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ABSTRACT The mobility of free macromolecular chains is of importance to the growth of crystallites in a crystallizing sustainable polylactide (PLA), which was scarcely explored by rheology. In this study, the time-resolved rheological properties for PLA during isothermal crystallization were investigated first, showing that the storage and loss modulus experience 2-3 decades of increase. The Avrami analysis reveals that the crystallization kinetics in rheological measurement protocol follows the homogeneous nucleation and three-dimensional growth mechanism. The linear viscoelastic properties in the vicinity of physical gelation point were then studied at the inverse quenching temperature of 165 °C. The results show that physical gelation occurs when the critical absolute crystallinity reaches 13% as determined by the rheological method. Relaxation time spectra reveal that the interfacial relaxation is greatly retarded but the presence of growing spherulites possesses little constraint on the mobility of free chains in matrix especially before physical gelation point. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1235-1244 [ABSTRACT FROM AUTHOR]

A tri-arm star-shaped oligomer with PEG arm and imidazolium-based ionic liquid moiety (TSIL) was introduced in poly(lactic acid) (PLA) blends, and the synergetic effects of PEG arm and IL moiety contained in the TSIL on the crystallization behaviors of PLA were investigated by DSC and POM. The results determined by DSC show that TSIL inhibits the crystallization of PLA when the mass content of TSIL in blend is as low as 1 mass%, while the crystallization process is accelerated greatly with increasing mass content of TSIL. As revealed by POM observations, the spherulitic morphology remains unchanged in TSIL/PLA blends and the nucleation and growth of spherulites are altered due to the different effects of PEG arm and IL moiety. The nucleation process is suppressed by IL moiety, while the growth rate of spherulites is improved because of the plasticizing effect of PEG arm. The synergistic effects of PEG arm and IL moiety contained in the TSIL also contribute to the acceleration of kinetics in non-isothermal crystallization process. [ABSTRACT FROM AUTHOR]

Aneasy procedure was applied to prepare high-melt-strength polylactide(PLA) that involves γ-radiation-induced free-radical reactionsto introduce a long-chain branched structure onto a linear PLA precursorwith addition of a trifunctional monomer, trimethylolpropane triacrylate(TMPTA). The results from size-exclusion chromatography coupled withmultiangle laser light scattering (SEC-MALLS) detection indicate thatthe resultant long-chain branched PLA (LCB PLA) samples have an increasedmolecular mass and an elevated branching degree with increasing amountof TMPTA incorporated during the irradiation process. Various rheologicalplots including viscosity, storage modulus, loss tangent, Cole–Coleplots, and weighted relaxation spectra were used to distinguish theimproved melt strength for LCB PLA samples. The effect of LCB structureon elongational rheological properties was further investigated. TheLCB PLA samples exhibited an enhancement of strain-hardening underelongational flow. The enhanced melt strength substantially improvedthe foaming performance of the LCB PLA samples. [ABSTRACT FROM AUTHOR]

The effects of long chain branchingon the nucleation density enhancements and morphological evolutionfor polylactide (PLA) materials during shear-induced isothermal crystallizationprocess were thoroughly investigated by using rotational rheometerand polarized optical microscopy (POM). Shear-induced nucleation densityenhancements for the long chain branched PLA (LCB PLA) were studiedon the basis of the determination of the critical shear rate, forwhich the stretch of the longest chains of the linear component isexpected. The results of shear-induced isothermal crystallizationkinetics show that the crystallization process under shear is greatlyenhanced compared to the quiescent conditions and the crystallizationkinetics is accelerated with the increases in shear rate and/or sheartime. LCB PLA crystallizes much faster than linear PLA under the sameshear condition. A saturation effect of shear time on crystallizationkinetics is observed for both linear PLA and LCB PLA. In-situ POMobservations demonstrate that LCB PLA not only possesses higher nucleationdensity under the identical shear time and a constant lower valueof spherulitic growth rate compared with that of linear PLA but alsoforms the shish-kebab structure after sheared for sufficient time.The quantitative evaluation of the shear-induced nucleation densitiesfrom rheological measurements is based on the space-filling modelby using the Avrami equation, and the obtained nucleation densityvalues are well consistent with that estimated from POM observations.A saturation of nucleation density under shear can be reached forboth linear PLA and LCB PLA. The saturated nucleation density valuesare higher than that under the quiescent condition by a factor ofover 3 orders of magnitude, and the saturated nucleation density valuefor LCB PLA is more than that for linear PLA by a factor of 1 orderof magnitude under the same shear condition. The enhancement of nucleationability and the morphological evolution from the spherulitic to shish-kebabstructures induced by shear flow can be ascribed to the broadenedand complex relaxation behaviors of LCB PLA. [ABSTRACT FROM AUTHOR]

Constructing segregated pathways in the conductive polymer composites (CPCs) is efficient to achieve satisfactory electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) with low content of nanofillers. Conventionally, most of segregated CPCs were based on thermoplastics and precisely controlled processing conditions were essential to achieve structural integrity and mechanical robustness. Herein, by taking the advantage of the associative dynamic bonding rearrangement in the epoxy vitrimer, we fabricated segregated MWCNTs/epoxy composites in a wide range of compression temperature and pressure. The segregated CPCs show a low conductive percolation threshold at 0.066 wt% and an EMI SE of 22 dB when only 2 wt% of MWCNTs were loaded. More promisingly, the mechanical robustness was achieved by the volatile ethylene glycol (EG) involved decomposition and repolymerization of β -hydroxyl ester at the interface even when numerous MWCNTs were in between. The segregated structure and macroscopic properties can be reserved after reprocessing and the nanofillers can be recovered with excessive EG at elevated temperature. [Display omitted] • The integrated segregation of MWCNTs in vitrimer composites can be maintained in a broad range of processing conditions. • The nanocomposites demonstrated a low conductive percolation threshold and excellent EMI shielding performance. • The mechanical robustness was achieved by the decomposition and repolymerization of b -hydroxyl ester at the interface. • The segregated structure and macroscopic properties can be reserved after reprocessing. • The nanofillers can be recovered after alcoholysis at elevated temperature. [ABSTRACT FROM AUTHOR]

Poly (l -lactide) (PLLA) based ternary nanocomposites were fabricated by introducing in situ crosslinked poly(ethylene glycol) diacrylate (CPEGDA) as the rubbery toughening modifier and multiwall carbon nanotubes (MWCNTs) as the conductive fillers. Due to the incorporation of MWCNTs, the domain size of CPEGDA became smaller and MWCNTs were selectively distributed in PLLA continuous phase, facilitating to balance the stiffness and toughness. Rheological investigation showed that the formation of a double network of CPEGDA and MWCNTs resulted in constrained molecular mobility, thus greatly increasing the modulus and viscosity at low frequencies and long-time relaxation strength. The low percolation threshold of MWCNTs in electrical conductivity was found to be 0.19 vol% and the electromagnetic interference shielding effectiveness (EMI SE) of 26.4 dB was achieved with incorporating 2.4 vol% of MWCNTs. This work could provide a novel way to fabricate PLLA based eco-friendly nanocomposites with simultaneous superior mechanical properties and excellent EMI shielding performance. [ABSTRACT FROM AUTHOR]

Thermoplastic polyurethane elastomers (PUEs) consisting of biodegradable poly (ε-caprolactone) (PCL) and low toxic aliphatic diisocyanates are of great potential in biomedical applications, but the inferior mechanical strength and elastic recovery at large strain have limited their practical utilization. Inspired by the outstanding thermal and mechanical properties of stereocomplex (SC) PLA, a thermoplastic PUE that contains SC crystallites (SC-PU) was prepared via racemically blending the PLA stereoisomers-based polyurethanes. The formation of SC crystallites in SC-PU was confirmed by WAXD and ATR-FTIR techniques. The effects of stereocomplexation on its thermal, morphological and mechanical properties were investigated. The results show that the SC crystalline domains, acting as ‘additional reinforcing phases’, endow the improved performance of SC-PU in tensile strength, Young's modulus, elastic recovery, and other properties. This study may provide a new method to improve the inferior mechanical properties of biodegradable PUEs based on PCL and aliphatic diisocyanates, which can contribute to the expansion of their applications in widespread fields. [ABSTRACT FROM AUTHOR]

Isothermal crystallization processes in the temperature range from 110 to 140 °C were studied by using polarizing optical microscopy (POM) for poly(l-lactide) (PLLA) film samples with and without confinement conditions. The PLLA film samples were prepared by melt pressing between two cover glasses to provide the surface confinements and by removing the top cover glasses or by solution cast to keep the top surface free of confinements, respectively. Through carefully following the changes of spherulite radius with crystallization time, it is surprisingly found that there exists an acceleration of spherulitic growth rates at the late stage following the normal spherulitic growth rates at the early stage of isothermal crystallization for PLLA film samples with both surface confinement (by cover glasses) and planar confinement conditions (by aggregation of adjacent spherulites to form “lake-like” regions) at certain temperatures, while the spherulitic growth rates remain constant at each isothermal crystallization temperature for PLLA film samples without the confinement conditions. On the basis of data analyses on the spherulitic growth rates under various conditions from several different aspects, it is finally concluded that the decreases of glass transition temperature induced by crystallization under confinement conditions during isothermal crystallization of PLLA film samples cause the peculiar spherulitic growth rate acceleration at the late stage. [ABSTRACT FROM AUTHOR]

Striving for high-performance polyurethanes from renewable resources has attracted increasing attention, due to the continuously increased environmental concerns and resource crisis related to traditional fossil-based materials. Castor oil is a renewable raw material, while the traditional castor oil-based polyurethane chains are highly flexible and permanently cross-linked, resulting in poor mechanical strength and toughness that cannot be reprocessed. To obtain robust and reprocessable castor oil-based polyurethane materials, herein we report the utilization of supramolecular nitrogen-coordinated boronic ester crosslinking. A series of castor oil-based polyurethane (COPUX) vitrimers with different amounts of dynamic covalent boronic ester crosslinking and boron-nitrogen (B-N) coordination were designed and synthesized by a solvent- and catalyst-free two-step method. The permanent crosslinking degree decreases while the strength, moduli, ductility and heat resistance significantly increase accordingly with increasing boronic ester content. The B-N coordination can further improve the mechanical properties of materials due to supramolecular interactions. The tensile behaviors are tunable over a broad range (either as elastomers or as plastics) depending on the compositions. The tensile strength of COPU4 was improved by 9 times from 1.9 to 17.1 MPa compared to COPU0. The Young's modulus for COPU3 was improved by 119 times from 2.9 to 345.1 MPa and the yield strength reaches 18.3 MPa. Boron-nitrogen coordination enhances mechanical strength without loss of material self-healing properties. COPU3 and COPU4 exhibit excellent self-healing as well as reprocessability. The investigation provides the feasibility of future shifts from traditional fossil-based thermosets to bio-based reprocessable vitrimers, offering new hints for the design and manufacture of high-value sustainable polymer materials. • Castor oil-based polyurethane vitrimers were prepared by a solvent- and catalyst-free two-step method. • The supramolecular nitrogen-coordinated dynamic covalent boronic ester was incorporated. • Robustness, reprocessing and self-healing were achieved simultaneously. [ABSTRACT FROM AUTHOR]

A cage‐type composite was successfully prepared by attaching p‐sulfonatocalix[4]arene to a porous activated carbon aerogel (ACA). The resulting composite showed a high specific surface area of 1620.7 m2 g−1 and a high sulfur loading of 2.5 mg cm−2. The calixarene is uniformly dispersed on the carbon spheres and efficiently captures polysulfides by interaction with the sulfonate groups. Meanwhile, the cross‐linked porous structure of the composite restricts the migration of polysulfides. The cathode delivers an outstanding electrochemical performance with an initial capacity of 1304.7 mAh g−1 at 0.2 C. Furthermore, it displays excellent long‐term cycling stability, maintaining 884.7 mAh g−1 after 300 cycles at 0.5 C. Density functional theory (DFT) adsorption calculations support the strong interaction between the calixarenes and polysulfides and reveal the capture mechanism. [ABSTRACT FROM AUTHOR]

To meet the increasing concerns for health, safety, and the environment, traditional solvent coatings are gradually replaced by their waterborne counterparts and the development of robust and self-healing waterborne polymers is showing important application significance. Herein, waterborne polyurethane urea composite coatings (WPUU) with dynamic hindered urea bonds are reported. The dispersion of WPUU synthesized with hindered amine as the chain extender has a smaller particle size. The mussel-inspired polydopamine modification was applied to improve the dispersion and interfacial interactions of carbon nanotubes (CNTs) in the WPUU matrix. Due to the dynamic reversibility of the hindered urea and abundant hydrogen bonding, the resulting WPUU-2T2B can achieve self-healing at 70 °C, also showing good mechanical toughness, the tensile strength of 34.0 MPa and elongation at break of 530 %. After adding the modified CNTs, 10%PDA@CNTs/WPUU demonstrates the tensile strength of 22.4 MPa, elongation at break of 251 % and yield strength of 13.1 M Pa. The self-healing properties of nanocomposites are still retained. The maximum electrical conductivity of the composite coating reaches 56.8 S m−1. The composite coating can recover excellent corrosion resistance in the electrolyte environment after healing, which could ensure its safety and sustainability in the long-term service. We envisage this work offers an idea for the fabrication of environmentally friendly, self-healing, corrosion resistant and electrically conductive coatings with good thermal stability and robust mechanical properties. • Robustness and self-healing of waterborne polyurethane urea is achieved by incorporating dynamic hindered urea. • Polydopamine was applied to improve the dispersion and interfacial interactions of CNTs in the WPUU matrix. • The composite coating shows increased electrical conductivity and corrosion resistance as well as self-healing capability. [ABSTRACT FROM AUTHOR]

A mechanically robust and tough anion exchange membrane was constructed using the strategy of supramolecular modalities. After introducing a secondary amide as a hydrogen-bonding crosslinking motif into the side chain of the PPO backbone, the membrane exhibits high mechanical strength and excellent flexibility (101% elongation at break), as well as suppressed water uptake, enhanced thermal stability and good fuel cell performances. [ABSTRACT FROM AUTHOR]

In the pursuit of alkali stable cation as functional group for anion exchange membranes (AEMs), a novel adamantammonium (AdA) cation, which replacing methyl group of conventional trimethylammonium by an adamantyl group, was synthesized and investigated. 1 H NMR spectroscopy was employed to quantify the extent of decomposition and the results showed that > 99% adamantammonium remaining after 7 days immersion in 2 M NaOH (in D 2 O) at 80 °C. The AdA functionalized benzyl type poly(2,6-dimethyl phenylene oxide) polyelectrolytes, PPO-AdAs, were further prepared and characterized the AEM properties. Not only the chemical durability of these new PPO-AdA membranes, interestingly, but the conductivity and dimensional stability (water uptake and in-plane swelling) are superior to the benzylmethylammonium-benchmark PPO-based AEM (PPO-TMA). With the similar IEC values, the water uptake of PPO-AdA-41 sample is much lower than PPO-TMA-28, however, the conductivity of the former (15.7 mS cm -1 , chloride conductivity at 50 °C) is higher than the latter (13.3 mS cm -1 ). Overall, the results of this study offer a base-stable cation, adamantammonium, and the corresponding adamantammonium-based AEMs for fuel cell applications with the advantages of chemical stability, enhanced conductivity and excellent dimensional stability as well as facial functionalization technique. [ABSTRACT FROM AUTHOR]

Polyurethane elastomer nanocomposites are strategically important due to their indispensable applications in daily life and high-tech fields. Herein, a series of nanocomposites with extraordinary strength, toughness and energy dissipation are reported, which are enabled by multiple dynamic moieties including dynamic boronic ester covalent bonds, boron-nitrogen coordination bonds in the matrix and on the interface. The surface-modified silica nanoparticles with amino-silane coupling agent (D-SiO 2) were added to the polyurethane matrix that contains boron-nitrogen coordination. The presence of interfacial coordination significantly improves the dispersion of D-SiO 2 and enhances the interface interaction of polyurethane composites (SPU/D-SiO 2), which is evidenced by scanning electron microscopy, transmission electron microscopy and rheological investigation. Through mechanical experiment analysis, these modified polyurethane composites exhibit high tensile strength and toughness. The tensile strength of SPU/10D-SiO 2 increases to 19.5 ± 0.2 MPa and its tensile toughness achieves 216.9 MJ/m3, which is 35% of increase as compared with the pristine SPU that had a record-high toughness. In addition, the coordination bonds in the matrix and interface in the composites provide versatile and efficient energy dissipation during the tensile process. This work offers a facile method to improve the mechanical robustness of the newly developed supramolecular polyurethane elastomers. [Display omitted] • The interfacial coordination significantly improves the dispersion of D-SiO 2 and enhances the interfacial interaction. • The tensile toughness of SPU/10D-SiO 2 achieves 216.9 MJ/m3, which is 35% of increase as compared with the pristine SPU. • The extraordinary strength, toughness and energy dissipation are enabled by multiple dynamic moieties. [ABSTRACT FROM AUTHOR]

Consideringthat multiwalled carbon nanotubes (MWCNTs) can be usedas anisotropic and stiff nano-objects acting as minority physicalcross-linking points dispersed in soft polymer grafting matrixes,a series of copolymer-grafted multiwalled carbon nanotube compositethermoplastic elastomers (CTPEs), MWCNT-graft-poly(n-butyl acrylate-co-methyl methacrylate)[MWCNT-g-P(BA-co-MMA)], with minorMWCNT contents of 1.2–3.8 wt % was synthesized by the surface-initiatedactivators regenerated by electron transfer for atom-transfer radicalpolymerization (ARGET ATRP) method. Excellent dispersion of the MWCNTsin the CTPEs was demonstrated by SEM and TEM, and the thermal stabilityproperties and glass transition temperatures of the CTPEs were characterizedby thermogravimetric analysis (TGA) and differential scanning calorimetry(DSC), respectively. Mechanical property test results demonstratedthat the CTPEs exhibit obviously enhanced mechanical properties, suchas higher tensile strength and elastic recovery, as compared withtheir linear P(BA-co-MMA) copolymer counterparts.The microstructural evolutions in the CTPEs during tensile deformationas investigated by in situ small-angle X-ray scattering (SAXS) revealedthe role of the MWCNTs, which can provide additional cross-linkingpoints and transform soft elastomers into strong ones. [ABSTRACT FROM AUTHOR]

[Display omitted] • Achieving full degradability of polylactide blends using biodegradable polyurethane elastomers as the toughening modifier. • The morphology of minor phase and matrix crystallization in PLLA blends is regulated significantly by interfacial sc-PLA. • The superior toughness is achieved at the optimized D-PU content after thermal annealing. • The toughening mechanism and degradation performance reveal the importance of interfacial stereocomplexation of PLA. The degradable polyurethane elastomers containing poly (L-lactide) (L-PU) and poly (D-lactide) (D-PU) were synthesized and incorporated in commercial PLLA as the toughening modifier. The stereocomplexation of PLA (sc-PLA) is successfully achieved at the interface of PU and PLLA domains in a single melt-blending process. The morphology and matrix crystallization in PLLA/D-PU blends is significantly improved by the presence of interfacial sc-PLA, showing morphological evolution to strip-shaped dispersion of PU phase and remarkable acceleration in matrix crystallization kinetics. After incorporating D-PU, the mechanical properties of blends are improved by interfacial sc-PLA, demonstrating that the notched Izod impact strength increases from 11.8 ± 3.1 KJ/m2 of PLLA/L-PU15 to 27.0 ± 5.8 KJ/m2 of PLLA/D-PU15 and even greater enhancement after thermal annealing is achieved. By observing the morphology of the impact fracture surface, the toughening mechanism of D-PU is investigated, revealing that the superior interfacial strength facilitates shear yielding of non-annealed sample and further prohibits de-bonding of rubber phase after thermal annealing. Hydrolysis tests in alkaline environment show that although interfacial sc-PLA can retard the hydrolysis rate, the blends still experience rapid weight loss to achieve full degradation. This work provides a highly effective strategy to toughen PLLA without sacrificing its degradability. [ABSTRACT FROM AUTHOR]

Anion exchange membrane (AEM) is a key component of polyelectrolyte electrochemical devices that operates under alkaline conditions. AEMs that can endure in harsh caustic and oxidative environments while exhibiting mechanical robustness and high ion conductivities are highly desired. In this study, we present a series of poly(quinquephenylene- co -diphenylene piperidinium) (PQDP) AEMs that have excellent alkaline and oxidative stabilities. Specifically, this membrane can retain its conductivity after 30 days aging in 1 M NaOH solution at 80 °C as well as over 95% of the initial mass after treatment in Fenton's reagent at 80 °C for 5 h. Moreover, the excellent mechanical properties (Young's modulus ~ 1 GPa, tensile strength > 40 MPa) are also observed for PQDP membranes. The heteroatom linkage-free backbone as well as the high contents of arylene units are responsible for the chemically and mechanically stable PQDP membranes. A PQDP membrane with the highest IEC (PQDP-3, 2.44 mmol g−1) demonstrate a high anion conductivity in Cl− form (73 mS cm−1 at 90 °C). Based on the high performance of PQDP membranes, a fuel cell prototype using PQDP-3 shows a high peak power density of 507 mW cm−2 at 80 °C with a current density of 0.97 A cm−2. [Display omitted] • Novel poly(arylene piperidinium)s with rich phenylene units were synthesized. • The PQDP membrane showed excellent oxidative stability and alkaline durability. • A peak power density of 507 mW cm−2 was achieved for PQDP-3 membrane. [ABSTRACT FROM AUTHOR]

Anion exchange membrane (AEM) is a key component for energy-conversion devices that enabling the use of non-noble electrocatalysts. After more than a decade of pursuit in alkaline-stable and high anion-conducting ionomers, aryl ether-free polyaromatics offer a promising candidate as an advanced AEM for use in fuel cell and electrolyzers. However, the traditional trade-off dilemma between conductivity and stability (e.g., chemical, dimensional, and mechanical stabilities etc.) of the membrane still remains. Here, we introduced a flexible bication cross-linker to doubly quaternary ammonium-tethered poly(meta -terphenylene alkylene) ionomers with high ion contents, aiming to improve the chemical and dimensional stabilities without compensate the ion-conducting merits. The designed flexible bication cross-linker is responsible for the microphase-separated morphology preservation in the cross-linked membranes. Although the water absorption decreased significantly as cross-linking content increasing, the ion conductivity of the cross-linked AEM was well retained, especially at elevated temperatures. Moreover, after cross-linking, a notable increase in chemical stability was observed, and the m -XPTPA40-2N with highest cross-linking density exhibited the best alkaline and oxidative stabilities. Owing to the mechanical robustness and high conductivity, a fuel cell fabricated with cross-linked membrane m -XPTPA40-2N showed a maximum power density of 302 mW cm−2 at a current density of 614 mA cm−2. Overall, the results of this study provide a simple but efficient strategy to improve the performance of AEM. Image 1 • A flexible bication cross-link was introduced to mitigate the dilemma between ion conductivity and dimensional integrity. • The morphology of AEM was well preserved after cross-linking. • Bication cross-linked AEMs showed excellent chemical durability. • A H 2 –O 2 fuel cell based on m -XPTPA40-2N AEM showed a peak power density of 302 mW cm−2. [ABSTRACT FROM AUTHOR]

A novel organic composite coating was successfully fabricated through in situ mineralizing in artificial seawater for a lasting anti-corrosive coating. The mineralized composite films make full use of the advantages including rich hydroxyl group and special ring structure of β-cyclodextrin as well as superior adhesion and high flexibility of waterborne polyurethane coating. The results show the β-CD remarkably promotes the mineralization of CaCO 3 on WPU substances through the effective adsorption and complexation of hydrophobic cavity to calcium ions. The dense organic-inorganic composite film exhibits outstanding anti-corrosive performance with corrosion rate of 1.39 × 10−3 mm/year for 3CD-WPU sample, being much less than 7.36 × 10−2 mm/year for WPU coating under same conditions. The excellent anti-corrosion performance is mainly attributed to the uniform nucleation site provided by CD-WPU and further formation of dense CaCO 3 film. Furthermore, the radial distribution function and adsorb energy theoretic analysis by molecular dynamic simulation definitely reveal and support the mechanism of β-CD promoting the CaCO 3 mineralization. Unlabelled Image • A novel polyurethane-CaCO 3 film is developed via in situ mineralizing in seawater. • The compact self-healing film effectively improves anti-corrosion performance. • β-Cyclodextrin with rich hydroxyl and hydrophobic cavity promotes mineralization. • The mechanism via adsorption is firmly supported by molecular dynamic simulation. [ABSTRACT FROM AUTHOR]