Geomimetics for green polymer synthesis: highly ordered polyimides via hydrothermal techniques

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Inspired by geological ore formation processes, we apply one-step hydrothermal (HT) polymerization to the toughest existing high-performance polymer, poly(p-phenyl pyromellitimide) (PPPI). We obtain highly-ordered and fully imidized PPPI as crystalline flakes and flowers on the micrometer scale. In contrast to classical 2-step procedures that require long reaction times and toxic solvents and catalysts, HT polymerization allows for full conversion in only 1 h at 200 °C, in nothing but hot water. Investigation of the crystal growth mechanismviascanning electron microscopy (SEM) suggests that PPPI aggregates formviaa dissolution–polymerization–crystallization process, which is uniquely facilitated by the reaction conditions in the HT regime. A conventionally prefabricated polyimide did not recrystallize hydrothermally, indicating that the HT polymerization and crystallization occur simultaneously. The obtained material shows excellent crystallinity and remarkable thermal stability (600 °C under N2) that stem from a combination of a strong, covalent polymer backbone and interchain hydrogen bonding

Molecular Mobility and Gas Transport Properties of Mixed Matrix Membranes Based on PIM-1 and a Phosphinine Containing Covalent Organic Framework

Polymers with intrinsic microporosity (PIMs) are gaining attention as gas separation membranes. Nevertheless, they face limitations due to their pronounced physical aging. In this study, a covalent organic framework containing λ5-phosphinine moieties, CPSF-EtO, was incorporated as a nanofiller (concentration range 0–10 wt %) into a PIM-1 matrix forming dense films with a thickness of ca. 100 μm. The aim of the investigation was to investigate possible enhancements of gas transport properties and mitigating effects on physical aging. The incorporation of the nanofiller occurred on an nanoaggregate level with domains up to 100 nm, as observed by T-SEM and confirmed by X-ray scattering. Moreover, the X-ray data show that the structure of the microporous network of the PIM-1 matrix is changed by the nanofiller. As molecular mobility is fundamental for gas transport as well as for physical aging, the study includes dielectric investigations of pure PIM-1 and PIM-1/CPSF-EtO mixed matrix membranes to establish a correlation between the molecular mobility and the gas transport properties. Using the time-lag method, the gas permeability and the permselectivity were determined for N2, O2, CH4, and CO2 for samples with variation in filler content. A significant increase in the permeability of CH4 and CO2 (50% increase compared to pure PIM-1) was observed for a concentration of 5 wt % of the nanofiller. Furthermore, the most pronounced change in the permselectivity was found for the gas pair CO2/N2 at a filler concentration of 7 wt %

Trapping virtual pores by crystal retro-engineering

Stable guest-free porous molecular crystals are uncommon. By contrast, organic molecular crystals with guest-occupied cavities are frequently observed, but these cavities tend to be unstable and collapse on removal of the guests—this feature has been referred to as ‘virtual porosity’. Here, we show how we have trapped the virtual porosity in an unstable low-density organic molecular crystal by introducing a second molecule that matches the size and shape of the unstable voids. We call this strategy ‘retro-engineering’ because it parallels organic retrosynthetic analysis, and it allows the metastable two-dimensional hexagonal pore structure in an organic solvate to be trapped in a binary cocrystal. Unlike the crystal with virtual porosity, the cocrystal material remains single crystalline and porous after removal of guests by heating

A diverse view of science to catalyse change:Valuing diversity leads to scientific excellence, the progress of science and, most importantly, it is simply the right thing to do. we must value diversity not only in words, but also in actions

No abstract available.publishe

A diverse view of science to catalyse change

Valuing diversity leads to scientific excellence, the progress of science and, most importantly, it is simply the right thing to do. We must value diversity not only in words, but also in actions

One-Pot Synthesis of High-Capacity Silicon-Lithium Anodes via On-Copper Growth of a Semi-Conducting, Porous Polymer

Silicon-based anodes with lithium ions as charge carriers have the highest predicted charge density of 3579 mA h g-1 (for Li15Si4). Contemporary electrodes do not achieve this theoretical value largely because conventional production paradigms rely on the mixing of weakly coordinated components. In this paper, a semi-conductive triazine-based graphdiyne polymer network is grown around silicon nanoparticles directly on the current collector, a copper sheet. The porous, semi-conducting organic framework (i) adheres to the current collector on which it grows via cooperative van der Waals interactions, (ii) acts effectively as conductor for electrical charges and binder of silicon nanoparticles via conjugated, covalent bonds, and (iii) enables selective transport of electrolyte and Li-ions through pores of defined size. The resulting anode shows extraordinarily high capacity at the theoretical limit of fully lithiated silicon. Finally, we combine our anodes in proof-of-concept battery assemblies using a conventional cathode, NCM811