Combing experimental methods and molecular simulations to study self-healing behaviors of polyurethane elastomers containing multiple hydrogen bond networks and flexible blocks

The preparation of polymers with high self-healing ability is conducive to environmental protection and resource conservation. In the present work, two kinds of polyurethane (PU) elastomers were prepared: the one containing flexible end blocks (polypropylene glycol) and the other containing flexible end blocks and 2-ureido-4[1H]-pyrimidinone (UPy) groups that can form reversible quadruple hydrogen bonds. Both of the two PU elastomers have self-healing ability. At low temperatures the PU without UPy groups exhibits stronger self-healing ability, while at high temperatures the PU with UPy groups has better self-healing function. The difference can be attributed to the combined effect of segmental mobility and reversible network strength. Based on molecular simulations, we further observed that the self-healing behaviors are affected by four factors: healing temperature, reversible interaction strength, reversible interaction site density and segment diffusion ability.

Halogen-bonded shape memory polymers

Halogen bonding (XB), a non-covalent interaction between an electron-deficient halogen atom and a Lewis base, is widely adopted in organic synthesis and supramolecular crystal engineering. However, the roadmap towards materials applications is hindered by the challenges in harnessing this relatively weak intermolecular interaction to devise human-commanded stimuli-responsive soft materials. Here, we report a liquid crystalline network comprising permanent covalent crosslinks and dynamic halogen bond crosslinks, which possess reversible thermo-responsive shape memory behaviour. Our findings suggest that I···N halogen bond, a paradigmatic motif in crystal engineering studies, enables temporary shape fixation at room temperature and subsequent shape recovery in response to human body temperature. We demonstrate versatile shape programming of the halogen-bonded polymer networks through human-hand operation and propose a micro-robotic injection model for complex 1D to 3D shape morphing in aqueous media at 37 °C. Through systematic structure-property-performance studies, we show the necessity of the I···N crosslinks in driving the shape memory effect. The halogen-bonded shape memory polymers expand the toolbox for the preparation of smart supramolecular constructs with tailored mechanical properties and thermoresponsive behaviour, for the needs of, e.g., future medical devices.

Exploring halogen⋯halogen interactions in supramolecular self-assemblies of BODIPY networks

In this study, the efficiency of halogen⋯halogen interactions to control supramolecular assemblies of boron dipyrromethene (BODIPY) (B1–B5) derivatives was explored.

Halogen bonding in polymer science: towards new smart materials

The halogen bond is a special non-covalent interaction, which can represent a powerful tool in supramolecular chemistry. Although the halogen bond offers several advantages compared to the related hydrogen bond, it is currently still underrepresented in polymer science. The structural related hydrogen bonding assumes a leading position in polymer materials containing supramolecular interactions, clearly indicating the high potential of using halogen bonding for the design of polymeric materials. The current developments regarding halogen bonding containing polymers include self-assembly, photo-responsive materials, self-healing materials and others. These aspects are highlighted in the present perspective. Furthermore, a perspective on the future of this rising young research field is provided.

The incorporation of halogen bonding into polymer architectures is a new approach for the design of functional materials. This perspective emphasizes the current development in the field of halogen bonding featuring polymer materials.

Halogen-Bonded BODIPY Frameworks with Tunable Optical Features*

The ability to tune the optical features of BODIPY materials in the solid state is essential for their photorelated application and requires efficient control of the crystal packing. In this study, such control of BODIPY supramolecular assemblies was achieved by deliberate design and synthesis of a BODIPY containing a strong halogen-bond (XB) acceptor (-NO₂ ) and donor (I, Br) to mediate XB interactions. The di-halogenated structures formed isostructural mono-coordinate motif B3, B4 (1D tubular structure) and symmetric bifurcated motif B4-II (1D zigzag chains structure) through N-O⋅⋅⋅I, Br XB interactions. These XB interactions promote singlet-to-triplet intersystem crossing and triplet-to-singlet reverse intersystem crossing due to partial delocalization of oxygen electrons onto Br and I, which leads to unexpected fluorescence enhancement of B4-II. Finally, the indirect optical band gaps of B3, B4 and B4-II were amenable to tuning in the range of 1.85-2.50  eV by XB-driven crystal packings.

Modulation of supramolecular self-assembly of BODIPY tectons via halogen bonding

In this study, the efficiency of halogen bonding strategies to control over the supramolecular assemblies of boron dipyrromethene (BODIPY) (B-1, B-2, and B-3) derivatives was explored.

Novel Biobased Self-Healing Ionomers Derived from Itaconic Acid Derivates

This article presents novel biobased ionomers featuring self-healing abilities. These smart materials are synthesized from itaconic acid derivates. Large quantities of itaconic acid can be produced from diverse biomass like corn, rice, and others. This study presents a comprehensive investigation of their thermal and mechanical properties via differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), and FT-Raman and FT-IR measurements as well as dynamic mechanic analysis. Within all these measurements, different kinds of structure-property relationships could be derived from these measurements. For example, the proportion of ionic groups enormously influences the self-healing efficiency. The investigation of the self-healing abilities reveals healing efficiencies up to 99% in 2 h at 90 °C for the itaconic acid based ionomer with the lowest ionic content.

Halogen bonding for molecular recognition: new developments in materials and biological sciences

This review highlights recent developments of halogen bonding in materials and biological sciences with a short discussion on the nature of the interaction.

Halogen bonding driven crystal engineering of iodophthalonitrile derivatives

Various halogen bonding driven crystal structures can be obtained by simple modifications of iodophthalonitrile derivatives.