最新刊期
卷 52 ， 期 5 ， 2021
- 摘要：Rare earth (RE) catalysts exhibit extremely high catalytic activity in ring-opening polymerization. This work reviews the application of rare earth catalysts in ring-opening polymerizations of lactones, lactides, cyclic ethers, cyclic carbonates and cyclic carboxyanhydrides in the past decade. Compared to other transition metals and main group elements, RE elements have larger cationic radii which allow for higher coordination numbers and more coordination modes, endowing RE catalysts with high catalytic activity. These characteristics not only fuel the widespread use of new RE catalysts in pursuing high molecular weight and polymerization rate of intensively studied monomers, such as ε-caprolactone (CL), lactide (LA) and β-butyllactone (BBL), but also unleash the polymerization of traditionally non-polymerizable γ-butyrolactone (γ-BL) and its derivatives. The inherent low strain energy of the five-membered ring imparts monomer recyclability into the corresponding polymer. Furthermore, stereoselective polymerization of racemic monomers can be realized by RE catalysts containing chiral ligands with large steric hindrance. Slight modification of ligands gives rise to tailored or even inverted stereoregularity of polymers. The unique advantages of RE catalysts in the controllability of polymerization process and polymer structure are illustrated by discussing the relationship between catalyst structures and polymerization results. In addition, a novel ring-opening polymerization catalyzed by RE compounds, named Janus polymerization is introduced. This new mechanism combines cationic and anionic polymerizations at two ends of a single propagating chain and thus provides a facile methodology to synthesize polymers with sophisticated chemical structures and topologies in one step. New catalysts and mechanisms of ring-opening polymerizations have attractive potentiality in begetting new materials.关键词：Rare earth catalysis;Ring-opening polymerization;Stereoselective polymerization;Polyesters;Polyethers;Polycarbonates;Poly(α-amino acid)s;Janus polymerization
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发布时间：2021-05-07
Reviews
- 摘要：Polymer science has played an increasingly important role in human life and modern society. Therefore, it is imperative to understand its structure-function relationship and properties deeply. Modern instruments are limited byex situ and miscellaneous sample preparation, and display “darkness” in the testing process. Fortunately, fluorescence imaging technology has received considerable attention owing to its capacibity to visualize the variation of structure and morphology in materials. Traditional dyes suffer from aggregation-caused quenching effect, significantly restricting its practical applications. In contrast, due to the advantages of high fluorescence quantum efficiency and extreme sensitivity to external stimuli, aggregation-induced emission (AIE) technology has become a forefront of chemistry and materials. This account systematically summarizes how the unique molecular visualization technology based on the working principles of AIE can become a new method for in-situ study of polymer science: monitoring polymer solution properties, such as polymerization process, solubility parameters and structure-activity relationship; visualizing the polymer aggregate properties, such as solid-state segmental movement, glass transition, phase separation and crystallinity, etc. At last, the future development in this field has prospected.关键词：Aggregation-induced emission;Polymer science;Visualization;Fluorescence probe
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发布时间：2021-05-07
Feature Articles
- 摘要：In this work, we report an orthogonal preparation of polyvinyl-block-polyester copolymers in a one-pot and single step strategy via a well-defined β-diiminate zinc ((BDI)Zn) catalyst under light irradiation. The zinc compound is specially designed to possess 2-bromoisobutyrate initiating group, which combines the capabilities of ring-opening polymerization (ROP) of lactones and atom transfer radical polymerization (ATRP) of vinyl monomers. Under light, simultaneous chain propagations via a coordinated insertion of cyclic esters from Zn-oxygen bond and organocatalyzed-ATRP of vinyl monomers from the ω-bromoisobutyrate take place simultaneously, thus providing an extremely efficient route to block copolymers composed of polyester and polyvinyl in single step. The structure of the catalyst is established by single-crystal X-ray diffraction, 1H- and 13C-NMR. A wide range of polyvinyl-block-polyester copolymers including polystyrene-block-polylactide (PS-b-PLA), poly(methyl methacrylate)-b-PLA (PMMA-b-PLA) and PS-b-polycaprolactone (PS-b-PCL) with controlled molecular weight and compositions are efficiently constructed. These block copolymers display monomodal and moderate molecular weight distributions (Mw/Mn<1.5), and are fully characterized by DSC,1H-NMR, and 13C-NMR spectroscopy. The catalyst and synthetic strategy mentioned above offer an extremely convenient catalytic access to polyvinyl/polyester block copolymers for the formation of attractive nanomaterials.关键词：Block copolymer;Orthogonal polymerization;One-pot;Light irradiation;β-Diiminate zinc
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发布时间：2021-05-07 - 摘要：The limited distribution of anticancer nanodrugs remains a bottle-neck for their therapeutic effect. Several strategies, such as surface modification, photothermal activation, and microenvironment modulation, have been studied to improve the penetration of anticancer drugs in solid tumours. However, the inherent high osmotic pressure, high cell density, lack of blood supply, and other biological barriers in solid tumors make it difficult for nanomedicine to infiltrate in the tumors, thus inaccessible to the distal cells to exert an effective therapeutic effect. Therefore, the way to deliver sufficient drugs to infiltrate in a tumour is a key problem that should be solved quickly. Herein, we constructed a molecularly precise polylysine-dendrimer-drug conjugate with γ-glutamyl transpeptidase (GGT)-sensitive termini and obtained a zwitterionic γ-glutamyl functionalized dendrimer-drug conjugate, i.e., G4/CPT-BGA. The results showed the molecular weight of G4/CPT-BGA dendrimer was 20 kDa with a small size of 5 nm and a moderate surface charge of −2 mV. The G4/CPT-BGA could undergo rapid GGT-triggered charge-reversal from zwitterionic to cationic, thereby quickly endocytosed by tumor cells, releasing the conjugated drug (CPT) to exert effective cytotoxicity. The in vitro endocytosis and exocytosis experiments showed that G4/CPT-BGA was able to traffic in cells through a caveolae-mediated pathway, then traffic out of cells via Golgi-apparatus, thus achieving active transcytosis for transcellular delivery. The tumor penetration ability of G4/CPT-BGA was investigated using three-dimensional multicellular spheroids, which showed G4/CPT-BGA could evenly distribute throughout the spheroids via transcytosis-mediated active tumour infiltration. Therefore, a simple modification of the cationic dendrimer with GGT responsive zwitterionic γ-glutamine enables the dendrimer to actively transcytosis across cells, thereby avoiding the paracellular diffusion obstacles, which may also be applicable for designing anticancer nanomedicine systems with enhanced penetration ability.关键词：Nanomedicine;Dendrimer;Tumor penetration;Active transcytosis;γ-Glutamyl transpeptidase
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发布时间：2021-05-07 - 摘要：Soybean oil-based diols (SOD) can be synthesized from soybean oil and polymerized with diacids to give soybean oil-based polyesters. However, the conventional esterification and transesterification mechanisms of polycondensation are incapable of obtaining high molecular weight (HMW) soybean oil-based polyesters due to the kinetic deviation of diol/diacid unit ratio from 1∶1, which is required for producing HMW polyesters. Here we introduce a novel carboxyl-ester transesterification (CET) mechanism to synthesize HMW soybean oil-based polyesters through melt polycondensation. Using excess diacids to esterify with SOD, a carboxyl-terminated prepolymer was first afforded. Then the excess diacids were regenerated via CET and removed through sublimation, thus dynamically approaching the stoichiometric condition of the diol/diacid unit, through which a series of HMW soybean oil-based polyesters with viscosity-average molecular weights up to 123 kDa were obtained. The resultant polyesters exhibit good thermal stability and high transparency, and their adhesive performances are comparable to those of commercial pressure-sensitive adhesives. Furthermore, antibacterial soybean oil-based polyesters were achieved via thiol-ene “click” reaction of the alkene groups in the aliphatic side chain of polyesters with a thiolated quaternary ammonium salt.关键词：Carboxyl-ester transesterification;Melt polycondensation;Vegetable oil;High molecular weight polyester;Pressure-sensitive adhesive
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发布时间：2021-05-07 - 摘要：The alternating copolymerization of carbonyl sulfide (COS) with epoxides is an emerging approach to the synthesis of sulfur-containing polymers. Epichlorohydrin (ECH) is a low-cost, commercially available epoxide rich in chloride. The copolymerization of COS with ECH can afford a unique poly(monothiocarbonate) (PMTC) containing chloride and sulfur atoms that could be a functional material. In this work, we report for the first time the alternating copolymerization of COS and ECH using metal-free catalysts. A binary catalytic system consisting of triethyl boron (TEB) and Lewis base (e.g. PPNCl, NBu4Cl, PPh4Cl, PPh4Br, DTMeAB and DBU) afforded PMTCs with completely alternating structures (i.e., alternating degree >99%), the head-to-tail diad content >99%. The effect of various experimental conditions including the types of organic Lewis acid-base pairs, reaction temperatures, feeding ratios on the copolyemrization were investigated through controlled experiments. The combination of TEB/PPNCl (molar ratio of 2/1) could effectively catalyze the copolymerization of COS with ECH at 0 °C, with ECH conversion up to 92%, and produce the copolymer with number-average molecular weight ( Mn) of 3000 g/mol that is comparable to the previous result via bifunctional metal catalyst. Although it is still a big challenge to obtain ECH/COS copolymer with high molecular weights, this work also discovers that organic Lewis pairs could efficiently achieve fully alternating oligomers with Mn less than 1000 g/mol at 30 °C, providing a new option for high value-added utilization of COS and ECH.关键词：Carbonyl sulfide;Epichlorohydrin;Alternating copolymerization;Metal-free catalysis
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发布时间：2021-05-07 -
MoS2 Membranes with Photothermal Conversion Property for Nanofiltration and Antibacterial Activity 增强出版
摘要：Assembly of two-dimensional nanosheets has been demonstrated as one of the promising strategies to construct laminar membranes for efficient nanofiltration of dyed wastewater and even brackish water. However, these membranes are usually confined by poor stability and inferior salt rejection imposed by their loose laminar structure. Large majority of them also have complex preparation procedures and excessive feedstock consumption. Herein, new laminar nanofiltration membranes are designed to fundamentally overcome the conventional limitations. The membranes are prepared by leveraging trimesoyl chloride (TMC) dissolved in n-hexane, on the assembly of tannic acid-functionalized molybdenum disulfide (MoS2) nanosheets aqueous solution (TAT-MoS2). The interfacial polymerization reaction between TMC and TAT-MoS2 takes place on polyacrylonitrile (PAN) substrate with its pH of 12. As-prepared laminar nanofiltration membranes display extraordinary stability in diverse harsh environments. The dense cross-linking network formed by acyl chloride group and MoS2 nanosheets contributes to appropriate membrane pore size. Therefore, the laminar nanofiltration membranes promoted rejections against Na2SO4 (≈85%) and negatively charged dyes (>98.5%). In the meanwhile, the membranes possess high selectivity for dyes from saline solutions, which shows huge potential in industrial production (NaCl<15%). Furthermore, MoS2 nanosheets endows the laminar nanofiltration membranes with remarkable photothermal effect under near infrared light irradiation. As the membrane surface temperature rose, the bacteria, one of the membrane fouling culprits, would find it harsh to survive. As dead bacteria are more easier to be rinsed over membrane surface, the laminar nanofiltration membranes retain self-cleaning function. Antibacterial capability provides a fresh solution for designing membranes which work in bacteria-rich workspaces, holding significant potentials in practical applications.关键词：Two-dimensional nanosheets;Laminar membrane;Nanofiltration;Photothermal effect;Antibacterial activity- 231
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发布时间：2021-05-07 -
Chain Shuttling Copolymerization of Ethylene and Styrene Catalyzed by Rare-earth Metal Complexes 增强出版
摘要：As a facile strategy for one pot synthesis of multiblock polymers, chain shuttling polymerization has aroused considerable attention. However, the construction of the corresponding catalytic system is difficult, leading to the limited number of monomers to successfully achieve chain shuttling polymerization. Herein, we conducted the investigation of chain shuttling polymerization of ethylene and styrene on the basis that in the presence of AliBu3, rare-earth metal complex 1 catalyzed the copolymerization of ethylene and styrene to give the alternating sequence enriched copolymer with the chain transfer efficiency of 100%. Firstly, complex 2 was employed to catalyze the copolymerization of ethylene and styrene. The styrene content of the afforded copolymer is less than 4%. Thus, ethylene polymerization was conducted under various ratios of [Al]0 to [2]0. The molecular weight of the afforded polyethylene exponentially decreased with the increase of [Al]0/[2]0 with the power of −0.778, suggesting that the chain transfer efficiency is less than 100%. The ternary catalytic system composed of 1, 2 and AliBu3 catalyzed the copolymerization of ethylene and styrene to afford copolymers with bimodal molecular weight distributions, indicating the unsuccess of chain shuttling. Then after screening a series of complexes, 3 was found to catalyse the copolymerization of ethylene and styrene with the chain transfer efficiency of 100% as the molecular weights of the afforded copolymers syndiotatic polystyrene sequence enriched exponentially decreased with the increase of [Al]0/[3]0 with the power of −1.097. When the ratio of [AliBu3]0 to [1+3]0 was no less than 20, the ternary catalytic system composed of 1, 3 and AliBu3 catalyzed the copolymerization of ethylene and styrene to afford multi-block copolymers containing alternating sequences and syndiotactic polystyrene sequences with unimodal molecular weight distributions, indicating the success of chain shuttling. The sequence distribution was effectively controlled by adjusting the ratio of 1 to 3.关键词：Chain shuttling polymerization;Rare-earth metal complex;Sequence control polymerization;Ethylene;Styrene- 162
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发布时间：2021-05-07 - 摘要：Catalytic ethylene-conjugated diene copolymerization could be a new route of preparing functionalized polyolefins and degradable polyolefins. In this work a MgCl2-supported Ziegler-Natta catalyst containing internal electron donor was used to catalyze copolymerization of ethylene and isoprene (Ip). Under 1.01×105 Pa ethylene pressure and 0−2 mol/L initial Ip concentration ([Ip]0), the copolymerization product was composed of two fractions with remarkably different chain structures: one fraction with <2 mol% Ip content and high molecular weight, and the other fraction with >20 mol% Ip and low molecular weight. More than 75% of Ip units in both fractions had trans-1,4-configuration, showing high regio/stereo selectivity of the copolymerization. Copolymerization activity increased when [Ip]0 was raised from 0 mol/L to 1 mol/L, and decreased with further increase of [Ip]0 to 2 mol/L, meanwhile the fraction of high Ip content increased with [Ip]0. Copolymerization using TIBA as cocatalyst showed higher catalytic activity than using TEA, slightly lower Ip incorporation rate and narrower molecular weight distribution. Adding siloxane type external electron donor in the polymerization system strongly reduced the fraction of high Ip content, converting the bimodal composition distribution into monomodal one with the low Ip content copolymer as the major component.关键词：Ziegler-Natta catalyst;Ethylene;Isoprene;Copolymerization
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发布时间：2021-05-07 -
Systematic Study of Fluorine Effect on
α -Ketiminato Nickel Catalyzed Ethylene (Co)Polymerization 增强出版摘要：Compared with steric bulk and electronic effect in transition metal catalysts for olefin coordination-insertion polymerization, fluorine effect is one facile and effective method for modulating olefin polymerization reaction. However, study on fluorine effect in late transition metal catalysts is relatively less. In this contribution, by installation of fluorine atoms with different sites and numbers into N,O-type single-component cationicα-ketiminato nickel catalysts, fluorine effect on ethylene polymerization properties was comprehensively investigated, including catalytic activity, thermal stability of catalyst, polymer molecular weight, and branching density. These new nickel catalysts were fully identified by 1H-NMR and 13C-NMR spectroscopy, elemental analysis, and X-ray diffraction analysis. It was fully found that the ortho-fluorinated substituent in the nickel catalyst obviously favoured the enhancement of polymer molecular weight (weight-average molecular weight (Mw): up to 26.2×104 g·mol−1), but the meta- and para-fluorinated substituents in the nickel catalysts reduced the catalytic activity; especially the perfluorinated substituent in the nickel catalyst not only decreased the thermal stability of catalyst, but also led to the drop of activity and molecular weight. It was completely different from the previously reported effect of fluorine on these catalytic systems such as fluorinated phenoxy-imine nickel and titanium catalysts. Notably, the non-fluorinated nickel catalyst was inactive for the copolymerization of ethylene and methyl acrylate (MA), but the ortho-fluorinated nickel catalyst showed activity and enabled the incorporation of comonomer (0.9 mol%), albeit with low activity. However, the ortho-fluorinated nickel catalyst was also inactive for other more challenging monomers such as methyl methacrylate (MMA), acrylic acid (AA), vinyl acetate (VA) and n-butyl vinyl ether (BVE). As expected, the long chain polar monomers such as 6-chlorohex-1-ene, methyl 10-undecenoate (UA), undecenoic acid (UCOOH) and 10-undecen-1-ol (UOH) exhibited better copolymerization behaviors using theortho-fluorinated nickel catalyst. This work will help the community to understand the crucial role of fluorine effect in olefin polymerization.关键词：Fluorine effect;Olefin polymerization;Late transition metal catalysts;Polar monomers;Imino-ketone- 242
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发布时间：2021-05-07 - 摘要：Copolymerization of butadiene (Bd)/isoprene (Ip) and Bd/Ip/myrcene (My) was carried out with Nd(vers)3/Al(i-Bu)2H/AlEt3/EASC catalyst system. For the BD and Ip copolymerization, the catalyst content has rare effect on the copolymer composition and the unit content in copolymer was almost proportional to the monomer feed; only one glass transition temperature (Tg) was detected by DSC and it increased linearly with the increasing Ip unit content in copolymers, which indicated the random structure of copolymers. The reactivity ratios of butadiene (r1) to isoprene (r2) were calculated with both Fineman-Ross and Kelen-Tüdos method. r1 and r2 were close to 1, suggesting random copolymerization of Bd and Ip with the present catalyst system. The structure and distribution of copolymer sequences were analyzed and assigned with 13C-NMR. The number average sequence lengths calculated by 13C-NMR and Bernoullian/Markov model, respectively, were compared, and the result showed that Markov model was more suitable for simulating the copolymer sequence distribution. Ternary copolymerization of Bd, Ip and My catalyzed by the catalyst system showed that the My unit content in the copolymer increased with the monomer feed, only one glass transition was detected and the value slowly increased with the increasing My unit content in copolymers. The reactivity ratios calculated by Kelen-Tüdos method were r12=1.03, r21=1.69, r23=1.11, r32=3.62, r13=0.80, r31=4.67.关键词：Butadiene-isoprene copolymer;Neodymium-based catalyst;Myrcene;Reactivity rate;Sequence distribution
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发布时间：2021-05-07
Research Article
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