最新刊期
卷 51 ， 期 10 ， 2020
- 摘要：Epoxide represents a major family of raw materials and monomers for heterochain polymers that have shown great utilities in academia, industry, and everyday lives. Typically, mega tons of ethylene oxide and propylene oxide are consumed annually, producing polyethers in the forms of homopolymers, statistical copolymers, block copolymers, etc. Therefore, ring-opening (co)polymerization (ROP/ROCP) of epoxides and copolymerization of epoxides with non-epoxide (heterogenous) monomers have long been one critical topic in synthetic polymer chemistry. Since the beginning of 21st century, organocatalytic/metal-free polymerization has been a fast growing area of research, which has vigorously spurred on the long-established field of epoxide (co)polymerization. Strong organobases including phosphazene bases, N-heterocyclic carbenes, and N-heterocyclic olefins constituted the first group of organocatalyst used to promote alcohol-initiated (oxy)anionic ROP of epoxides. In addition to controlling the molar mass and end-group functionality of polyethers, such endeavors also led to a series of new strategies, such as “catalyst switch”, for facile construction of epoxide-based heterogeneous copolymer structures. Mild non-nucleophilic organobases next stood out, showing good selectivity and control for epoxide-based alternating ROCP, due to a self-buffering mechanism based on proton shuttling between chain end and catalyst. The simple organobase also exhibited the capability in one-step synthesis of block copolyesters by sequence-selective terpolymerization of epoxide, cyclic anhydride, and cyclic ester that had been a filed long dominated by metallic catalysts. It was of great interests that some side reactions associated with organobases, such as macromolecular transesterification and oxygen-sulfur exchange, could be ingeniously utilized to develop new polymerization reactions and polymer synthesis methods. In very recent years, acid-base type two-component catalytic systems comprising a relatively mild organobase and a organoboron compound or aN,N-disubstituted (thio)urea have been prevailing because of the distinctly enhanced catalytic efficiency and chemoselectivity. In particular, organobase-triethylborane catalytic system showed strict selectivity for epoxide ROP over transesterification, which was attributed to a double-alkylborane-coordinated activated chain end mechanism. Therefore, a few long-standing challenges were well addressed, such as sequence-reversible block copolymerization of epoxide and cyclic ester, one-step synthesis of polyether monoester using carboxy initiators, etc. The above-mentioned achievements and insights, among others, will be summarized.关键词：Epoxide;Ring-opening polymerization;Copolymerization;Organocatalytic polymerization;Metal-free polymerization
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发布时间：2021-01-26 - 摘要：Poly(amino acid)s are important biomimetic materials due to their unique biocompatibility, and potential application in gene transfection, drug delivery, and prevention of viral infections. For example, poly(ε-lysine) is an uncommon cationic homopolymer produced by the fermentation process. Although poly(amino acid)s are developing rapidly, the simple synthesis of poly(amino acid)s, especially functional poly(amino acid)s such as poly(ε-lysine) still remains a challenge. Fortunately, we have seen a drastic rising trend in the area of organocatalytic ring-opening polymerization (ROP) of amino acid-based monomers for polymers. Our lab succeeded in developing a superbase t-BuP4-catalyzed ROP of cyclic lysine monomers, affording high molecular weight poly(ε-lysine) bearing pendant protected amino groups with high monomer conversion (up to 95%). The organocatalytic polymerization could proceed at low reaction temperature (e.g., 60 °C) compatible with readily removable protecting groups, providing a sustainable and new methodology toward facile preparation of poly(ε-lysine). Moreover, we developed an effective bifunctional single molecule organocatalysis for selective ROP of amino acid-based O-carboxyanhydride (OCA) monomers without epimerization. The close vicinity of both activating groups in the same molecule engender an amplified synergetic effect and thus allows for the use of mild bases, thereby leading to minimal epimerization for polymerization. In the following article, recent examples of the organocatalysis for amino acid-based polymers synthesis are presented, as will their suitability for stereoregular isotactic polymers. The advantages and limitations of the organocatalytic ROP of amino acid-based monomers are discussed, which is important for the simple and general synthesis of amino acid-based polymers.关键词：Organocatalysis;Amino acid;Poly(ε-lysine);Ring-opening polymerization;Stereoregularity
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发布时间：2021-01-26 - 摘要：The harmlessness and high-value utilization of one-carbon (C1) building blocks are the frontier issues in synthetic polymer chemistry. The copolymerization of carbonyl sulfide (COS) or carbon disulfide (CS2) with epoxides is a promising method of synthesizing sulfur-containing polymers. In recent years, organocatalysts have been successfully developed to catalyze the polymerization process of COS(CS2) owing to their low toxicity, insensitivity to air and water, and good substrate resistance, resulting in colorless, odorless, and metal-free sulfur-containing polymers. This work comprehensively summarizes the fundamental research activities on the organocatalytic polymerization of COS(CS2) with epoxides, affording a variety of poly(thiocarbonate)s and poly(thioether)s with well-defined structures. The catalysis of several organic Lewis pairs, i.e. the trialkyl borane/ organic base and (thio)urea/organic base systems, for the polymerizations of COS(CS2) with epoxides is discussed in detail. Of significance, the conceptualization of O/S ER, a unique phenomenon in the copolymerization process of COS(CS2) with epoxides, guided us to have success in synthesizing a variety of poly(thioether)s. By inhibiting O/S ER, poly(monothiocarbonate)s have been developed by the catalysis of many organocatalysts. In addition, this study proposes the “supramolecular anion” strategy for the controlled copolymerization of COS with epoxides. This strategy can be expanded to the controlled polymerization of many types of monomers with heteroatoms (e.g., O, S, N) under the catalysis of organic Lewis pairs. The properties of the COS(CS2)-derived polymers including optical, electronic, crystalline properties are presented. Future efforts can be directed to the development of robust, versatile, highly active and stereoselective organocatalysts for the copolymerization of COS(CS2) with epoxides, as well as the synthesis of sequence-controlled sulfur-containing polymers.关键词：Organocatalyst;Sulfur-containing one-carbon monomers;Epoxides;Ring-opening copolymerization;Sulfur-containing polymers
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发布时间：2021-01-26 - 摘要：In recent years, Lewis pairs catalytic polymerization (LPP) has become one of the hot topics and attracted much attention in the field of polymer chemistry. Some exciting results were reported in polymer synthesis by using Lewis pairs, especially in the addition polymerization of polar vinyl monomers. Great successes were also achieved in the ring-opening polymerization (ROP) of cyclic esters and ring-opening alternating copolymerization (ROAC) of cyclic anhydrides/epoxides catalyzed by Lewis pairs, which provides a relatively simple and efficient approach for synthesizing polyesters with diverse structure and chemical modification of polyester materials. The synergistic effect between Lewis acid and Lewis base significantly improved the catalytic activity as well as the monomer adaptability. This work reviews the recent progress on Lewis pairs catalytic ROP and ROAC in our research group. We discussed the polymerization mechanisms, polymerization behaviors, and the relationships between structures of catalyst and catalytic performance in the ROP and ROAC catalyzed by Lewis pairs. The methodology was also introduced for construction of sequence-controlled polyesters by chemo-selective polymerization of mixed monomer feedstocks. Finally, novel Lewis pairs catalytic systems and methodologies were prospected for the stereo-selective polymerization of racemic monomer and the copolymerization of cyclic anhydrides and epoxides with five-membered rings such as tetrahydrofuran and 2-methyltetrahydrofuran.关键词：Aliphatic polyesters;Lewis pairs;Ring-opening polymerization;Ring-opening alternating copolymerization;Environment-friendly
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发布时间：2021-01-26 - 摘要：Poly(lactic acid), as a kind of biocompatible and degradable polymer, has considerable potential in a wide range of applications. Because the main chain repeating unit has a chiral center, its physical and mechanical properties are closely related to its stereoregularity. In recent years, chiral organocatalysts have attracted increasing attention in stereoselective ring-opening polymerization (ROP) of lactide in addition to organometallic catalysts with chiral centers. In this contribution, we synthesized three types of chiral ureas (L-Phe-U, L-Ala-U and L-Val-U), which were prepared by reactions of L-Phenylalanine methyl ester (L-Phe-OMe), L-alanine methyl ester (L-Ala-OMe) and L-valine methyl ester (L-Val-OMe) with 4-(trifluoromethyl)phenyl isocyanate. They can form binary catalytic system with DBU, which can catalyze the stereoselective ROP of rac-lactide (rac-LA) to produce stereoblock PLA (Pm up to 0.87) at room temperature. In addition, the stereoregularity (Pm) can be improved by reducing the polymerization temperature with regularity as high as 0.90 at −20 °C. Using 1H homonuclear decoupling spectroscopy, it was found that the contribution of chain-end control mechanism to stereo-regularity increased with decreasing temperature.关键词：Poly(lactic acid);Organocatalyst;Ring opening polymerization;Stereoselectivity
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发布时间：2021-01-26 - 摘要：Light can induce reversible solid-to-liquid transitions of some azobenzene-containing polymers (azopolymers). These kinds of azopolymers have photoswitchable glass transition temperature (Tg). Trans and cis isomers usually have different Tg. The Tg values of trans azopolymers are above room temperature, which are solids. On the contrary, cis azopolymers are liquid with Tg values below room temperature. Trans-to-cis isomerization occurs by UV irradiation. Visible light or heat can induce cis-to-trans isomerization. The performance did not change after dozens of reversible cycles. Compared with heat-induced solid-to-liquid transition, photoinduced reversible solid-to-liquid transitions have higher spatiotemporal resolution. The mechanism of solid-to-liquid transition was discussed in this article. Side-chain azopolymers are most studied up to now. The results show that the length of spacer and alkyl tail of an azopolymer is the key factor of whether it shows photoinduced solid-to-liquid transition. Different structures of main chain azopolymers also affect photo isomerization, which could be efficiently constructed by reversible addition-fragmentation chain transfer polymerization (RAFT), atom transfer radical polymerization (ATRP) and ring opening metathesis polymerization (ROMP). Azopolymers are widely used in self-healing materials, adhesives, photo-actuators, micro-actuators, transfer printing, nanoimprint, lithography,etc. In this feature article, recent progress of azopolymers in photoinduced reversible solid-to-liquid transitions is reviewed, their potential applications are demonstrated, and the remaining challenges in this field are discussed.关键词：Polymers;Azobenzene;Photoinduced solid-to-liquid transition;Glass transition temperature;Photoresponsive
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发布时间：2021-01-26 - 摘要：With the emerging demand of environmental protection and sustainable development, devices that can perform clean, efficient, and inexpensive energy conversion (e.g., alkaline fuel cells, water electrolysis, redox flow batteries, etc.) have attracted increasing attention. Anion exchange membranes (AEMs) are a class of solid polyelectrolytes that are key components in the above-mentioned alkaline energy conversion devices to transport hydroxide anions. Two of the key properties of AEMs are ionic conductivity and alkaline stability, as they are directly related to the efficiency and durability of the devices, respectively. The AEMs bearing polyethylene backbones (PE-AEMs) have outstanding chemical stability, good compatibility with various cations, and strong mechanical properties, and thus they become promising candidates for high-performance AEMs. In this account, we summarize the synthetic strategies of PE-AEMs, which include ring-opening-metathesis polymerization (ROMP) followed by hydrogenation, derivatization of poly(ethylene-co-styrene), direct copolymerization of functionalized terminal alkenes with ethylene, and radiation graft to modify polyethylene films. Among all these strategies, we specifically focus on the development of sequential cyclooctene ROMP and hydrogenation strategy, as it has the advantages of well-defined polymer structures, precise control of functionality distribution, and excellent tolerance to diverse functional groups. We also evaluate the structure-property relationship of the resultant PE-AEM membranes and discuss the future of these materials.关键词：Anion exchange membrane;Polyethylene;Synthetic strategy;Alkaline stability
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发布时间：2021-01-26 - 摘要：A vinyl monomer 1-(4-vinylbenzyl)-indole was prepared in 90% yield through one-step synthesis by using commercially available starting material. The reversible addition-fragmentation chain transfer (RAFT) polymerization of 1-(4-vinylbenzyl)-indole was performed with 2,2-azobisisobutyronitrile (AIBN) as initiator and 2-phenyl-2-propylbenzodithiolate as chain transfer agent (CTA), furnishing a series of polystyrenes containing indole side groups with adjustable molecular weight (Mn = 5200 – 18500 g/mol). With the catalysis of B(C6F5)3, post-polymerization modification of the produced polymers could be achieved through the regioselective silylation of their indole side groups with different hydrosilanes. Analysis of the polymers by GPC and 1H-NMR spectroscopy revealed that the C3-position of indole group at the polystyrene side chain was selectively silylated while the polymer backbone was maintained. The employment of the less sterically crowded PhMe2SiH or silanes containing tetraphenylethene (TPE)-moiety as silane sources led to the production of polymers with 50% or 38% grafting ratio of silylated indole, respectively. Moreover, silanes containing tetraphenylethene (TPE)-moiety would endow the resultant polymer with the aggregation-induced emission feature. Under UV irradiation, almost no fluorescence was observed for polymer containing TPE-moiety dissolved in THF. The addition of large amounts of hexane to THF led to the observation of a relatively strong blue fluorescence. With an increase in the hexane fractions (fw) of mixed solvents, the corresponding fluorescence intensity gradually increased until reaching the maximum value at fw of 90%, which is approximately 57-fold higher than that in pure THF solution.关键词：Post-polymerization modification;Indole side group;C―H silylation;B(C6F5)3;Aggregation-induced emission
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发布时间：2021-01-26 - 摘要：Tumor microenvironment responsive polymeric nanomedicines significantly improve the specific release of drugs at tumor sites, which can reduce side effects to the normal tissues. However, the poor cellular uptake ability of most PEGylated nanodrugs has reduced much of the antitumor efficacy. Therefore, it’s probably easy to imagine that after specific drug release of nanomedicines at tumor sites, the antitumor efficacy could be significantly improved with the enhancement of the drugs’ cellular uptake ability. Herein, a drug delivery system that can enhance drug endocytosis and respond to tumor microenvironment is reported. In this study, rhodamine B was bonded with arginine methyl ester to give guanidinium rhodamine B (RhoB-Gu), and 4-(hydroxymethyl) phenylboronic acid pinacol ester (HAPE) was bonded with poly(L-glutamic acid)-graft-poly(ethylene glycol) to obtain reactive oxygen species (ROS) responsive nanocarrier, PgP-HA. Then the RhoB-Gu was loaded into PgP-HA as a model drug to obtain ROS responsive core-shell polymeric nanoparticles, PgP-HA/RhoB-Gu NPs. The nanoparticles formed a stable core-shell structure due to the electrostatic assisted hydrogen bonding between carboxyl group of PgP-HA and guanidine group of RhoB-Gu, the electrostatic interaction between tertiary amines of RhoB-Gu and carboxyl group of PgP-HA, as well as the hydrophobic interaction of HAPE segments. Furthermore, in vitro release test showed that the PgP-HA/RhoB-Gu NPs could achieve about three fold drug accumulation release in PBS contained 1.0 mmol/L H2O2 than in PBS without H2O2, and the particle size also increased with the increasing concentration of H2O2, which indicated that the PgP-HA/RhoB-Gu NPs have highly sensitive response to ROS. Meanwhile, in vivo distribution results showed that the PgP-HA/RhoB-Gu NPs realized drug enrichment at the tumor sites, and the model drug, RhoB-Gu, showed higher cellular uptake than original RhoB, revealing good potential to expand the application on traditional chemotherapy drugs. This work provides an effective strategy of nanodrugs to improve the efficacy through ROS responsive release at tumor sites and cellular uptake increase simultaneously.关键词：Polymer nanocarrier;Reactive oxygen species responsive;Intracellular delivery
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发布时间：2021-01-26 - 摘要：Porous carbon materials (PCMs) have drawn wide attention in gas adsorption and energy storage due to their large specific surface areas, physical and chemical stability and structural diversity. Doping heteroatoms such as nitrogen species has been considered as a reasonable method to enhance the application performance of PCMs by improving the interactions between PCMs and adsorbates. However, heteroatom-doped PCMs prepared with traditional methods such as chemical activation have disadvantages of broad pore size distribution and difficulty in accurately locating heteroatoms on the skeleton of PCMs, thus limiting their applications in gas adsorption and energy storage. Conjugated microporous polymers (CMPs) with excellent structural controllability and permanent microporous properties are considered to be a new choice for the preparation of PCMs. In this work, two nitrogen-doped PCMs with different structural units were prepared by using CMPs as the precursors. First of all, two CMPs (TNCMP1, TNCMP2) were synthesized by Pd-catalyzed Suzuki coupling reaction. Then the CMPs were pyrolyzed at 700 °C to give two PCMs (C-TNCMP1, C-TNCMP2). The effects of carbonization and planarity adjustment on carbon dioxide (CO2) adsorption and supercapacitor performance of the PCMs were studied. Compared with their precursors, the obtained PCMs exhibit narrower pore size distribution and higher microporosity up to 93%. Thus, both of the PCMs show higher CO2 adsorption ability than their precursors, among which the CO2 adsorption capability of C-TNCMP1 is up to 3.19 mmol/g. Compared with C-TNCMP1, C-TNCMP2 with better structural planarity has larger graphite nitrogen content of 57.39 at% and higher conductivity of 3.89 × 10−5 S/m, thus showing better supercapacitor performance. C-TNCMP2 exhibits a decent specific capacitance of 219 F/g at the current density of 0.1 A/g and a good rate capability at high current density. This work could provide a rational principle for the preparation of high performance porous carbon materials for the applications of gas adsorption and energy storage.关键词：Porous carbon materials;Nitrogen doping;Carbon dioxide adsorption;Supercapacitor
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发布时间：2021-01-26 - 摘要：Polyimide films have been successfully applied as cable insulation layer, optical fiber coating, printed circuit board and flexible solar cell substrates, owing to their excellent heat resistance and mechanical properties. During the devices fabrication and application, the polyimide films are usually exposed to elevated temperature or thermal oxidation environment, which often causes material degradation and results in device failure. Therefore, it is necessary to understand the thermo-oxidative degradation behavior of polyimide films in order to improve the reliability of the materials. The thermo-oxidative degradation of polyimide film was a multi-step process. It can not be described by one kinetic triplet, i.e., the apparent activation energy E, reaction model f(α) and pre-exponential factor A. In this study, the multi-step thermo-oxidative degradation of polyimide film derived from PMDA and ODA was investigated based on its thermogravimetirc curves under different linear heating rates. The overlapped processes incorporated in the overall thermo-oxidative degradation were firstly separated by peak-fitting of the differential thermogravimetric curves of polyimide film using Fraser-Suzuki function. Kinetic analysis of each separated process was subsequently conducted by employing Friedman method and Master-plots to determine the E, f(α) and A. The kinetic result revealed that two overlapped processes were involved in the overall thermo-oxidative degradation of polyimide film. The E values for the two processes were 154.00 and 139.27 kJ/mol respectively. The corresponding lnA values were 18.55 and 16.74 s−1. Both the two processes followed the Avrami-Erofeev model. Moreover, the validity of these kinetic parameters obtained were verified by reconstruction of original TGA curves and prediction of TGA curve not employed in the kinetic analysis.关键词：Polyimide film;Thermo-oxidative degradation;Multi-step process;Kinetics;Prediction
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发布时间：2021-01-26 - 摘要：Polynorbornene (PNB) is a kind of smart material with excellent shape memory performance. The appearance of PNB is powder, so it can only be processed by adding plasticizing oil. In order to broaden its processing method and avoid environmental pollution caused by aromatic oils containing benzene, microcrystalline wax (MW) can be used as a better choice for plasticizing oil. Therefore, PNB/MW materials were prepared by using PNB as the matrix and adding microcrystalline wax with different contents. The basic properties of PNB/MW materials were studied by Shore D hardness tester, polarizing microscope, differential scanning calorimeter (DSC), universal electronic tensile testing machine and dynamic mechanical analysis (DMA). The dual-shape memory and reversible plasticity shape memory properties of PNB/MW materials were studied by DMA-Q800. The results showed that the glass transition temperature (Tg) of PNB is adjusted to near room temperature by microcrystalline wax, which was beneficial to the reversible plasticity deformation. So MW could replace treated distillate aromatic extract (TDAE) for the processing of PNB because of its non-pollution. The elongation at break of PNB/MW materials was more than 200%, and the tensile strength was high. The high elongation at break was beneficial to the deformation and recovery of the shape memory. In addition, the wide solid-liquid transition of microcrystalline wax also played the role of reversible phase, which made the recovery process controllable. The movement of PNB chain segment was limited by solid microcrystalline wax, which contributed to the fixation process of reversible plasticity shape memory. It was concluded that PNB/MW50 had excellent dual-shape memory and reversible plasticity shape memory performance.关键词：Polynorbornene;Microcrystalline wax;Reversible plasticity;Shape memory
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发布时间：2021-01-26
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