Subjects -> MANUFACTURING AND TECHNOLOGY (Total: 362 journals)
    - CERAMICS, GLASS AND POTTERY (31 journals)
    - MACHINERY (34 journals)
    - MANUFACTURING AND TECHNOLOGY (223 journals)
    - METROLOGY AND STANDARDIZATION (5 journals)
    - PACKAGING (19 journals)
    - PAINTS AND PROTECTIVE COATINGS (4 journals)
    - PLASTICS (42 journals)
    - RUBBER (4 journals)

PLASTICS (42 journals)

Showing 1 - 32 of 32 Journals sorted alphabetically
ACS Applied Polymer Materials     Hybrid Journal   (Followers: 9)
Acta Polymerica     Hybrid Journal   (Followers: 9)
Additives for Polymers     Full-text available via subscription   (Followers: 20)
Advanced Industrial and Engineering Polymer Research     Open Access   (Followers: 4)
Advances in Polymer Technology     Open Access   (Followers: 13)
Chinese Journal of Polymer Science     Hybrid Journal   (Followers: 9)
Cirugia Plastica Ibero-Latinoamericana     Open Access  
European Polymer Journal     Hybrid Journal   (Followers: 44)
International Journal of Biobased Plastics     Open Access   (Followers: 2)
International Journal of Polymeric Materials     Hybrid Journal   (Followers: 6)
International Polymer Processing     Full-text available via subscription   (Followers: 1)
Iranian Journal of Polymer Science and Technology     Open Access   (Followers: 1)
Journal of Applied Polymer Science     Hybrid Journal   (Followers: 115)
Journal of Inorganic and Organometallic Polymers and Materials     Hybrid Journal   (Followers: 8)
Journal of Polymer Research     Hybrid Journal   (Followers: 7)
Journal of Polymer Science Part C : Polymer Letters     Hybrid Journal   (Followers: 5)
Journal of Polymers and the Environment     Hybrid Journal   (Followers: 1)
Majalah Kulit, Karet, dan Plastik     Open Access  
Microplastics and Nanoplastics     Open Access  
Plastic and Polymer Technology     Open Access   (Followers: 40)
Plastic and Reconstructive Surgery     Hybrid Journal   (Followers: 30)
Plastics Engineering     Partially Free  
Polymer     Hybrid Journal   (Followers: 86)
Polymer Bulletin     Hybrid Journal   (Followers: 7)
Polymer Engineering & Science     Hybrid Journal   (Followers: 15)
Polymer Science Series B     Hybrid Journal   (Followers: 4)
Polymer Science Series C     Hybrid Journal   (Followers: 3)
Polymer Science Series D     Hybrid Journal   (Followers: 3)
Polymer Science, Series A     Hybrid Journal   (Followers: 3)
Polymer-Plastics Technology and Materials     Hybrid Journal   (Followers: 5)
Reinforced Plastics     Full-text available via subscription   (Followers: 17)
SPE Polymers     Open Access  
Similar Journals
Journal Cover
Chinese Journal of Polymer Science
Journal Prestige (SJR): 0.506
Citation Impact (citeScore): 2
Number of Followers: 9  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0256-7679 - ISSN (Online) 1439-6203
Published by Springer-Verlag Homepage  [2469 journals]
  • Liquid Crystalline Polymers

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      PubDate: 2022-02-01
       
  • Benzobisthiazole Polymer with Resonance-assisted Hydrogen Bonds for
           High-performance Transistor and Solar Cell Applications

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      Abstract: Benzobisthiazole polymer with resonance-assisted hydrogen bonds (RAHBs) has been synthesized for both organic field-effect transistor and polymer solar cell applications. The properties of the hydrogen bonded polymer are compared with the reference polymer without RAHBs. Single-crystal X-ray diffraction analyses of the building block reveal that the RAHB interactions are formed between the carbamate hydrogen and imine nitrogen of the thiazoles. The hydrogen donor and acceptor are connected by π-conjugated molecular framework and the hydrogen-bridged quasi aromatic rings lock the conformation of the building block. The building block adopted a layered sandwich packing in crystal instead of slipped herringbone stacking which was often found in the crystal of benzobisthiazole derivatives. The polymer PCBTZ-TT with RAHBs showed deeper HOMO/LUMO energy level (about 0.2 eV) than reference polymer. The PCBTZ-TT demonstrated the hole mobility of 0.96 cm2·V−1·s−1 in field-effect transistor devices and achieved power conversion efficiency of 13.6% in solar cell devices with Y6 as acceptor without any additive.
      PubDate: 2022-02-01
       
  • The Influence of Peroxide on Bubble Stability and Rheological Properties
           of Biobased Poly(lactic acid)/Natural Rubber Blown Films

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      Abstract: This study investigated the effects of natural rubber (NR) and an organic peroxide on the rheological properties, mechanical properties, morphology, and bubble stability during film blowing of poly(lactic acid) (PLA). The NR and peroxide contents were varied from 0 wt% to 25 wt% and 0 wt% to 0.5 wt%, respectively. The results confirmed that the presence of well-dispersed NR could significantly improve the toughness, elongation at break, and processability of PLA films, where the optimal amount of NR was 15 wt%. For the reactive blending with peroxide, a suitable peroxide content for good film toughness and clarity was 0.03 wt%, while the higher content of 0.1 wt% could provide slightly higher processability. These contents are considered much lower than that in the PLA system (without NR), which required up to 0.5 wt% peroxide. The rheological studies indicated that the melt strength, the storage modulus (G′) and complex viscosity (η′) at low frequency could be correlated with good film blowing processability of the PLA/NR films at low gel contents. These parameters failed to correlate in the films having high gel contents as the deformation rate experienced by each test was different leading to the different levels of response to the type and amount of gels.
      PubDate: 2022-02-01
       
  • Software Package: An Advanced Theoretical Tool for Inhomogeneous Fluids
           (Atif)

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      Abstract: In spite of the impending flattening of Moore’s law, the complexity and size of the systems we are interested in keep on increasing. This challenges the computer simulation tools due to the expensive computational cost. Fortunately, advanced theoretical methods can be considered as alternatives to accurately and efficiently capture the structural and thermodynamic properties of complex inhomogeneous fluids. In the last decades, classical density functional theory (cDFT) has proven to be a sophisticated, robust, and efficient approach for studying complex inhomogeneous fluids. In this work, we present a pedagogical introduction to a broadly accessible open-source density functional theory software package named “an advanced theoretical tool for inhomogeneous fluids” (Atif) and of the underlying theory. To demonstrate Atif, we take three cases as examples using a typical laptop computer: (i) electric double-layer of asymmetric electrolytes; (ii) adsorptions of sequence-defined semiflexible polyelectrolytes on an oppositely charged surface; and (iii) interactions between surfaces mediated by polyelectrolytes. We believe that this pedagogical introduction will lower the barrier to entry to the use of Atif by experimental as well as theoretical groups. A companion website, which provides all of the relevant sources including codes and examples, is attached.
      PubDate: 2022-02-01
       
  • UV-Vis-NIR Light-deformable Shape-memory Polyurethane Doped with
           Liquid-crystal Mixture and GO towards Biomimetic Applications

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      Abstract: Nature has been inspiring material researchers to fabricate biomimetic functional devices for various applications, and shape-memory polymer materials (SMPMs) have received tremendous attention since the promising intelligent materials possess more advantages over others for the fabrication of biomimetic functional devices. As is well-known, SMPMs can be stimulated by heat, electricity, magnetism, pH, solvent and light. From the viewpoint of practical applications, ultraviolet (UV)-visible (Vis)-near infrared (NIR) light-responsive SMPMs are undoubtedly more advantageous. However, up to now, UV-Vis-NIR light-deformable SMPMs by combining photothermal and photochemical effects are still rarely reported. Here we designed a UV-Vis-NIR light-deformable SMP composite film via incorporating a liquid crystal (LC) mixture and graphene oxide (GO) into a shape-memory polyurethane matrix. The elongated composite films exhibited interesting photomechanical bending deformations with different light-triggered mechanisms, (1) photochemically induced LC phase transition upon UV exposure, (2) photochemically and photothermally induced LC phase transition upon visible-light irradiation, (3) photothermally triggered LC phase transition and partial stress relaxation upon low-intensity NIR exposure. All the deformed objects could recover to their original shapes by high-intensity NIR irradiation. Moreover, the biomimetic circadian rhythms of acacia leaves and the biomimetic bending/spreading of fingers were successfully achieved, which could blaze a way in the field of biomimetic functional devices due to the excellent light-deformable and shape-memory properties of the SMP composite films.
      PubDate: 2022-02-01
       
  • Preheat Compression Molding for Polyetherketoneketone: Effect of Molecular
           Mobility

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      Abstract: Polyetherketoneketone (PEKK) is a new evolving polymeric material, and is considered as another important member of the polyaryletherketone (PAEK) family in addition to polyetheretherketone (PEEK). Hot compression molding can be used to compact and consolidate the PEKK products, where the temperature and pressure play key roles to affect the molecular mobility, entanglement and crystallization, and thus the mechanical properties of PEKKs. In this study, a preheating treatment was introduced in the compression molding, and it is found that such preheating is very essential to avoid the formation of crystal Form II, based on the increased chain entanglement. Molecular dynamics simulations revealed that the molecular mobility is always suppressed when a compression is applied. Therefore, by increasing the entanglement via the preheating and maintaining such entanglement in the consequent compression molding, strong and tough PEKK materials were obtained, with a negligible fraction of crystal Form II.
      PubDate: 2022-02-01
       
  • Polymer Vesicles with Upper Critical Solution Temperature for
           Near-infrared Light-triggered Transdermal Delivery of Metformin in
           Diabetic Rats

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      Abstract: Near-infrared light (NIR) triggered transdermal drug delivery systems are of great interest due to their on-demand drug release, which enable to enhance drug treatment efficiency as well as reduce side effect. Herein, a NIR-triggered microneedle (MN) patch array has been fabricated through depositing the photothermal conversion agent and anti-diabetic drug-loaded polymer vesicles with upper critical solution temperature (UCST) into dissolvable polymer matrix. The UCST-type polymer has a clearing point temperature of 41 °C and the drug-loaded polymer vesicles present excellent NIR-triggered and temperature responsive drug release behavior in vitro due to the disassociation of polymer vesicles upon NIR irradiation. After applying MNs to diabetic rats, significant hypoglycemic effect is achieved upon interval NIR irradiation and the blood glucose concentration can decrease to normal state for several hours, which enables to achieve the goal of on-demand drug release. This work suggests that the NIR-triggered MN drug release device has a potential application in the treatment of diabetes, especially for those requiring an active drug release manner.
      PubDate: 2022-02-01
       
  • Synthesis of Thieno[3,4-b]pyrazine-based Alternating Conjugated Polymers
           via Direct Arylation for Near-infrared OLED Applications

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      Abstract: Three alternating conjugated polymers, namely PFTP, PCzTP, and PSiTP, which combine a thieno[3,4-b]pyrazine (TP) unit with different benzene-based donor units such as 9,9-dioctylfluorene, 9-heptadecyl-9H-carbazole and 5,5-dioctyl-5H-dibenzo[b,d]silole, were synthesized in good yield (>85%) and high molecular weight up to Mn=5.82×104via direct arylation polymerization (DArP). All the resultant polymers exhibit moderate bandgap of about 1.80 eV and strong deep red/near-infrared emitting in the solid state. Among them, the PSiTP-based electroluminescence (EL) devices with an architecture of ITO/PEDOT:PSS/PTAA/emitting layer/TPBi/LiF/Al give the best performance with a maximum luminance of 2543 cd/m2 at 478 mA/cm2. This work expands the application scope of high-performance conjugated polymers which can be synthesized by DArP.
      PubDate: 2022-02-01
       
  • Biodegradable Foaming Material of Poly(butylene adipate-co-terephthalate)
           (PBAT)/Poly(propylene carbonate) (PPC)

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      Abstract: A biodegradable blend foaming material of poly(butylene adipate-co-terephthalate) (PBAT)/poly(propylene carbonate) (PPC) was successfully prepared by chemical foaming agent and screw extrusion method. First, PBAT was modified by bis(tert-butyl dioxy isopropyl) benzene (BIBP) for chain extension, and then the extended PBAT (E-PBAT) was foamed with PPC using a twin (single) screw extruder. By analyzing the properties of the blends, we found that Young’s modulus increased from 58.8 MPa of E-PBAT to 244.7 MPa of E-PBAT/PPC 50/50. The viscosity of the polymer has a critical influence on the formation of cells. Compared with neat PBAT (N-PBAT), the viscosity of E-PBAT increased by 3396 Pa·s and E-PBAT/PPC 50/50 increased by 8836 Pa·s. Meanwhile, the dynamic mechanical analysis (DMA) results showed that the storage modulus (E′) at room temperature increased from 538 MPa to 1650 MPa. The various phase morphologies (“sea-island”, “quasi-co-continuous” and “co-continuous”) and crystallinity of the blends affected the spread velocity of gas and further affected the foaming morphology in E-PBAT/PPC foam. Therefore, through the analysis of phase morphology and foaming mechanism, we concluded that the E-PBAT/PPC 70/30 component has both excellent strength and the best foaming performance.
      PubDate: 2022-02-01
       
  • Surface and Interface Engineering for Advanced Nanofiltration Membranes

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      Abstract: Nanofiltration has been attracting great attention in alleviating the global water crisis because of its high efficiency, mild operation, and strong adaptability. Over decades, it remains a challenge to break the upper limit of performance and establish the formation-structure-property relationship for nanofiltration membranes. This feature article summarizes our recent progress in the preparation of high-performance thin-film composite (TFC) nanofiltration membranes, focusing on the mussel-inspired deposition method and the optimized interfacial polymerization (IP). By accelerating the oxidation of polydopamine and equilibrating the rate of aggregation and deposition processes, the mussel-inspired deposition method realizes the rapid and uniform formation of selective coatings or nanofilms. Diverse deposition systems endow the selective layer with rich chemical structures and easy post-functionalization, highlighting its potential in water treatment. As for optimizing the conventional IP, the rapid polycondensation of amine and acid chloride groups is slowed down to enable the controllability of IP at the water-organic interface. The homogeneity and integrity of the TFC membranes are improved by constructing a uniform reaction platform and introducing a viscous medium to control the amine diffusion, which facilitates the water permeability and promotes the separation efficiency. We have proposed a series of practical strategies for improving TFC membranes and might provide more inspiration for other nanofiltration techniques.
      PubDate: 2022-02-01
       
  • Block Copolymer Networks Composed of Poly(ε-caprolactone) and
           Polyethylene with Triple Shape Memory Properties

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      Abstract: In this contribution, we reported a novel synthesis of block copolymer networks composed of poly(ε-caprolactone) (PCL) and polyethylene (PE) via the co-hydrolysis and condensation of α, ω)-ditriethoxylsilane-terminated PCL and PE telechelics. First, α, ω)-dihydroxyl-terminated PCL and PE telechelics were synthesized via the ring-opening polymerization of ε-caprolactone and the ring-opening metathesis polymerization of cyclooctene followed by hydrogenation of polycyclooctene. Both α, ω)-ditriethoxylsilane-terminated PCL and PE telechelics were obtained via in situ reaction of α, ω-dihydroxyl-terminated PCL and PE telechelics with 3-isocyanatopropyltriethoxysilane. The formation of networks was evidenced by the solubility and rheological tests. It was found that the block copolymer networks were microphase-separated. The PCL and PE blocks still preserved the crystallinity. Owing to the formation of crosslinked networks, the materials displayed shape memory properties. More importantly, the combination of PCL with PE resulted that the block copolymer networks had the triple shape memory properties, which can be triggered with the melting and crystallization of PCL and PE blocks. The results reported in this work demonstrated that triple shape memory polymers could be prepared via the formation of block copolymer networks.
      PubDate: 2022-02-01
       
  • Preparation of High-performance Polyimide Fibers with Wholly Rigid
           Structures Containing Benzobisoxazole Moieties

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      Abstract: In this work, a fully rigid coplanar symmetric heterocyclic unit was introduced into the rigid polyimide macromolecular backbone structure to prepare high-performance polyimide fibers. The novel co-polyimide (co-PI) fibers based on 3,3′,4,4′-biphenyltetracarboxylic anhydride (BPDA), p-phenylenediamine (PDA) and 2,6-(4,4′-diaminodiphenyl) benzo[1,2-d:5,4-d′] bisoxazole (PBOA) were fabricated via a two-step wet-spinning method. The effects of benzobisoxazole moiety on spinnability, aggregation structure, and mechanical properties of fibers were systematically discussed. The detailed structural analysis revealed that the well-defined aggregation structures of co-PI fibers were obtained from initial amorphous structure when post hot-drawing temperature was higher than 460 °C under proper drawing ratio, and the incorporation PBOA into BPDA-PDA structures produced more compact structural co-PI fiber than homo BPDA-PDA fiber. The BPDA-PDA/PBOA co-PI fibers exhibited optimum tensile strength and modulus of 2.65 and 103 GPa, which increased by 182% and 84% compared to the homo BPDA-PDA fiber, respectively.
      PubDate: 2022-01-12
       
  • Thermally Conductive Poly(lactic acid) Composites with Superior
           Electromagnetic Shielding Performances via 3D Printing Technology

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      Abstract: This work proposes a facile fabrication strategy for thermally conductive graphite nanosheets/poly(lactic acid) sheets with ordered GNPs (o-GNPs/PLA) via fused deposition modeling (FDM) 3D printing technology. Further combinations of o-GNPs/PLA with Ti3C2Tx films prepared by vacuum-assisted filtration were carried out by “layer-by-layer stacking-hot pressing” to be the thermally conductive Ti3C2Tx/(o-GNPs/PLA) composites with superior electromagnetic interference shielding effectiveness (EMI SE). When the content of GNPs was 18.60 wt% and 4 layers of Ti3C2Tx (6.98 wt%) films were embedded, the in-plane thermal conductivity coefficient (λ∥) and EMI SE (EMI SE∥) values of the thermally conductive Ti3C2Tx/(o-GNPs/PLA) composites significantly increased to 3.44 W·m−1·K−1 and 65 dB (3.00 mm), increased by 1223.1% and 2066.7%, respectively, compared with λ∥ (0.26 W·m−1·K−1) and EMI SE∥ (3 dB) of neat PLA matrix. This work offers a novel and easily route for designing and manufacturing highly thermally conductive polymer composites with superior EMI SE for broader application.
      PubDate: 2022-01-12
       
  • Enhancement on Hemilabile Phosphine-Amide Palladium and Nickel Catalysts
           for Ethylene (Co)Polymerization with Polar Monomers Using a Cyclizing
           Strategy

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      Abstract: To address the issue of hemilabile catalyst in olefin polymerization catalysis, a cyclizing strategy was used to construct novel N-bridged phosphine-carbonyl palladium and nickel catalysts, resulting in improvements on ethylene (co)polymerizations. The N-bridged phosphine-carbonyl Pd catalysts (Pd1–Pd5) and Ni catalysts (Ni1–Ni5) bearing five- to eight-membered-ring structures were designed and synthesized. Catalytic performance for ethylene (co)polymerization became better as the size of N-containing bridge increased. The seven-membered-ring bridged catalysts Pd4 and Ni4 exhibited the best performance in terms of catalytic activity, polymer molecular weight and incorporation of acrylates and acrylic acid. The better performance of these catalysts bearing larger-size bridges was tentatively attributed to the methylene-induced higher electron density around nitrogen, which strenghtens the coordination of carbonyl group to metal center, and also to the steric effect offered by this cyclization. This work provides a new strategy to enhance hemilabile polymerization catalysts.
      PubDate: 2022-01-11
       
  • A Furan-based Phosphaphenanthrene-containing Derivative as a Highly
           Efficient Flame-retardant Agent for Epoxy Thermosets without Deteriorating
           Thermomechanical Performances

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      Abstract: In order to reduce greenhouse gas emissions, developing flame retardants from bio-based resources has aroused extensive interest in recent years. In this work, we utilized furfural (biomass) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to synthesize a bio-based co-curing agent (FGD) to combine with 4,4′-diaminodiphenyl methane (DDM) for obtaining a low-phosphorus loading flame-retardant epoxy thermosets. The introduction of FGD decreased the activation energy of the curing progress, enhanced the mechanical properties of the epoxy thermosets, and did not affect the glass transition temperature of the epoxy thermosets. EP-5.0 had a lower thermal degradation rate and a doubled char yield compared with EP-0. The phosphorus content of EP-5.0 was only 0.45 wt%, while EP-5.0 reached the UL-94 V-0 rating with a high LOI value of 32%. Compared with EP-0, the PHRR of EP-2.5 and EP-5.0 decreased by 22.3% and 31.3%, respectively. The SEM results showed that the addition of FGD made the char residues more uniform and denser, which could effectively prevent combustible volatiles from escaping from the degradation area to the flame area and isolate the heat transfer so that the epoxy thermosets had an excellent flame-retardant performance.
      PubDate: 2022-01-11
       
  • Stress-induced Solid-Solid Crystal Transition in Trans-1,4-polyisoprene

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      Abstract: The polymorphic transition of trans-1,4-polyisoprene (TPI) during stretching was investigated by in situ wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The influences of the initial structure, stretching temperature, and strain rate on the contents of different crystal modifications (α, β) were explored. The results confirm that the α-β transition occurs during stretching of TPI that only contains α crystal (α-TPI). When the stress is relaxed, the β crystal formed during stretching remains, which indicates that the transition is irreversible. On the other hand, stretching of TPI that only contains β crystal (β-TPI) results in orientated β crystal. No β-α transition occurs during stretching. The different structures of stretched α-TPI and β-TPI exclude the previously proposed “melting-recrystallization mechanism”. The α-β transition depends significantly on temperature and strain rate, indicating the transition is governed both by thermodynamics and kinetics. Our results support a solid-solid transition mechanism rather than a melting-recrystallization mechanism. The irreversible nature of the transition is attributed to the metastability of the β phase in the unstretched state. Different from the “β phases” that appear in polymers with stress-induced reversible transitions, e.g. poly(butylene terephthalate) and poly(butylene succinate), the stability of β phase in TPI is high that can be long-lived. The strain rate dependence of α-β transition hinders the determination of critical stress for the transition. It further indicates that the local stress within the sample is more heterogeneous at higher strain rates.
      PubDate: 2022-01-11
       
  • Memory Effect of Crystallization in 1-Butene/α-olefin Copolymers

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      Abstract: The macromolecular architecture is the crucial factor in determining the arrangement of the ordering structures, which, because of the multiscale feature, may exhibit distinct melting behaviors and induce the so-called memory effect to affect the following recrystallization. Until present, the correlation between the occurrence of memory effect and the intrinsic molecular structure is still far from the comprehensive understanding. In this work, four kinds of 1-butene/α-olefin random copolymers were designed and synthesized using the (pyridyl-amino) hafnium catalyst to introduce the different branches. The branch length was precisely controlled by the specific α-olefin comonomers, which include 1-hexene, 1-decene, 1-tetradecene, and 1-octadecene, while the branch density was tuned by the incorporation. As expected, the incorporation of α-olefin co-units to poly(1-butene) backbone decreases the non-isothermal crystallization kinetics and the degree of crystallinity. More interestingly, the resulting linear branch can induce the occurrence of memory effect and the threshold concentration of co-units (i.e., branch density) decreases with increasing the branch length. Based on the results of these 1-butene/α-olefin copolymers with designable branches, a direct correlation with the occurrence of memory effect and the fraction of amorphous region was established, which quantitatively indicates the degree of local segregation of the crystallized poly(1-butene) sequences by the α-olefin co-units.
      PubDate: 2022-01-11
       
  • Insertion of Supramolecular Segments into Covalently Crosslinked
           Polyurethane Networks towards the Fabrication of Recyclable Elastomers

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      Abstract: Thermoset plastics have become one of the most important chemical products in the world. The consequent problem is that although the thermosets possess excellent performance in mechanical strength, they cannot be reprocessed because of the internal permanent network structures. Optimizing the molecular design of thermosets is one of the most feasible ways to improve their recyclability. Here we present a facile and robust strategy to engineer the reprocessability of thermoset polyurethanes without compromising their mechanical toughness and chemical resistance via adding supramolecular additives during the polymer synthesis process. By using a multiple hydrogen bonding moiety as the model supramolecular additive, we demonstrate that the mechanical properties, recyclability, and chemical resistance of the crosslinked polyurethanes can be precisely controlled by adjusting the contents of the supramolecular additive. Systematic studies on the relations between molecular design and material properties are performed, and the optimized polyurethane network with a moderate amount of the supramolecular additive achieves the right balance between the robustness and recyclability. This work provides a cost-effective and practical way to chemically engineer thermoset plastics, aiming to enable the recycling of mechanically tough and chemically stable polymer materials.
      PubDate: 2022-01-11
       
  • Investigating the Effects of Para-methoxy Substitution in Sterically
           Enhanced Unsymmetrical Bis(arylimino)pyridine-cobalt Ethylene
           Polymerization Catalysts

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      Abstract: A group of five bis(arylimino)pyridine-cobalt(II) chloride complexes, [2-{(2,6-(Ph2CH)2-4-MeOC6H2)N = CMe}-6-(ArN = CMe)C5H3N] CoCl2 (Ar = 2,6-Me2C6H3Co1, 2,6-Et2C6H3Co2, 2,6-iPr2C6H3Co3, 2,4,6-Me3C6H2Co4, 2,6-Et2-4-MeC6H2Co5), each containing one N-4-methoxy-2,6-dibenzhydrylphenyl group and one smaller sterically/electronically variable N-aryl group, have been synthesized in good yield (>71%) from the corresponding neutral terdentate nitrogen-donor precursor, L1–L5. All complexes have been characterized by 1H-NMR and FTIR spectroscopy with the former highlighting the paramagnetic nature of these cobaltous species and the unsymmetrical nature of the chelating ligand. The molecular structures of Co3 and Co4 emphasize the steric differences of the two inequivalent N-aryl groups and the distorted square pyramidal geometry about the metal centers. In the presence of MAO or MMAO, Co1–Co5 collectively displayed high activities for ethylene polymerization producing high molecular weight polyethylenes that, in general, exhibited narrow dispersities (Mw/Mn values: 2.12–4.07). Notably, the least sterically hindered Co1 when activated with MAO was the most productive (6.92×106 gPE·mol−1(Co)·h−1) at an operating temperature of 60 °C. Conversely, the most sterically hindered Co3/MMAO produced the highest molecular weight polyethylene (Mw=6.29×105 g·mol−1). All the polymers displayed high linearity as demonstrated by their melting temperatures (>130 °C) and their 1H- and 13C-NMR spectra. By comparison of Co1 with its para-methyl, -chloro and -nitro counterparts, the presence of the para-methoxy substituent showed the most noticeable effect of enhancing the thermal stability of the catalyst.
      PubDate: 2022-01-11
       
  • Fractionated Crystallization Kinetics and Polymorphic Homocrystalline
           Structure of Poly(L-lactic acid)/Poly(D-lactic acid) Blends: Effect of
           Blend Ratio

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      Abstract: Stereocomplex (SC) crystallization has been an effective way to improve the physical performances of stereoregular polymers. However, the competition between homo and SC crystallizations can lead to more complicated crystallization kinetics and polymorphic crystalline structure in stereocomplexable polymers, which influences the physical properties of obtained materials. Herein, we select the medium-molecular-weight (MMW) poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA) asymmetric blends with different PDLA fractions (fD=0.01–0.5) as the model system and investigate the effects of fD and crystallization temperature (Tc) on the crystallization kinetics and polymorphic crystalline structure. We observe the fractionated (i.e., multistep) crystallization kinetics and the formation of peculiar β-form homocrystals (HCs) in the asymmetric blends under quiescent conditions, which are strongly influenced by both fD and Tc. Precisely, crystallization of β-form HCs is favorable in the MMW PLLA/PDLA blends with high fD (≥0.2) at a low Tc (80–100 °C). It is proposed that the formation of metastable β-form HCs is attributed to the conformational matching between β-form HCs and SCs, and the stronger constrain effects of precedingly-formed SCs in the early stage of crystallization. Such effects can also cause the multistep crystallization kinetics of MMW PLLA/PDLA asymmetric blends in the heating process.
      PubDate: 2022-01-11
       
 
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