最新刊期
卷 53 ， 期 5 ， 2022
- 摘要：The main component of raw natural rubber is cis-1,4-polyisoprene (PI). To obtain better mechanical properties, raw natural rubber is usually vulcanized with sulfur to form a crosslinked network. To understand the relationship between the complicated network and the mechanical properties of vulcanized natural rubber (NR), several statistical models have been proposed since the 1940s by the pioneers such as Flory. To make complicated problems simple, two major assumptions were adopted in the models. (1) Only PI chains are considered in the crosslinked network. However, polysulfide chains are not included in the models. (2) Only the entropic elasticity of the network chains is taken into account, but the enthalpic elasticity (arising from variation of bond lengths and angles at large deformation) is ignored. As a result, there are several limitations in the traditional models. First, the traditional models fail to predict the elasticity of NR under large deformation. Second, the effects of sulfur content cannot be explained satisfyingly. To solve the above problems, Shuxun Cui and coworkers have made two modifications to the traditional models. First, the sulfur content is considered in the model. Second, the single-chain elasticities (which include both entropic and enthalpic elasticities) of the two main components of NR (PI and polysulfide) are integrated into the model. They found that the new model (called TCQMG model) is clearly superior to the traditional models (e.g., Gaussian model) in describing the mechanical properties of NR, especially for large deformation. In addition, the effect of sulfur content on the mechanical properties of NR can be explained well. Considering the similarity in network structures between NR and other vulcanized rubbers, it is expected that with more data of single-chain mechanics, this model may be used as a general model for various rubbers. With minor modifications, it is anticipated that the model could be applied in the field of supramolecular hydrogels.关键词：Vulcanized rubber;Elastic model;Single-chain elasticity;Progress
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发布时间：2024-10-08
Research Highlight
- 摘要：Drug delivery system is a system to deliver drugs to targets. An ideal delivery system can improve drug efficacy and reduce drug dosage, toxicity and side effects. This paper reviews the research progress of peptide-based drug delivery systems. Polypeptide (peptide) has the advantages of facile synthesis, easy metabolism, low immunogenicity, low toxicity and side effects. In addition, there are a large number of functional groups on the peptide branch chain, which can be coupled with drugs. Therefore, peptide-based drug delivery system has become an important development direction of drug delivery system, which is introduced from four aspects: targeting peptides, penetrating peptides, response peptides and assembling peptides with the examples and principles. Assembling peptides form nanostructures and enhance the stability of drug delivery system for long-term release. In vivo modulation of assembly behavior of peptides increased the intelligence and precise, showing great potential in clinical translation of drug delivery system.关键词：Targeting peptide;Penetrating peptide;Response peptide;Assembling peptide;Drug delivery system
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发布时间：2024-10-08 - 摘要：The most common safety problems of lithium-ion batteries mainly exist in electrolyte and diaphragm. Thermal runaway is the main cause of safety accidents of lithium-ion batteries. Changing electrolyte composition, increasing electrolyte composition, and introducing flame retardant additives can effectively alleviate and inhibit thermal effect and reduce flammability. Modification of polyolefin membrane is a simple method for improving the thermal stability of the membrane. The membrane is modified with high melting point polymer or inorganic materials. Its essence is similar to putting an "exoskeleton" on the membrane to resist thermal shock and mechanical shock. While ensuring the basic functions, the diaphragm should be more environmentally friendly and gradually turn to sustainable biomass materials. This review summarizes the safety protection measures of lithium-ion battery in recent years, mainly including the research and exploration results of internal and external protection measures in recent years. The action mechanism and research progress of nonflammable electrolyte, flame retardant additives, diaphragm, cathode materials, current limiting equipment, and battery management system reported recently are discussed in detail, and the development direction of lithium-ion battery safety research in the future is prospected.关键词：Lithium ion battery;safety;Separator;electrolyte;protective measures
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发布时间：2024-10-08
Review
- 摘要：Random incorporation of polar groups into polyolefins via coordination copolymerization has made a great progress in the past decades. In contrast, the preparation of polar functionalized conjugated diene rubbers receives less attention, although the polar groups play an important role in improving the mechanical properties of green tire. In this work, one kind of polar conjugated diene mononer IP-OTBS is prepared. Then, a series of rare-earth metal complexes 1‒5, which show different selectivities for isoprene polymerization, are utilized to initiate the homopolymerization of IP-OTBS in the presence of cocatalysts [Ph3C][B(C6F5)4] and AliBu3. Among them, complexes 1 and 2 still show high cis-1,4 selectivity (>98%) for IP-OTBS polymerization and, in contrast, the maximum value of 3,4 selectivity is 82.2% achieved by complex 3. Complexes 4 and 5, which show higher 3,4 selectivity (>98%) for isoprene polymerization, show moderate 3,4 selectivity (67.6%) and inert, respectively, under the same conditions. The copolymerizations of IP-OTBS with isoprene and butadiene using complex 2 generate the functional polybutadiene and polyisopene with cis-1,4 content of 10.2 mol% and 16.7 mol%, respectively. The bulky tert-butyldimethylsilane masked polybutadienes are readily transformed into the hydroxyl group functionalized polybutadienes or polyisoprene via the reaction with Bu4NF. Finally, we demonstrate that the polar group functionalized conjugated diene rubbers could be obtained via the stereoselective (co)polymerization of IP-OTBS by using rare-earth metal catalysts.关键词：hydroxyl-functionalized polybutadiene;Cis-1;4 selectivity;rare-earth metal catalysts;Butadiene;Isoprene
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发布时间：2024-10-08 - 摘要：The copolymerization of isopropylidene glyceryl glycidyl (IGG) and ethylene oxide (EO) with i-Bu3Al/H3PO4/DBU as catalyst has been examined. The microstructures, thermal properties and molecular weights of the obtained polymers were characterized by NMR, DSC and GPC. The copolymerization of IGG with EO has also been successfully achieved at room temperature in toluene. The EO-IGG copolymers with controllable contents were conveniently obtained in 100% yield within 30 min by changing the feed ratio of IGG to EO. The hydrolysis of EO-IGG copolymers afforded the corresponding hydroxyl functionalized copolymers (EO-GG) under acidic conditions for 2 h at room temperature, and the ketal structures in EO-IGG copolymers were completely transformed to hydroxyl. The 13C-NMR analysis of EO-GG copolymers showed that the hydroxyl groups were randomly distributed in EO-GG copolymers. The GPC analysis of EO-GG copolymers showed that the EO-GG copolymers with high molecular weight (Mn = 5.9×104‒18.1×104) and narrow distribution (Mw/Mn = 1.32‒1.54) were obtained. The molecular weight of the copolymers can be adjusted by changing the molar ratio of monomer to i-Bu3Al. The EO-GG copolymers with different compositions possessed a glass transition temperature (Tg = -5~-28 ℃), which increased with the hydroxyl content in EO-GG copolymers. When the EO content in EO-GG copolymers was higher than 90 mol%, the EO-GG copolymer possessed a melting point of 51 ℃. With the increase of the hydroxyl content in EO-GG copolymers, the hydrophilicity of EO-GG copolymers was improved obviously. By the two-step reaction of copolymerization and hydrolysis, the hydroxyl functionalized polyethylene oxides with high molecular weight were obtained in 100% yield, and the hydroxyl groups with controllable content were randomly distributed in the polyethylene oxide.关键词：Ethylene Oxide;Functionalization;Hydroxyl;Ring-opening polymerization
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发布时间：2024-10-08 - 摘要：In combination with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), the benzoxazolyl urea (NO) catalyst was very efficient for the solution ring-opening polymerization of L-lactide (L-LA) in the presence of benzyl alcohol. On the basis of homopolymerization, the solution ring-opening copolymerization of L-LA and δ-valerolactone (δ-VL) was investigated and the PLLA-co-PVL random and PLLA-b-PVL block copolymers were prepared via varying the feeding strategy (premixing or sequential feeding) and the feeding ratio of two monomers. The sequence structure of copolymers was analyzed by 1H- and 13C-NMR spectra and the copolymer compositions in the copolymers were in consistence with the feeding ratio of two monomers. The randomness R of the random copolymers prepared via premixing two monomers was about 0.5, which was between completely random and block copolymers. The thermal properties were tested by the differential calorimetry scanning (DSC). When the contents of two monomers in the copolymers were relatively close, no melting peak could be observed in the DSC curves and the samples was rubbery at room temperature as an amorphous polymer. As the content of VL segments decreased, the glass transition temperature of random copolymers increased. In addition, the block copolymers (PLLA-b-PVL) were synthesized through the "one-pot method" and "chain extension method". The sequence of segments was controllable and the randomness R approached zero.关键词：Benzoxazolyl urea;L-lactide;δ-Valerolactone;Copolymerization
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发布时间：2024-10-08 - 摘要：Producing biodegradable plastics from CO2 is a promising methodology for recycling industrial waste gas, and the conservation of environment and energy. Propylene oxide (PO) has been commonly used to copolymerize with CO2 to yield biodegradable poly(propylene carbonate) (PPC). PPC exhibits excellent transparency, low water and oxygen permeability as well as high flexibility. But low glass transition temperature (Tg) limited its practical applications. In recent years, the copolymerization of PO, CO2 with phthalic anhydride (PA) provides a robust and economical method to improve PPC's thermal and mechanical performance. In this study, to explore the relationship between the sequence structure and the properties of CO2/PO/PA terpolymer (PPC-P), PPC-P terpolymers with similar polyester (PE) content and molecular weight but different sequence structures (block, tapered and random) were synthesized through one-pot two-step method or one-pot one-step method using non-metallic catalytic system (TEB/PPNCl). The effects of polymerization temperature and reaction time on the composition and molecular weight of the PPC-P were systematically studied, and the PE content and molecular weight of all the terpolymers were controlled to be around 45% and 5.0×104, respectively for comparison. The typical sequence structure characteristics of the terpolymers were proven by 1H-NMR. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile test were used to characterize the thermal and mechanical properties of the PPC-P terpolymers. The block terpolymer shows two glass-transition temperature (Tg) (43 and 54 ℃), while the tapered and random terpolymer has only one Tg (51, 50 ℃). The Td5 of the block terpolymer (263 ℃) is lower than that of the tapered and random terpolymer (around 273 ℃), indicating the poorer thermostability of block terpolymer. The three terpolymers with different sequence structures have similar tensile strength (around 35 MPa), all belonging to hard and brittle materials.关键词：CO2 based copolymer;Sequence structure;Thermal properties;Mechanical properties
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发布时间：2024-10-08 - 摘要：A series of polyimide membranes containing polyether amine (PPO) segment were successfully synthsized by thermal imidization of the poly(amic acid) (PAA) precursors copolymerized of pyromellitic dianhydride (PMDA) with 4,4'-diaminodiphenyl ether (ODA) and amine functionalized polyether amine (Mn~2000). The effects of PPO on the microstructure and gas separation property of the resultant membranes were investigated in detail. The results show that the fractional free volume (FFV) of the membranes increases with the content of the PPO. Meanwhile, a micro-phase separation behavior is detected in the resultant membranes with the incorparation of PPO, which can act as the continuous gas transmission channel. As a consequence, the permeability of the membrane increases rapiadly. As the PPO content reaches 65 wt%, the CO2 permeability is as high as 131.61 Barrer, which is nearly 22 times higher than that of the PMDA/ODA homopolyimide membrane. Moreover, due to the special interaction between the PPO and CO2, the CO2/N2 selectivity increases from 18.77 for the PMDA/ODA membrane to 30.12 for the copolyimide membrane with 65 wt% PPO. Accordingly, the incorporation of PPO plays an important role in modifying the microstructure and gas separation property for the polyimide membranes.关键词：Polyimide;Polyether amine;Gas separation membrane;Micro-phase separation
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发布时间：2024-10-08 - 摘要：Polybutene-1 (PB-1) could behave different crystallization paths when it is finely dispersed into large number of small droplets, which is so-called "fractioned crystallization" phenomenon. According to our previous research, the nucleation of the kinetic favored form Ⅱ could be suppressed when it is blended with polypropylene (iPP) with content lower than 20%. In this situation, trigonal form I' could be generated at the interface of the droplets. Self-nucleation and the manipulation of isothermal crystallization temperature methods are involved to modify lamellar thickness of iPP in this work. These results clearly show that crystallization temperature of PB-1 trigonal crystals is controlled by Ts temperatures. According to Gibbs-Thomson equation, it could be concluded that the nucleation of form I' could be hindered by thicker iPP lamellae. In situ wide angle X-ray diffraction (WAXD) experiment is also conducted, which confirms that the melt and re-crystallization of PB-1 is controlled by the existence of form Ⅱ nuclei generated at low temperature. Pure form I' could melt directly without transforming into form Ⅱ crystals during heating process. Our results shed new lights on understanding the effect of interface on fractionated crystallization.关键词：Polypropylene;Polybutene-1;Confined space;Crystallization
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发布时间：2024-10-08
Research Article
- 摘要：Two-dimensional correlation spectroscopy (2Dcos) is an advanced analysis method, which holds great advantages in improving spectral resolutions and interpreting dynamic processes, and has attracted great attention in the field of polymers. Molecular spectroscopy is frequently applied in the characterization of polymers, which involves abundant molecular interactions and complex structures. Under the help of 2Dcos analysis, fine structures as well as dynamic mechanisms within the polymer systems can be effectively identified, thus significantly enriching and improving the analysis results. In this paper, we will mainly focus on the two-dimensional correlation infrared spectroscopy (2DIR). Firstly, the history and basic principles of 2Dcos are briefly introduced. Then, some relevant experimental and analytical techniques are presented based on the actual process. Finally, typical applications of 2DIR in the polymer characterization are demonstrated and the features thereinto are also shown. Particularly, the response mechanisms of temperature-responsive polymers, complex molecular interactions in stretchable ionic conductors, diffusion processes of small molecules in polymer matrix and structures of natural polymers are investigated. It is hoped that this paper will help readers better understand 2Dcos and further expand its applications in the field of polymers.关键词：Molecular spectroscopy;Two-dimensional correlation spectroscopy;Polymer;Molecular interactions
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发布时间：2024-10-08 - 摘要：Scanning electron microscopy (SEM) is one of the most important tools for the characterization of polymer materials' microstructure and composition. First, it is easy to operate; then there are various electronic signals available which contain different sample information for SEM imaging; besides, there are little sample damage during SEM observation. In this work, the working principle of SEM was elucidated systematically. Also, a comparison was made between SEM and TEM with respect to working principle, resolution and magnification, view and depth of field, sample preparation, sample damage and pollution. Therefore, the advantages and features of SEM were highlighted. In addition, the experiment methods of SEM were illustrated in detail, including sample preparation, instrument parameter settings, operation skills and image treatment. The key factors which determines the quality of SEM image were revealed. The main applications of SEM in polymer characterization were introduced. Specifically, the secondary electrons imaging was used to investigate the microstructure of polymer composition, compatibility of polymer blends, crystal structure of polymer, morphology of polymer porous membrane, biocompatibility of polymer material, self-assemble behavior of polymer and so on. Besides, the backscattered electrons, characteristic X-ray, transmittance electrons were also used to reveal the morphology and composition information of polymer systems. The combination of SEM with Raman spectrometer and Focused ion beam and the in situ SEM techniques were illustrated. Finally, the recent trends of SEM development were prospected.关键词：Scanning electron microscopy;polymer material;Microstructure;Composition;Application
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发布时间：2024-10-08
Review (Special Topic: Techniques of Polymer Characterization)
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