Synergy between dynamic covalent boronic ester and boron-nitrogen coordination: strategy for self-healing polyurethane elastomers at room temperature with unprecedented mechanical properties.

Achieving mechanical robustness and highly efficient self-healing simultaneously at room temperature is always a formidable challenge for polymeric materials. Herein, a series of novel supramolecular polyurethane elastomers (SPUEs) are developed by incorporating dynamic covalent boronic ester and boron-nitrogen (B-N) coordination. The SPUEs demonstrate the highest tensile toughness (∼182.2 MJ m-3) to date for room-temperature self-healable polymers, as well as an excellent ultimate tensile strength (∼10.5 MPa) and ultra-high fracture energy (∼72 100 J m-2), respectively, owing to a synergetic quadruple dynamic mechanism. It is revealed that the B-N coordination not only facilitates the formation and dissociation of boronic ester at room temperature but also dramatically enhances the mechanical properties by the intermolecular coordinated chain crosslinking and intramolecular coordinated chain folding. Meanwhile, the B-N coordination and urethane hydrogen interaction also serve as sacrificial bonds, which rupture during stretching to dissipate energy and recover after release, leading to superior notch insensitiveness and recoverability. The SPUEs restore their mechanical robustness after self-healing at room temperature and the self-healing efficiency can be dramatically accelerated by surface wetting.

Calixarene-Functionalized Porous Carbon Aerogels for Polysulfide Capture: Cathodes for High Performance Lithium-Sulfur Batteries.

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.

A mechanically strong and tough anion exchange membrane engineered with non-covalent modalities.

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.

Shear-induced enhancements of crystallization kinetics and morphological transformation for long chain branched polylactides with different branching degrees.

The effects of long chain branching (LCB) degree on the shear-induced isothermal crystallization kinetics of a series of LCB polylactides (LCB PLAs) have been investigated by using rotational rheometer, polarized optical microscopy (POM) and scanning electron microscopy (SEM). Dynamic viscoelastic properties obtained by small-amplitude oscillatory shear (SAOS) tests indicate that LCB PLAs show more broadened relaxation time spectra with increasing LCB degree. Upon a pre-shear at the shear rate of 1 s(-1) LCB PLAs show much faster crystallization kinetics than linear PLA and the crystallization kinetics is enhanced with increasing LCB degree. By modeling the system as a suspension the quantitative evaluation of nucleation density can be derived from rheological experiments. The nucleation density is greatly enhanced with increasing LCB degree and a saturation in shear time is observed. Crystalline morphologies for LCB PLAs observed by POM and SEM demonstrate the enhancement of nucleation density with increasing LCB degree and a transformation from spherulitic to orientated crystalline morphologies. The observation can be ascribed to longer relaxation time of the longest macromolecular chains and broadened, complex relaxation behaviors due to the introduction of LCB into PLA, which is essential in stabilizing the orientated crystal nuclei after pre-shear.

More dominant shear flow effect assisted by added carbon nanotubes on crystallization kinetics of isotactic polypropylene in nanocomposites.

More dominant shear flow effect with different shear rates and shear time with assistance of added carbon nanotubes (CNTs) of low amounts on the crystallization kinetics of isotactic polypropylene (iPP) in CNT/iPP nanocomposites was investigated by applying differential scanning calorimetry (DSC), polarized optical microscopy (POM), and rheometer. CNTs were chemically modified to improve the dispersity in the iPP matrix. CNT/iPP nanocomposites with different CNT contents were prepared by solution blending method. The crystallization kinetics for CNT/iPP nanocomposites under the quiescent condition studied by DSC indicates that the addition of CNTs of low amounts significantly accelerates crystallization of iPP due to heterogeneous nucleating effect of CNTs, whereas a saturation effect exists at above a critical CNT content. The shear-induced crystallization behaviors for CNT/iPP nanocomposites studied by POM and rheometry demonstrate the continuously accelerated crystallization kinetics with assistance from added CNTs, with increasing CNT content, shear rate, and shear time, without any saturation effect. The changes of nucleation density for CNT/iPP nanocomposites under different shear conditions can be quantified by using a space-filling modeling from the rheological measurements, and the results illustrate that the combined effects of added CNTs and shear flow on the acceleration of crystallization kinetics are not additive, but synergetic. The mechanisms for the synergetic effect of added CNTs and shear flow are provided.

Supertough polylactide materials prepared through in situ reactive blending with PEG-based diacrylate monomer.

Supertough biocompatible and biodegradable polylactide materials were fabricated by applying a novel and facile method involving reactive blending of polylactide (PLA) and poly(ethylene glycol) diacylate (PEGDA) monomer with no addition of exogenous radical initiators. Torque analysis and FT-IR spectra confirm that cross-linking reaction of acylate groups occurs in the melt blending process according to the free radical polymerization mechanism. The results from differential scanning calorimetry, phase contrast optical microscopy and transmission electron microscopy indicate that the in situ polymerization of PEGDA leads to a phase separated morphology with cross-linked PEGDA (CPEGDA) as the dispersed particle phase domains and PLA matrix as the continuous phase, which leads to increasing viscosity and elasticity with increasing CPEGDA content and a rheological percolation CPEGDA content of 15 wt %. Mechanical properties of the PLA materials are improved significantly, for example, exhibiting improvements by a factor of 20 in tensile toughness and a factor of 26 in notched Izod impact strength at the optimum CPEGDA content. The improvement of toughness in PLA/CPEGDA blends is ascribed to the jointly contributions of crazing and shear yielding during deformation. The toughening strategy in fabricating supertoughened PLA materials in this work is accomplished using biocompatible PEG-based polymer as the toughening modifier with no toxic radical initiators involved in the processing, which has a potential for biomedical applications.