SPNs are introduced. The design strategies including the fluorescence quenching or accelerated heat dissipation to amplify the PA brightness of SPNs are also introduced. Then, the SPN-based smart activatable probes for in vivo PA imaging are discussed. The facile modification and intraparticle engineering allow SPNs responsive to various biological and pathological indexes, including pH and reactive oxygen species (ROS), and the designs and PA imaging applications of these SPN-based activatable probes are introduced in detail. Finally, current challenges and perspectives of SPNs in the biomedical field are proposed.关键词：Optical imaging;Self-luminescence imaging;Photoacoustic imaging;Semiconducting polymer nanoparticles;Biomedical applications
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发布时间：2024-02-20
Feature Article
- 摘要：The ring-opening polymerizations of N-substituted glycine N-thiocarboxyanhydrides (NNTAs) initiated by 1,8-diazabicycloundec-7-ene (DBU) were investigated. Homo- and co-polymerizations of N-ethylglycine N-thiocarboxyanhydride (NEG-NTA) and N-butylglycine N-thiocarboxyanhydride (NBG-NTA) initiated by DBU were carried out in THF at 60 ℃, which produced corresponding poly(N-ethylglycine) (PNEG), poly(N-butylglycine) (PNBG) and poly(N-ethylglycine-co-N-butylglycine) (P(NEG-co-NBG)) with high yield (>86%) and narrow dispersities (1.13-1.25). By adjusting monomer to initiator feed molar ratios ranging from 10 to 100, the molecular weights of PNEGs could be tuned from 900 g/mol to 7500 g/mol, which showed the good controllability of the polymerizations. 1H-NMR and MALDI-ToF mass analyses revealed the structures of cyclic polypeptoids bearing one DBU moiety and one thiocarbamate group. The DBU moiety would be eliminated by potassium trifluoroacetate during the MALDI-ToF analysis and DBU-free cyclic polypeptoids were formed. The existence of thiocarbamate group was further proven by 13C-NMR and FTIR analyses. To further confirm the cyclic structures of the products obtained by using DBU initiator, linear polypeptoids were synthesized as comparisons by benzylamine (BA)-initiated NNTA polymerizations. With the same degree of polymerizations (DPs), polypeptoids obtained by DBU initiator had lower hydrodynamic volumes, which indicated their cyclic structures. The living characteristics of DBU-initiated NNTA polymerizations were finally supported by the chain extension reaction. The polymer chain could continue propagating after the addition of another batch of monomers, and the molecular weight of the product increased significantly while the dispersity kept narrow (Đ=1.23). DBU-initiated NNTA polymerizations went through zwitterionic ring-opening polymerization mechanism. Attack of DBU on NNTA would generate a zwitterionic propagating intermediate, in which DBU cation and thiocarbamate anion interacted strongly with each another by electrostatic interaction. The chain propagation caused by NNTA monomer addition at the thiocarbamate end of zwitterionic propagating intermediate. And then, end-to-end macrocyclization between DBU cation and thiocarbamate anion formed cyclic polypeptoids. Since NNTAs are more stable monomers compared to NNCAs, and DBU is an accessible initiator, DBU-initiated NNTA zwitterionic ring-opening polymerization is a simple and facile method for the synthesis of cyclic polypeptoids.关键词：Polypeptoids;Zwitterionic ring-opening polymerization;Cyclic polymers;N-Thiocarboxyanhydrides;Organic bases
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发布时间：2024-02-20 - 摘要：Poly(ester amide)s (PEAs) are important synthetic polymeric materials. The excellent biodegradability and mechanical properties make the synthesis of such kinds polymers a research hotspot in the field of polymer chemistry. Herein, we report a novel strategy for accessing PEAs via the alternating copolymerization of easily synthesized aziridine derivatives and cyclic anhydrides with binary catalytic system consisting of benzyl alcohol (BnOH) and organic base (7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD)) as catalyst, followed by the deprotection for the substitutes on the N atoms groups of the resultant copolymers using K2S2O8/Na2HPO4 system. A detailed study on the debenzylation reaction was carried out. It was found that the K2S2O8/Na2HPO4 system can effectively realize the debenzylation reaction involving the copolymer from 2,4-dimethoxy-N-benzylaziridine. The nine kinds of PEAs with different structures were synthesized from two types of monomers. The metal-free strategy, give these PEAs the potential to be utilized as hydrogels, tissue engineering, elastomers and smart materials as well as high-performance engineering plastics. Studies focused on further expanding the monomer scope and controlling the stereochemistry are currently in progress.关键词：Poly(ester amide)s;Debenzylation;Metal-free catalysis;Alternating copolymerization
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发布时间：2024-02-20 - 摘要：A series of temperature-responsive chiral amphiphilic random copolymers poly(NIPAAm-co-chiral salen TiIV, PNxSy) were prepared by using N-isopropylacrylamide and 5-vinyl chiral salen TiIV as the monomers, azodiisobutyronitrile as the chain initiator, and benzyl dithiopropionate as the chain transfer agent. The successful copolymerization of the chiral salen TiIV moiety with NIPAAm was illustrated by FTIR. The water-solubility switching process and LCST were characterized by monitoring the optical transmittance of PNxSy solution at 450 nm using UV-Vis spectrophotometry. Dynamic light scattering (DLS) was used to further prove the influence of the ratio of hydrophilicity to hydrophobicity on the hydration kinetic particle size of amphiphilic random copolymers. Transmission electron microscopy (TEM) and circular dichroism (CD) spectroscopy were used to reveal the effect of temperature on the chirality of amphiphilic random copolymers. This kind of thermo-responsive chiral amphiphilic random copolymers can realize efficient asymmetric catalytic reaction in pure water phase. Only 0.1 mol% of PN120S8 was sufficient to exhibit extremely high activity (conversion >95%) with up to 97% chemoselectivity and enantioselectivity (>98%) for a wide range of sulfides in water. After reaction, the PNxSy became hydrophobic upon heating above its LCST, and precipitated from aqueous system for recovery. It can be recycled and reused for seven times without significant loss of the activity.关键词：Temperature-responsive;Chiral copolymers;Pure water phase;Asymmetric reaction;Recycle and reuse
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发布时间：2024-02-20 - 摘要：The long alkyl chain and carbon-carbon double bonds were introduced on the surface of starch through the reaction of starch and acid chloride, which endowed the starch with excellent emulsification properties and reaction sites. Then the core-shell starch-based nanoparticles, where the starch worked as the rigid core while poly(ethyl acrylate) (PEA) served as the soft shell, were prepared by soap-free emulsion copolymerization of ethyl acrylate (EA) to form PEA shell covering the starch. After that, glycidyl methacrylate (GMA) was added into the core-shell nanoparticles emulsion to prepare epoxy functionalized core-shell nanoparticles. Finally, the obtained epoxy functionalized core-shell nanoparticles were melt-blended with poly(lactic acid) (PLA) and PLA-based nanocomposites were prepared. Effects of epoxy functionalized core-shell nanoparticles on the mechanical properties of PLA were studied. FTIR spectra and TEM test revealed that the epoxy functionalized core-shell nanoparticles with an average particle size of around 250 nm were successfully prepared. Mechanical property test showed that the prepared epoxy functionalized core-shell nanoparticles dramatically improved the toughness of PLA and maintained its high tensile strength. Specifically, the notched impact strength of the blends was as high as 17 times that of neat PLA. In addition, the SEM and DMA tests indicated that the introduction of epoxy functional groups of core-shell nanoparticles significantly improved the compatibility of core-shell nanoparticles with PLA matrix.关键词：Esterified starch;Core-shell particles;Epoxy functionalized;Poly(lactic acid);Toughening
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发布时间：2024-02-20 - 摘要：Herein, a nitrogen-doped carbon dots (N-CDs)/alginate nanocomposite was prepared by a simple and convenient microwave method. In this method, alginate served as the carbon source and ethylenediamine served as the nitrogen dopant. Transmission electron microscopy (TEM) observation shows that there exist nanoparticles in the N-CDs/alginate nanocomposite with the average size of 4.6 nm. The fluorescence properties of the N-CDs/alginate nanocomposite were analyzed using fluorescence spectroscopy and ultraviolet-visible (UV-Vis) absorption spectroscopy. The UV-Vis spectrum of the N-CDs/alginate nanocomposite shows a broad absorption peak from 300 nm to 350 nm, which is attributed to N-CDs in the nanocomposite. The photoluminescence spectrum of the N-CDs/alginate nanocomposite shows a typical excitation-dependent photoluminescence feature. Moreover, the N-CDs/alginate nanocomposite presents a clear blue fluorescence under 365 nm UV light. The nanocomposite retains the property of alginate to bind Ca2+ to induce the gelation of alginate, which can be used to perform the anodic electrodeposition of the N-CDs/alginate nanocomposite. On the other hand, it also retains the coordinated capability of alginate to interact with metal ions (such as Zn2+) to form a gel, which can be employed to carry out the coordination electrodeposition of the N-CDs/alginate nanocomposite. By taking advantage of the spatial selectivity of electrodeposition technique, the deposited N-CDs/alginate nanocomposite films with specific shapes and fluorescence patterns can be conveniently fabricated on electrodes. The thickness of the electrodeposited N-CDs/alginate film increases with the increase of electrodeposition time, which provides a controllable means to produce the electrodeposited N-CDs/alginate film with different thicknesses. Furthermore, the electrodeposition of the N-CDs/alginate nanocomposite enables a facile way to generate CDs nanocomposite film modified electrodes to conduct electrochemical detection. Thus, the N-CDs/alginate nanocomposite prepared by the microwave method has potential applications in fluorescence imaging and electrochemical detection.关键词：Electrodeposition technique;Carbon dots;Alginate;Microwave method;Biopolymer
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发布时间：2024-02-20 - 摘要：The structure parameters of 78 polyimides with different chemical structures were collected by using quantum chemistry method and group contribution method. Eight structural parameters with significant influence on dielectric constant were selected from 16 kinds of parameters by path analysis. On this basis, two kinds of quantitative structure-property relationship models for polyimide were constructed, and the average relative errors were within 10%. It is considered that the most important factor affecting the permittivity of polyimide film is molecular volume, which is the free volume size of the molecular from the macroscopic point of view. The applicability and stability of the two models are evaluated. It is found that artificial neural network has higher accuracy, the relative error is less than 5%, and the accuracy of multiple linear regression model is less than 10%, but it has better physical significance. Eighteen polyimide structural units with low dielectric constant were designed and their dielectric constants were predicted. It is shown that the dielectric constant can be reduced by increasing the fluorine content of the molecular, and the optimum fluorine content is between 0.25 and 0.37. The optimal ratio of side chain to main chain is about 0.5-0.6, which will lead to the increase of dielectric constant. Based on the above research, three polyimide structures with ultra-low dielectric constant were designed, and the lowest predicted dielectric constant was 1.22.关键词：Polyimide;Dielectric constant;Quantitative structure-property relationship;Multiple linear regression;Artificial neural network
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发布时间：2024-02-20 - 摘要：Accelerated aging tests were employed to study the aging behaviors of nitrile rubber under the coupling conditions of temperature, oil medium and compression. Physical properties and chemical structures of the aged samples were evaluated by the changes of compression set, functional groups, thermal stability, crosslinking density, glass transition temperature and microscopic morphologies, etc. During the aging process, the volatilization of plasticizer, post-crosslinking, oil diffusion and hydrolysis of cyano groups partially on the surface of the samples could simultaneously occur. Attenuated total reflection-fourier transform infrared (ATR-FTIR) results indicated that under the air condition, the volatilization of plasticizer is dominated at higher temperature. However, under oil medium condition, the presence of oil could inhibit the volatilization of residual moisture on the surface of the samples, and then hydrolysis reaction of the cyano groups occurred, which could be further promoted by the tensile stress on the lateral surface of the sample induced by compression. Thermogravimetric analysis (TGA) results suggested that there is a competition between plasticizer volatilization and oil diffusion under oil medium condition, which is different from the situation under air condition. The results of compression set, crosslinking density and glass transition temperature showed that the oil medium could significantly inhibit the post-crosslinking of the rubber compared with that aged in air, while compression may promote it. The aging under all test conditions was dominated by post-crosslinking and no obvious chain scission or degradation was observed.关键词：Nitrile rubber;Accelerated aging;Oil medium;Compression;Crosslinking density
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发布时间：2024-02-20 - 摘要：Wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and small-angle laser light scattering (SALS) were used to systematically characterize the multi-level condensed matter structure of linear low-density polyethylene (LLDPE) cast films and LLDPE cast films with the nucleating agent HPN-20E. The relationship between the barrier properties and the condensed matter structure of the cast film is studied. It is pointed out that when the crystallinity is similar, the orientation of the crystal is the key factor affecting the barrier, and a quantitative orientation structure parameter RND is proposed, which is the ratio of the diffraction peak area of (110) crystal plane to the (200) crystal plane when X-ray incident along the ND direction. The relationship between crystal orientation and barrier property is confirmed. The main orientation of PE crystals in the cast film without nucleating agent is the spiral-oriented crystal with b-axis as the helical axis, where b axes are in the TD-ND plane. The PE crystals in the cast film are rarely oriented with the b-axis along the MD direction. The addition of nucleating agent changes the distribution and orientation of the crystals in the cast film. Among the three typical orientations in PE films, the spirally oriented crystals with the b-axis along the ND direction (OND) possess the worst barrier performance. Therefore, when the crystallinity is similar, the lower the OND content, the better the barrier performance of the sample. A larger RND value indicates a lower OND content with a similar crystallinity. The RND values of the two PE samples are significantly increased after adding the nucleating agent HPN-20E, indicating that the OND content is significantly reduced, so the barrier performance is improved. The RND value of sample 7050 increased more with the addition of nucleating agent, so its barrier performance is improved to a greater degree. Moreover, the addition of nucleating agent also changes the size and orientation of the lamellae, and the microscopic aggregation of the crystal. The results showed that crystal orientation is a key factor affecting barrier performance.关键词：Polyethylene;Barrier properties;Crystallization;Orientation
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发布时间：2024-02-20 - 摘要：In order to improve the calculation accuracy of the numerical simulation of rubber dynamic heat build-up, based on the time-temperature equivalence principle, a new method to determine the tensile test conditions taking into account both temperature and strain rate is proposed in this study. It may meet the test conditions of equipment and service conditions of rubber products at the same time. Moreover, in order to obtain more accurate parameters of the hyperelastic constitutive equation, a set of stresses obtained by stress relaxation experiment under the fully relaxed state of rubber is used to fit the hyperelastic model of viscoelastic approach. Based on the mentioned test methods and ABAQUS software, the dynamic compression heat generation finite element models of rubber cylinder are established. Considering the influence of temperature, strain rate and dynamic strain amplitude on the mechanical properties of rubber, the heat build-up calculation method based on loss tangent and hyperelastic model and viscoelastic heat build-up calculation method based on Prony series in frequency domain are respectively used to calculate the compression heat build-up of rubber cylinder. The results show that the temperature rise calculated by the two approaches are in agreement with the experimental results of compression heat build-up, but the viscoelasticity algorithm has higher accuracy, and the heat build-up history predicted agrees well with the experimental results, which can better describe the hysteresis heat build-up phenomenon of rubber, consequently verifying the correctness of the material test conditions proposed in this study.关键词：Rubber dynamic heat build-up;Time-temperature equivalence principle;Numerical simulation;Viscoelastic model
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发布时间：2024-02-20 - 摘要：In this study, creep dynamics of associative polymers is analyzed on a basis of Rouse model. The association sites, i.e., the stickers, are introduced via increasing the segmental friction of the associative sites. First, we clarify the relationship between the Rouse model with frictional distribution and the sticky-Rouse model with stickers having fixed “lifetime”. Namely, we explain how to choose the friction coefficient so as to model the associative polymers with stickers of fixed lifetime. Comparison between the prediction of the Rouse model with frictional distribution and either the discrete or the continuous sticky-Rouse model rationalizes the choice. Second, we use the Rouse model with frictional distribution to analyze the conformational evolution of non-entangled symmetric associative polymers during the start-up shear and creep processes. During the start-up shear, the orientation function (representing an average segmental orientation of a given position of the chains) increases with time, and finally reaches the steady state. The orientation function increases from the ends to the center of the chains, akin to that of non-associative polymer chains. Nevertheless, we find a unique stepwise increase of orientation anisotropy at the sticky sites. We attribute this feature to the dynamic roles of the sticky and non-sticky segments. Namely, the sticky segments are strongly oriented by the shear flow field, and the non-sticky segments confined between the sticky segments are forced to transmit the orientational force of the sticky segments. During the creep process with fixed stress, the evolution of the conformation function experiences obviously two stages. In the early stage, only the segmental motion is activated, where the sticky and non-sticky segments behave accordingly to their intrinsic nature, i.e., the sticky and non-sticky segments increase and decrease the orientation function, respectively, so as to maintain the steady stress. In the second stage, the segmental motion extends gradually to the chain dimension and the orientation function of both the sticky and non-sticky segments achieve gradually to the steady-state.关键词：sticky-Rouse model;Frictional distribution;Start-up shear;Creep
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发布时间：2024-02-20
Research Article
- 摘要：In this review, the authors introduce the brief history, basic principles, sample preparation, and applications of quartz crystal microbalance (QCM). With the development of QCM technique, the quartz crystal microbalance with dissipation (QCM-D) has been employed to carry out the studies in a wide range of fields of polymer films because it can simultaneously obtain the information on the changes in mass and stiffness of polymer films. Moreover, the combined QCM-D and spectroscopic ellipsometry (QCM-D/SE) technique can be used to further obtain the thickness change and other information of polymer films. To demonstrate the applications of QCM-D in polymer studies, this review presents how the QCM-D and QCM-D/SE can be used to study the conformational behaviors of polymers grafted at interfaces, the ionic effects on polymers, and the polymeric marine antifouling materials. Specifically, (i) QCM-D can be used to study both the conformational behaviors of grafted polymers during the pancake-to-brush and mushroom-to-brush transitions and the stimuli-responsive behaviors of grafted polymers with temperature, pH, and salt concentration as the external stimuli; (ii) QCM-D/SE can be applied to study the ionic effects on polyelectrolyte brushes including specific ion effects, ionic hydrogen bond effects, and ionic hydrophilicity/hydrophobicity effects. The relevant studies can not only clarify the mechanisms of the ionic effects on polyelectrolyte brushes, but also demonstrate that the properties of polyelectrolyte brushes can be tuned with these ionic effects; (iii) QCM-D can be employed to evaluate the performance of polymeric marine antifouling materials, providing a method to screen the materials in laboratory, saving much time and money for marine field tests. The authors hope that this review can provide an inspiration on how to apply QCM-D to carry out polymer studies, enabling this technique to solve more problems in the field of polymers.关键词：Quartz crystal microbalance;Polymer brushes;Polyelectrolytes;Ionic effects;Marine antifouling materials
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发布时间：2024-02-20 - 摘要：Small-angle X-ray scattering (SAXS) technique is one of the most significant methods for determining the micro-structures of polymeric materials due to its statistical average and nondestructive detecting feature. Usually, a monochromatic parallel beam of X-rays is used for scattering experiments. When passing through a sample, the oscillating electromagnetic field (mostly the electric part) of X-rays interact with electrons, making the electrons secondary sources of X-rays of the same frequency. Those secondary X-rays interfere with each other to form a specific pattern deviating from the primary beam path depending on the actual locations of the electrons in the sample. Mathematically, such interferences can be obtained by a summation of all secondary X-ray waves. As the number of the electrons within the sample is very large, an integration is used to represent the summation mentioned above. Because of the wave nature of the X-rays, the amplitude of the scattered X-rays determined by the above integration is just a Fourier transformation of the electron density distribution within the scattering volume. Due to the limitation in detection technique, the complex value of amplitude of scattered X-rays with real and imaginary parts cannot be recorded. It is the intensity rather than the amplitude that is recorded during experiments resulting in a loss of the phase information. Therefore, obtaining exact structural information (electron density distribution) becomes not easy and must be based on specific model fittings. Besides structures, SAXS intensity distribution can be used to investigate sample’s gross properties such as fraction of phases or local properties such as fractal dimensions of interfaces between phases. This work began with an introduction of the fundamental theories of the SAXS technique, followed by practical suggestions on performing the experiments and brief summaries of models developed for different structures. The authors wish this review could help the beginners to comprehend the elements of the SAXS technique and serve as an instruction manual for valid data acquisition.关键词：Polymer characterization;Small-angle X-ray scattering (SAXS);Lamellae;Micro-structure
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发布时间：2024-02-20 - 摘要：Nuclear magnetic resonance (NMR) techniques based on the nuclear spins can provide important information on microscopic structure and dynamics in a very broad length and time scale. With the booming development of NMR theory and instruments, solid-state NMR (SSNMR) is playing an increasingly important role in the field of polymer material researches. SSNMR has gradually become a powerful tool for the characterization of structure and dynamics of macromolecules, changes of chemical bonds, interactions between polymer chains, relationships between the microstructure and macroscopic chemical/physical properties, which almost covers all areas of polymer researches and is suitable for different polymer systems including polymer solutions, melts, gels, liquid crystals, crystalline and amorphous solids, etc. SSNMR not only plays an important role in elucidating the relationship between structure and properties for polymer materials, but also is of great significance for developing the theory of polymeric condensed physics, which has given a significant impulse to the development of polymer science. In this paper, the basic principles, experimental methods and skills, typical applications and progresses in polymer science are briefly reviewed. In the section of basic principles, the nuclear spin interactions and its experimental manipulation methods for detecting information on different length scales, such as chemical shift anisotropy and dipolar interactions, high-resolution SSNMR techniques such as magic-angle spinning, cross-polarization and multiple pulse decoupling, as well as the principles of spin diffusion method for measuring microdomain and interphase structures, and complex molecular motion on different time scale, are introduced. In the section of experimental methods and skills, we pay great attention to accurate calibration of the SSNMR instrument, key setting of the pulse parameter and background signal suppression of the instrument. In the section of typical applications and progresses, we focus on different topics including the structure property relationship of natural polymers and their composites, the interaction between water and biological macromolecules, the structure of microphase separation in multiphase polymer materials, the interaction of hydrogen bonds in polymers, as well as conductive polymer materials. The latest applications and progress of solid-state NMR technology in the aforementioned fields are also introduced.关键词：Solid-state NMR;Polymers;Microstructure;Dynamics;Structure and property
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发布时间：2024-02-20
Review
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