最新刊期
卷 ， 期 8 ， 2017
- 摘要：Application of polymer based composites with positive temperature coefficient (PTC) effect is greatly limited because of the drawbacks such as slow change of the resistivity in the transition temperature range, low PTC intensity, poor PTC reproducibility. In this work, the composite composed of polyvinylidene fluoride (PVDF) as matrix and carbon fiber (CF) as conductive filler was prepared by melt mixing to obtain high PTC intensity and stable reproducibility of PTC effect. The resulted PVDF/CF composites, with CF content from 13.1 vol% to 18.2 vol%, which was above the percolation threshold of 3.93 vol%, showed remarkable PTC effect without significant negative temperature coefficient (NTC) effect during heating processed. A fast transition from conductor to insulator was obtained when the temperature was close to the melting point of PVDF matrix, namely, the increase rate of volume resistivity was 1.3×105 Ω cm K-1 in the transition temperature range (155.5-171.0℃). To our knowledge, this study is the first to report such phenomena in CF filled composites. The transition temperature ranges for all composites, determined by the melt temperature range and melting point of PVDF matrix, were almost the same owing to the presence of CF, and showed no effect on the crystallization behaviour of PVDF matrix. The room temperature resistivity and PTC intensity of composites with low CF content showed dependences on the thermal-cooling cycles, but they showed almost the same pattern and PTC intensity for the composites with high CF content. Desired reconstruction of CF network in the PVDF melt during cooling process and the excellent PTC reproducibility were observed even after 9 thermal-cooling cycles.关键词：PVDF;Carbon fiber;Conductive composite;Positive temperature coefficient effect;Transition temperature range
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发布时间：2021-01-26
Rapid Communications
- 摘要：Ion-containing polymers refer to polymers with covalently bonded ionic groups. The strength of ionic interaction relies on the ionic species as well as the polarity of their surrounding medium, and thus can be tuned in a wide range. When the energy approaches the thermal energy, association and dissociation of the ionic interaction would enter a time window of our observation and thus the interaction becomes reversible. The reversibility enables the ion-containing polymers to exhibit rich rheological and dielectric properties, so as to be applied in varied novel materials including impact-resistant, shape-memory, self-healing and intelligent materials. This review highlights recent progresses on understanding the structure-property relationship and molecular rheology of the ion-containing polymers. Part I summarizes a relationship between the association status and interaction energy of ions and/or ionic dipoles. In particular, definitions of ionomer and polyelectrolyte have been given on a basis of relative strength of the electrostatic interaction and thermal energy. Morphological and dynamic changes have been explained along with an ionomer-to-polyelectrolyte transition though introducing polar solvent into an ionomer. Part Ⅱ summarizes evolution of linear viscoelasticity of random ionomers (in which the ionic groups are randomly distributed) with the ion content. Particular interests have been placed on a sol-gel transition that occurs at averagely~one ion per chain and completed at averagely~two ions per chain for non-entangled random ionomers, and a single-to-double plateau transition that occurs at averagely~one ion per entanglement for entangled random ionomers. Both the theoretical and experimental developments have been summarized with respect to the improved understanding of the two transitions. Part Ⅲ summarizes the ion transportation within the ion-containing polymers, in particular molecular design to soften the ionic interaction as well as to increase the ion mobility, both should enhance the ion conductivity so as to facilitate the application of the ion-containing polymers in fields like ion battery separator membranes and ion-transport actuators.关键词：Ionomer;Polyelectrolyte;Single-ion conductor;Association energy;Reversibility;Linear viscoelasticity
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发布时间：2021-01-26 - 摘要：Cationic polymers were widely used as non-viral gene carriers, however, the transfection efficacy and cytotoxicity of these polymers are strongly associated with each other, that is high transfection efficacy is usually accompanied by serious toxicity. How to prepare polymeric carriers with high transfection efficacy and low toxicity is a key challenge in clinical gene therapy. Fluorinated polymers are a new class of non-viral gene carriers with interesting physicochemical properties. Fluoroalkyl substances have unique properties compared to traditional alkyl lipids. They are both hydrophobic and lipophobic, but prefer to associate with other fluorous compounds via a fluorophilic effect. As a result, fluorinated polymers with low critical aggregation concentrations can efficiently condense nucleic acids into stable complexes at an extremely low nitrogen to phosphorous ratio or polymer dose. Fluorous ligands such as fluoroalkyls are beneficial for improved serum stability, cellular uptake, endosomal escape, and intracellular nucleic acid release, endowing the fluorinated polymers with a specific fluorous effect in gene delivery. The fluorinated polymers possess excellent self-assembly property and combine the features of cationic polymers and liposomes in gene delivery, for example, the high tissue penetration capability of cationic polymers, and self-assembly behavior and high gene transfection efficacy of cationic liposomes. The self-assembled fluoropolymers show excellent serum resistance due to the bioinert property of fluoroalkyl chains. They exhibit high gene transfection efficacy even in medium containing 50% serum, and thus present promising potential for clinical gene therapy. Compared to traditional alkylated materials, fluorinated polymers show more efficient cellular internalization and less toxicity due to reduced intermolecular interactions with the phospholipids in cell membrane. This feature article summarized recent advances of fluorinated polymers in gene delivery. The transfection efficacy and mechanism of fluorinated polymers in gene delivery, as well as their applications in gene therapy and gene editing were discussed. Finally, future perspectives of fluorinated polymers in gene delivery, protein and peptide delivery and other biomedical fields were given.关键词：Fluorinated polymers;Gene delivery;Fluorous effect;Dendrimers;Supramolecular assembly
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发布时间：2021-01-26 - 摘要：Conjugated polymers have demonstrated promising applications in fields of organic field-effect transistors, organic solar cells and organic light-emitting diodes, etc., due to their attractive advantages of unique optoelectronic properties, light weight, low cost and easy processability. However, regardless of the remarkable development for conjugated polymer materials and devices over the past decades, charge transport in conjugated polymers still remains unclear, which is mainly due to the molecular weight polydispersity and intermolecular entanglements of conjugated polymers as well as their naturally disordered structures in films. To achieve better understanding of the nature charge transport in conjugated polymers, continually increasing the molecular orders and reducing grain boundaries and defects are crucial. Aiming at this point, we propose a concept of multilevel charge transport investigation in conjugated polymers, and under this guideline, we have carried out systematical studies over the past years. In this article, we briefly summarize our recent results on charge transport investigation in conjugated polymers from macro-, to micro/nano-and molecular scales. With a derivative of poly(paraphenylene ethynylene) with thioacetyl end groups (TA-PPE) selected as an example, we found that the charge transport property could be significantly improved by 3-4 orders by continuously increasing the molecular orders in solid state. With downscaling to molecular scale, some new phenomenon was observed for conjugated polymers, such as the modulation of the redox center of tetrathiafulvalene (TTF) units on tunneling charge transport. In part 2 of the paper, combining the recent progress in literature, we give a detailed demonstration on the development history of conjugated polymer single crystals, with special emphasis on our efforts carried out in this field. Based on the investigation of polymer single crystals, a novel molecular packing model is found in the polymer micro/nanowires, that is the conjugated polymers aligned along the long-axis of nanowires, and the investigation of intrachain and interchain charge transport is achieved based on an individual conjugated polymer crystal, which is an important step in this filed. Finally, a short outlook is provided with regard to the concerns and the opportunities for the future studies on the multilevel properties and the devices of the conjugated polymers.关键词：Conjugated polymers;Multilevel solid state structures;Conjugated polymer single crystals;Intrinsic property;High performance devices
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发布时间：2021-01-26
Feature Articles
- 摘要：Block copolymers (BCPs) are a kind of copolymers containing homopolymer blocks that are chemically bonded together. They can undergo microphase separation (i.e., self-assembly) to form well-defined nanostructures (e.g., spheres, cylinders, vesicles, etc.), since their non-compatible blocks are covalently bonded, limiting the macrophase separation. The self-assembled nanostructures possess great potential for various applications in the fields of nanolithography, photonic crystal, data storage, drug delivery and controlled release, diagnostics and others. When imposing spatial constrains on BCPs, where the confining volume has at least one dimension comparable to the period (L0) of the bulk copolymer phase, a large variety of novel BCP assemblies (e.g., helix, patchy, staking, and other complex structures) can be generated under confined space due to the symmetry breaking, interfacial interactions, structural frustration and confinement-induced entropy loss. Recently, the fabrication of confined assemblies of BCPs and investigation of the BCPs assembly in different confined geometries from experimental and theoretical simulation points have been a topic of great interest in the scientific communities in China. This review aims to summarize some research progress on confined assembly of BCPs in China, including the general concept of confined assembly of BCPs, experimental and simulative investigation of confined assemblies of BCPs through varying factors under different dimensions, and potential applications of confined BCP assemblies. Factors affecting the confined assembly of BCPs, including the degree of confinement ( D/L0, D is the size of confinement space), interfacial interaction (selective or neutral interface), geometry of the confining space, block ratio, topology structure of the BCPs, and others, are also discussed. Moreover, compared with one dimension (1D) and 2D confinement, 3D confinement provides the most tightly confining geometry (i.e., highest confinement degree) and presents an enclosed surface around the BCPs, which may facilitate to easily manipulate new morphologies of the confined assembles and will attract more attention on this topic. To push forward the studies of the confined assembly of BCPs, the conjunction study of simulation and experiment is necessary for promoting the deep and systematic understanding of the phase behavior of BCPs under confinement, and sufficient attention should be paid to the studies of geometrical confinement on properties of the self-assembled polymeric materials.关键词：Block copolymers;Self-assembly;Confined space;Microphase separation;Interfacial properties
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发布时间：2021-01-26
Reviews
- 摘要：A new multi-functional aggregation-induced emission compound (TPECz) was synthesized by introducing carbazole groups to the tetraphenylethylene backbone through long alkyl chains. Its properties were investigated by UV-Visible absorption spectra (UV-Vis), photoluminescence spectroscopy (PL), thermogravimetric analyses (TG) and differential scanning calorimetry (DSC). It was found that the molecule emitted weakly in pure THF solution, but emittted strong fluorescence in their aggregated state, indicating that the TPECz was characterized as AIE-active. Meanwhile, the results demonstrated that the TPECz emitted strong blue fluorescence, and possessed good thermal stability with the fluorescence emission wavelength (λem=465 nm), decomposition temperature with 5% weight loss (Td) at 381℃ and glass transition temperature (Tg) at 58.7℃, respectively. It showed that TPECz can visually detect Fe3+ in H2O-THF mixed solvent (V/V=98/2) by quenching emission. The detection limit of Fe3+ in the mixed solvent can be down to 0.2 mmol/L for Fe3+ ion concentration. Moreover, the detection was of high sensitivity as the addition of other metal ions, including Mg2+, Al3+, Pb2+, Cr3+, Fe3+, Co2+, Ni2+ and Cu2+, did not induce obvious change on the solution fluorescence intensity. It indicated that TPECz was expected to work as an effective luminescent indicator for qualitative and quantitative detection of Fe3+ ions. Thanks to the electroactive moieties of the four peripheral carbazole units of TPECz, TPECz can be applied as a precursor to prepare the luminescent network film by electrochemical polymerization using a three-electrode cell with a Ti counter electrode, a Ag/Ag+ reference electrode, and a ITO glass working electrode. The resultant cross-linked film was characterized using scanning electron microscopy (SEM) and atomic force microscope (AFM). Moreover, it exhibits deep blue fluorescence with λem at 470 nm, so it is a potential material for fabrication of OLED devices. Therefore, TPECz can be used as a multi-functional luminophor.关键词：Tetraphenylethylene;Carbazole;Aggregation-induced emission;Electrochemical polymerization;Multi-functional luminophor
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发布时间：2021-01-26 -
Synthesis and Aggregation-enhanced Emission of Polymethacrylate with Pentaphenylpyrrole Side Group 增强出版
摘要：Methacrylate monomer M-PPP, which is aggregation-enhanced emission (AEE) active and with a conjugated pentaphenylpyrrole side group, was designed and synthesized through palladium-catalyzed cyclization of arylamine and diaryl acetylene, Suzuki cross-coupling and esterification with EDCI as dehydrant. A series of homopolymers P1, P2, P3 and copolymers CP41, CP21, CP11, CP12, CP14 were prepared by free radical polymerization of M-PPP and copolymerization of M-PPP with BMA. The molar ratio of M-PPP unit and BMA unit in copolymers CPs was calculated based on the chemical shift and integrations of their CH2 groups. The content of M-PPP units in the copolymers was lower than those in raw materials, mainly due to the low polymerization activity attributed to the bulky conjugated pentaphenylpyrrole side group. The monomer M-PPP, the polymers P1, P2, P3 and the copolymers CP41, CP21, CP11 were of high thermal stability with their decomposition temperature above 300℃, while the decomposition temperatures of CP12, CP14 decreased slightly because of the lower content of the conjugated pentaphenylpyrrole side group. Both the monomer M-PPP and the polymers exhibited obvious AEE feature in THF/H2O mixture. The fluorescence intensity of the polymers increased slowly when the water fraction (fw) was above 20%, and it increased faster when fw is above 80%. The relative fluorescence intensity (I/I0) reached to a maximum at fw of 95%, mainly attributed to the aggregation of the conjugated luminogen pentaphenylpyrrole segment in the side-chain and the entanglement of the flexible polymer main chains in THF/H2O mixture, which could restrict the motion of pentaphenylpyrrole and intramolecular rotation of the benzene rings, leading to enhanced fluorescence emission. The fluorescence intensity of M-PPP decreased a little when fw was lower than 70%, then increased sharply, and the maximal I/I0 was 3.9 at fw of 95%, which was higher than those of the polymers due to the lower content of conjugated pentaphenylpyrrole side group in the polymers. The copolymers CPs exhibited similar AEE behavior as the polymers P1, P2, P3 in THF/H2O mixture, and they showed better AEE feature when increasing the content of the conjugated pentaphenylpyrrole side group. Furthermore, the copolymers CPs could "turn-on" to detect lysine selectively in THF/H2O mixture due to the interaction of BMA unit and lysine, and more sensitive fluorescence response was observed for CP14 due to the higher BMA side-chain content, which is known to have stronger interaction with lysine.关键词：Aggregation-enhanced emission;Pentaphenylpyrroleside group;Polymethacrylate copolymer;Lysine fluorescence detecting- 36
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发布时间：2021-01-26 - 摘要：Two half-titanocenes, containing a phosphinimide ligand[(t-Bu)3P=N]CpTiCl2 (PT1) and[(t-Bu)3P=N]CpTiMe2 (PT2) as the main catalysts for olefin polymerization, were examined in propylene polymerization in the presence of methylaluminoxane (MAO) or[Ph3C] [B(C6F5)4] as the co-catalyst. The catalytic performance was also compared with typical {rac-[En(IndH4)2]ZrC12} (1), CpTiCl3 (2) and Cp2TiCl2 (3) catalysts. The effects of experimental conditions, including feeding molar ratio of the co-catalyst to the main catalyst[Al]/[Ti], temperature, propylene pressure and reaction time, on the catalytic activity of the polymerization, the molecular weight and molecular weight distribution of the resulting polypropylenes (PPs) were investigated in detail. A maximal activity of 3.25×106 g PP/molTi·h was attained using PT2/[Ph3C] [B(C6F5)4] in the presence of MAO at[Al]/[Ti]=800. Meanwhile, a highest molecular weight ofMw=4.42×105 with a molecular weight distribution of 1.73 was reached with PT1/MAO at[Al]/[Ti]=1200. The molecular weights were increased with decreased polymerization temperature, increased reaction pressure and polymerization time (tp). Interestingly, it was noted that an asymptotic plot of Mw versus tp was almost linear up to 15 min, indicating a "single-site" catalytic polymerization. 13C-NMR and IR analyses revealed that the resulting polymers were atactic PPs, which were more or less syndiotactically enriched atactic ones with higher diads r (62.28%) than m (37.72%). Furthermore, a calculated value of 1.04 for[mr/(2mm + mr)] +[mr/(2rr + mr)] indicated that the polymerization was conducted in agreement with the statistical model of Bernoullian. DSC measurements further confirmed the atactic microstructure of the PPs with a glass transition temperature (Tg) ranged from -3.7℃ to -2.6℃ without any melting endotherm. Accordingly, the PPs produced in this study by the phosphinimide catalysts were mainly made up of 1, 2-insertion units together with a small number of 2, 1-insertion units.关键词：Phosphine nitrogen ligand;Half-titanocene;Propylene polymerization;Sequence distribution
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发布时间：2021-01-26 - 摘要：Due to highly branched three-dimensional sphere-like molecular architecture, hyperbranched polymers have shown very different properties such as intramolecular cavities, low viscosity, high solubility and a large number of terminal functional groups if compared with their linear analogues. They can be facilely synthesized via a one-pot polymerization through different methods according to the type of monomers, including polycondensation of ABn monomers, self-condensing vinyl polymerization, self-condensing ring-opening polymerization and so on. Here, hyperbranched poly(ester amide)s (HBPEAs) with terminal carboxyl groups are prepared from benzene-1, 2, 4-tricarbonylic acid-1, 2-anhydride (BTAA) and ethanolamine (EMA) via two-step and one-step melt polycondensation, respectively. In two-step method, the anhydride group in BTAA first reacted with the amino group in EMA to form a AB2 intermediate with one hydroxyl groups and two carboxyl groups in ethanol according to the principle of non-equal reactivity of functional groups. After ethanol evaporated, the AB2 intermediate was melted at 220℃ to polymerize to produce HBPEA without gelation. Furthermore, HBPEA was also synthesized from BTAA and EMA at 220℃ through one-step melt polycondensation, more convenient in the industry. The resulting HBPEAs were characterized by 1H-NMR analysis, Ubbelohde viscometer, differential scanning calorimeter (DSC), thermo gravimetric analyzer (TGA) and refractive index measurements. their DBs are about 0.64 and intrinsic viscosities are about 0.120~0.146 dL/g. Their Tgs are about 125℃ and refraction indexes are about 1.57~1.58, which is similar to those of PC. The temperature of 5 wt% weight loss is above 350℃. Therefore, HBPEAs can be used as modification agent to process polycarbonate. When HBPEAs were added into PC or PC/CaCO3, not only the process ability of PC or PC/CaCO3 was improved, but also the colour of PC was kept unchanged. In addition, the mechanical properties and the surface roughness of PC or PC/CaCO3 were enhanced too. In summary, HBPEAs have very broad prospects for different applications.关键词：Hyperbranched poly (ester amide);Melt polycondensation;Rheological modification;Polycarbonate
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发布时间：2021-01-26 - 摘要：Kaolinite-urea intercalation complex was prepared using kaolinite as intercalation host and urea as intercalating agent. The kaolinite-urea intercalation complex was used as precursor to prepare exfoliated kaolinite by deintercalating urea molecules from the interlayers of kaolinite through ultrasonic treatment. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the as-prepared exfoliated kaolinite. A broad 001 diffraction of kaolinite with weak intensity showed the random orientation of kaolinite platelets. SEM micrograph confirmed the exfoliation of kaolinite particles with layer thickness of no more than 50 nm. The exfoliated kaolinite particles were used as filler to poly(ethylene-oxide)/LiClO4 (PEO/LiClO4) system to prepare PEO/kaolinite composites, with the aim to improve the ion conductivity and mechanical property of the PEO matrix. SEM, transmission electron microscopy (TEM), XRD and Fourier transform infrared spectroscopy (FTIR) were used to characterize the PEO/kaolinite composites. SEM and TEM micrographs exhibited a good dispersion of exfoliated kaolinite in PEO matrix. XRD results showed that the crystallinity of PEO was gradually decreasing with increased exfoliated kaolinite content. FTIR analysis indicated that the hydrogen bonding was formed between the oxygen atoms of PEO segments and the hydroxyl groups on kaolinite surface, and this interaction between PEO and kaolinite was beneficial to the decrease in crystallinity of PEO. In order to evaluate the effect of the exfoliated kaolinite on ion conductivity and mechanical property of PEO matrix, AC impedance measurement and mechanical test were carried out. The results indicated that the ion conductivity of the composites gradually increased with increased exfoliated kaolinite content and reached 6.0×10-5 S/cm at filler concentration of 20 wt%. The formation of amorphous region around the exfoliated kaolinite was beneficial for the Li+ ion conduction in PEO matrix. When the exfoliated kaolinite content reached 10 wt%, the formed amorphous regions were connected to each other to form a network for the transport of Li+ in the interconnected amorphous regions, leading to a sharp increase in ion conductivity. Moreover, the prepared composites under different drying temperature exhibited different ion conductivity. The reason was attributed to the change of PEO crystallinity with drying temperature, and the change trend of the ion conductivity was consistent with that of PEO crystallinity. Under the drying temperature of 95℃, the as-prepared composite possessed high ion conductivity (6.8×10-5 S/cm). In addition, the Young's modulus and tensile strength of the composites were improved because of the introduction of the exfoliated kaolinite into EPO matrix. The composites showed the maximal increase of 256% and 121% in Young's modulus and tensile strength, i.e., to 165.1 MPa and 6.743 MPa respectively, compared to PEO/LiClO4 (46.3 and 3.047 MPa). Therefore, the exfoliated kaolinite was a promising filler to prepare PEO based polymer electrolyte.关键词：Kaolinite;PEO;Ion conductivity;Mechanical property
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发布时间：2021-01-26 - 摘要：By carefully controlling the feeding ratio and slow feeding the reactants, 2-bromoisobutyryl end-capped tetraethylene glycol azobenzene-4, 4'-dicarboxylic ester (Br-EG4-AZO-EG4-Br, 1) was synthesized as an initiator. With n(γ-CD)/n(Br-EG4-AZO-EG4-Br)=4/1, the resulting initiator 1 was self-assembled with γ-cyclodextrin (γ-CD) in water to create first a double-chain stranded polypseudorotaxane (iPPR) as supramolecular initiator, which was then used to initiate, in situ, atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm) to prepare polypseudorotaxane containing block copolymers (PPRs). It was found that the added γ-CDs accommodate both an azobenzene and a folded tetraethylene glycol chain in the block copolymers, presented as a matched double-chain stranded inclusion complexing structure. However, in the case of self-assembling with PNIPAAm-EG4-AZO-EG4-PNIPAAm prepared from ATRP of NIPAAm, γ-CD was randomly distributed along the whole copolymer chain to give access to a series of loose-fit single-chain stranded inclusion complexing structured polypseudorotaxanes (aPPRs). Compared with Br-EG4-AZO-EG4-Br and aPPRs, the characteristic peak of ultraviolet (UV) absorption due to trans-azobenzene in PPRs was obviously red-shifted, but the unique cis-isomerization of this group appeared not leading to the threaded γ-CDs sliding off the polymeric chain. All these characterizations suggested that the matched double chain stranded inclusion complexing structure was constructed by an azobenzene and a folded tetraethylene glycol chain jointing to enter the cavity of γ-CD, showing not only a relatively higher stability, but also a reversible transformation into the double tetraethylene glycol chain stranded inclusion complexing structure in the process of cis-isomerization of the azobenzene.关键词：Azobenzene;Block copolymer;γ-CD;Double-chain stranded inclusion complexing structure;Polypseudorotaxane
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发布时间：2021-01-26 - 摘要：A new strategy was proposed to improve foaming properties of poly(butylene succinate) (PBS) via blending it with low content of poly(lactic acid) (PLA). Biodegradable PBS/PLA blend samples with PLA content of 7 wt%, 15 wt% and 20 wt% and pure PBS sample were prepared using a single-screw extruder with a chaotic mixing screw developed in our group. The samples were then foamed using supercritical carbon dioxide as physical foaming agent in a batch process. The cellular structure of the foamed samples was investigated, and its formation mechanism was analyzed. At foaming temperature (Tf) of 120℃, the foamed PBS sample exhibited an irregular cellular structure and wider cell diameter distribution (5-30 μm). Adding low PLA content (7 wt%, 15 wt% or 20 wt%) obviously improved the foaming properties of the PBS. Microcells were developed with more uniform distribution, more regular shape, and smaller diameter (with a mean value of about 10 μm) for all the foamed blend samples. This is attributed to improved storage modulus, complex viscosity and especially melt strength of the PBS induced by added PLA. Moreover, the cell diameters for the foamed blend samples exhibited a much narrower distribution (4-18 μm) and followed Gaussian distribution, resulting from good dispersion of the PLA microdomains. Further, the effect of theTf on the cellular structure of microcellular samples of the PBS and the blend with 15 wt% of PLA was investigated. As for the PBS, the lower Tf limit for foaming was dictated by its higher crystallinity degree, whereas the upper one by its low melt strength. Specifically, the lower Tf limit was 115℃. When lowering the Tf to 110℃, only a few sparse cells appeared in the foamed PBS sample, which was inferred to be developed at the core of spherulite. Raising the Tf to 120 or 125℃, the wall of some cells was ruptured. Adding 15 wt% of PLA shifted the lower Tf limit of the PBS from 115℃ to 110℃, and obviously improved the cellular structure uniformity and decreased the cell diameters for the foamed samples prepared at relatively high Tfs (120 and 125℃).关键词：PBS/PLA blend;Melt blending;Supercritical carbon dioxide foaming;Cellular structure;Rheological properties;Melt strength
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发布时间：2021-01-26 - 摘要：Melt-branching of high density polyethylene (HDPE), through free radical reaction, was carried out in the presence of dicumyl peroxide (DCP) as the initiator, neopentyl glycol diacrylate (NPGDA) as difunctional monomer, and zinc dimethyldithiocarbamate (ZDMC) as the free radical concentration regulator. Results showed that HDPE with long branching chains and low gel content was obtained under optimized reaction time, which was corresponding to the reaction peak-the second peak in the torque curve. After this melt branching reaction, the molecular weight of the modified HDPE increased slightly and its molecular weight distribution became wider compared with the virgin linear HDPE. The branching degree of modified HDPE increased with increased monomer content, with a more apparent shear thinning in the complex viscosity versus frequency (η*-ω) plots. The regularity of the polyethylene molecule was broken up after the long branching chains being introduced, which decreased the degree of crystallinity in the modified polyethylene. While the crystallization onset temperature improved and the size of spherocrystal obviously decreased with the nucleation of the long branching chains in the modified HDPE, a threshold value for the branching was shown to exist by the environmental stress cracking resistance test on the modified polyethylene. When monomer content exceeded 0.6 phr, the molecule shape of the long chain branched polyethylene transformed from asymmetric star-like to comb-like, which made the environmental stress cracking resistance time be larger than 1000 h, the strength, the modulus and the impact toughness were all enhanced at the same time. However, the branching degree was reduced with an overlong time mixing and melt-branching reaction, the comb-like branching chains were not formed by consequence, which made an inapparent enhancement for the environmental stress cracking resistance performance of the modified polyethylene.关键词：High density polyethylene;Long chain branching;Crystallization;Environmental stress cracking resistance;Mechanical property
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发布时间：2021-01-26 - 摘要：The C=C double bonds in the main chain of hydroxyl-terminated polybutadiene (DHTPB), obtained by the degradation of polybutadiene rubber, were partially epoxided using m-chloroperoxybenzoic acid (mCPBA) as epoxidation reagent. A series of epoxided HTPBs (EHTPB) with different epoxy contents (5%, 10% and 15%) were prepared by tuning the molar ratio of mCPBA to C=C double bonds. The structures of EHTPBs were characterized by Fourier transform-infrared (FTIR), nuclear magnetic resonance (1H-NMR) spectroscopy and gel permeation chromatography (GPC). The epoxy percent in EHTPBs from 1H-NMR spectra was in accordance with the design. In addition, a series of EHTPB-based polyurethane elastomers (EPU) were prepared by the reaction between EHTPB and 4, 4'-diphenylmethane diisocyanate with 1, 4-butanediol as a chain extender. Mechanical and thermal properties of the EPU samples were characterized by tensile test, differential scanning calorimetry (DSC) and thermal gravity analysis (TGA). With increased epoxy percent in EHTPB, the Young's modulus and the tensile strength of the EPU samples increased, whereas the elongation at break decreased. The sample EPU10 prepared with 10% of epoxy had the best mechanical properties with 8.82 MPa as Young's modulus, 7.83 MPa as tensile strength, and (485 ±23)% as elongation at break. The elasticity recovery of the EPU sample was slightly better than HTPB-based PU (EPU0). The results with TGA test showed that the thermal degradation of EPU, similar to EPU0, was divided into three stages. However, the EPU samples had better thermal stability with the initial degradation temperature at 210℃, about 30℃ higher than that of EPU0. The DSC results showed that the glass transition temperature (Tg) of EPU gradually increased as epoxy percent was increased, though still lower than that of HTPB (FHTPB) based PUs prepared by free-radical polymerization.关键词：Polyurethane elastomer;Hydroxyl-terminated polybutadiene;Epoxidation;Mechanical properties;Thermal properties
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发布时间：2021-01-26 - 摘要：An novel phosphaphenanthrene derivative, 6H-dibenzo[c, e] [1, 2]oxaphosphinine-6-sulfide (DOPS), was synthesized through the reaction of DOPO and phosphorus pentasulfide (P2S5). The structure of the synthesized compound was characterized and investigated by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), hot stage melting point determination, and elemental analysis. This flame retardant was aimed at improving the flame retardancy of EP. The intumescent flame retardant (IFR), composed of DOPS and ammonium polyphosphate (APP) at DOPS/APP ratio of 1:2, was added into EP to form a series of epoxy resin (FR-EP) modified by the flame retardants. The thermal stability was studied by thermal gravimetric analysis (TGA). Flame retardant properties as well as burning behavior of the epoxy resin composites were investigated by limited oxygen index (LOI) and vertical burning test (UL-94). Fire properties of the modified epoxy resin were tested by cone calorimeter. The morphological characteristics of the char residue after cone test were studied by scanning electron microscopy (SEM). DOPS/APP flame retardant increased not only the UL-94 grade but also the LOI value. It was also found that the EP modified by IFR still past UL94 V-0 rating, and its limited oxygen index value reached 29.2% when the flame retardant content was 30 wt%. TGA data indicated that the amount of the char residue at 700℃ was 49.33%. The cone experimental results showed that the values of av-HRR, pk-HRR, and av-EHC of the IFR-EP were lowered to 70%, 79%, and 60% of those in the original EP, respectively. When the amount of DOPS was increased to 30 wt%, a high LOI value of 27.6% was obtained, the DOPS-modified EP could still pass UL94 V-0 rating. A series of comprehensive tests showed that DOPS/APP was effective flame retardant on epoxy resin and the flame retardant effect of the compound flame retardant was better than that of the single flame retardant. TGA, DTG, CONE, SEM comprehensive analysis revealed that epoxy resin modified by DOPS/APP was more thermo-stable compared to the pure epoxy. Filled with flame retardant, DOPS/APP-EP formed the continuous, intact and porous foam char layers after burning test. By covering the surface of the polymer, char layer prevented mass and heat exchange from circumstance.关键词：6H-dibenzo[c, e][1, 2]oxaphosphinine-6-sulfide;Synthesis;Flame retardant properties
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发布时间：2021-01-26 - 摘要：Blending type of ABS with different polybutadiene rubber (PB) and polyacrylonitrile (AN) contents in SAN phase is prepared at 240℃ to study the effects of PB and AN content on the structure and the properties of DB/ABS blends. Different kinds of productive ABS along with the blend-type ABS are used to compare the properties of PC/ABS and DB/ABS blends comprehensively. All blends are made by melt blending for 10 min with sheer rate of 30 r/min. The result shows that, in DB/Blend-type ABS (70/30) blends, PB content exhibits significant influence on the tensile properties. Samples with 6.3 wt% of PB always show the best performance both in yield strength and elongation at break when AN content is fixed at 18 wt%, 25 wt% and 30 wt%; while increasing AN content in the sample with the same PB content would result in better blends properties even not so obvious as PB content. Scanning electron microscopy gives exactly the same trend for phase morphology with PB and AN contents, revealing best uniform scale of dispersed phase (ABS) among 0.5-1.2 μm at 6.3 wt% of PB. Thermal gravimetric analysis shows that all DB/ABS blends have good thermal stability, which is not obviously affected by PB content and AN content. Single peak of glass transition shows good compatibility in the DB/ABS blends. Excellent compatibility of DB with ABS in the sample is exhibited through dynamic mechanical analysis. The glasstransition temperature of DB/ABS blends are closed to that of DB, mildly affected by PB and AN content. Besides, both blending type ABS and different kinds of productive type ABS are used to compare the properties of DB/ABS blends and traditional bisphenol-A-type PC/ABS blends. Basic laws of tensile properties in DB/ABS remain the same as in PC/ABS blends using different types of ABS.关键词：Isosorbide-type polycarbonate;ABS resin;AN content;PB content;Structure and property
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发布时间：2021-01-26 - 摘要：The effects of different natural environment on rigid PVC natural aging were studied in detail. Rigid PVC samples were placed in Sinkiang Ruoqiang country and Hainan Qionghai city of China, respectively, for natural aging. Then, color and corresponding molecular structure changes of the natural aged PVC were investigated by chromatic aberration, FTIR and UV methods. In particular, monthly solar radiation in Ruoqiang is 508.25 MJ/m2, which is higher than that of Qionghai. But average temperature, medial humidity, monthly total precipitation and oxygen pressure in Ruoqiang are far lower than those in Qionghai. As a result, color change and molecular structure change of the rigid PVC samples aged in the two places were different. It was found that brightness (△L) of PVC surface decreased with increase of aging time. However, redness (△a), yellowness (△b) and color difference (△E) increased with increase of aging time. In addition, redness (△a), yellowness (△b) and color difference (△E) of the PVC aged in Ruoqiang were larger than those in Qionghai. Meanwhile, surface color change was accompanied by molecular structure change. Firstly, FTIR results showed that C=C and C=O were formed and they increased with the aging time, which indicated that dehydrochlorination and oxidation reactions took place. And when aged in Ruoqiang, the amount of C=C was larger than C=O, indicating that dehydrochlorination played a dominant role. When aged in Qionghai, the amount of C=C was similar to that of C=O, indicating that dehydrochlorination was at a similar reaction speed with oxidation. Secondly, UV results confirmed that C=C long conjugated sequence (conjugation length ≥ 8) of PVC increased with aging time. In addition, the amounts of C=C, C=O and C=C long conjugated sequence (conjugation length ≥ 8) of PVC aged in Ruoqiang were larger than those in Qionghai. Thirdly, it was also found that there was a good correlation between the color change and the C=C long conjugated sequence (conjugation length ≥ 8), but C=O groups contributed little to color change. Finally, it was concluded that solar radiation was the main environmental factor that affected natural aging of rigid PVC. Based on this, rigid PVC materials underwent more remarkable color change and molecular structure change when aged in Ruoqiang.关键词：Rigid PVC;Natural aging;Solar radiation;Color change;C=C long conjugated sequence
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发布时间：2021-01-26 - 摘要：Ballistic gelatin has been adopted as a standard target block for experimental studies on the end effect of bullets and fragments. Therefore, its structural stability, that is, the aging behavior will affect the evaluation results considerably. In this work, the aging behavior of 10 wt% ballistic gelatin is studied by using the rheological small-strain-oscillatory experiment. For the cooling stage from the melting temperature (the sol-gel point) to a target temperature, the aging mechanism is generally complicated by uneven and unstable temperature field. Since the gelatin specimen is thin, we can neglect the uneven and unstable temperature field and have established a linear dependence of the elastic modulus on the cooling rate via various experimental cooling rates. This is to provide estimations for the initial elastic modulus needed in the later isothermal-aging model. The isothermal-aging behavior shows that the elastic-modulus-time curves of the ballistic gelatin are self-similar in shape for different temperatures. For fixed aging time, it is found that the elastic modulus decreases linearly with the aging temperature and intersects near the sol-gel point of the ballistic gelatin, 301 K. Inspired by the second-order reaction kinetics model, proposed by Normand et al., an aging rate constant, k, is introduced and a model to predict the elastic modulus for the early stage (less than 20 h) of isothermal aging is constructed:G'(t, T)=G'0(T) + G'a(T)kt/(1 + kt). In this model, the modulus-temperature lines are linear at the initial, G'0(T), and the (assumed) infinite aging time, G'∞ (T). And these lines intersect around the sol-gel point. The relationship between the aging-rate constant and the degree of undercooling, △T, can be well described by the Flory-Weaver equation. The relative error between the prediction of the second-order reaction kinetics model and the experimental values are less than 10%. In addition, the modulus-temperature curves for various fixed aging time, calculated by the model, indeed show approximately linear behavior. A dimensionless master curve is constructed by normalizing the elastic modulus and the aging time for different aging temperatures. This result indicates that the variation of temperature just changes the time scale factor, that is, it alters the aging-rate constant. The second-order kinetics model developed in this paper provides a pragmatic tool to predict the aging moduli of 10 wt% gelatin in ballistic experiments.关键词：Ballistic gelatin;Cooling model;Isothermal aging;Second-order reaction kinetics;Aging rate constant
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发布时间：2021-01-26
Research Article
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