Synthesis of Diverse Polycarbonates by Organocatalytic Copolymerization of CO2 and Epoxides: From High Pressure and Temperature to Ambient Conditions.

Organophosphazenes combined with triethylborane (TEB) were selected as binary organocatalyts for the copolymerization of CO2 and epoxides. Both the activity and selectivity were highly dependent on the nature of phosphazenes. 2,4,6-Tris[tri(1-pyrrolidinyl)-iminophosphorane]-1,3,5-triazine (C3 N3 -Py-P3 ) with a relatively low basicity (pKa =26.5 in CD3 CN) and a bulky molecular size (φ=1.3 nm) exhibited an unprecedented efficiency (TON up to 12240) and selectivity (>99 % polymer selectivity and >99 % carbonate linkages) toward copolymerization of CO2 and cyclohexene oxide (CHO), and produced CO2 -based polycarbonates (CO2 -PCs) with high molar masses (Mn up to 275.5 kDa) at 1 MPa of CO2 and 80 °C. Surprisingly, this binary catalytic system achieved efficient CO2 /CHO copolymerization with TOF up to 95 h-1 at 1 atm pressure and room temperature.

Rejuvenation of Electrochromic Devices.

Electrochromic devices (ECDs) are a hot pot due to their significant energy-saving effect in green buildings. However, the ECDs suffer from degradation induced by ion trapping during cycling, which restricts their further development. Here, it is demonstrated that the electrochromic performance of the degraded ECDs can be rejuvenated by heat treatment method The release mechanism of trapped ions in films is simulated and validated using three types of ECDs. The semi-solid-state ECD evinces a state of near-failure at low temperatures can regain its initial performance by heating. All-solid-state ECDs, including amorphous WO3 (a-WO3 ECD) and crystalline WO3 (c-WO3 ECD) as the electrochromic layer, can also release the trapped ions and regain the performance (97.3% and 95.5% of initial optical modulation) by annealing, regardless of the way of degradation. The research has extended the lifespan of multiple ECDs, providing significant practical value and promoting sustainable, and eco-friendly development.

Analysis of Thermal Stress in Vanadium Dioxide Thin Films by Finite Element Method.

The buckling, de-lamination, and cracking of the thin film/substrate system caused by thermal stress is the main obstacle for functional failure. Moreover, the thermal stress of vanadium dioxide (VO2) thin film may be more complicated due to the stress re-distribution caused by phase transition. Therefore, the thermal stress of VO2 thin films deposited on four substrates with different materials (fused silica, silicon slice, sapphire, and glass) has been studied by finite element method in the present work. The influences of external temperature, substrate, and interlayer on thermal stress were analyzed. It was found that the substrates can greatly affect the thermal stresses, which were mainly caused by the mismatch of coefficient of thermal expansion (CTE). The thermal stress had a linear relationship with the external temperature, but this tendency would be redistributed or even change direction when phase transition occurred. The simulated results were in tandem with the analytical method. Meanwhile, the radial stress and shear stress distribution under the influence of phase transition were calculated. In addition, the reduction of thermal stress and shear stress showed that the appropriate interlayer can enhance the adhesive strength effectively.

Synthesis of Tris-Phosphazene Bases with Triazine as Core and Their Applications for Efficient Ring-Opening Alternating Copolymerization of Epoxide and Anhydride: Notable Effect of Basicity and Molecular Size.

Phosphazenes as organocatalysts for the synthesis of polymers have evolved to powerful tools, and their catalytic performances highly depend on the basicity and molecular structure (size and shape). Therefore, designing phosphazenes with tunable basicity and molecular structure is greatly promising for the development of organocatalysts with improved catalytic properties, for example, high activity and selectivity. In this contribution, 2,4,6-tris[tri(dimethylamino)iminophosphorane]-1,3,5-triazine (C3N3-Me-P3) and 2,4,6-tris[tri(1-pyrrolidinyl)iminophosphorane]-1,3,5-triazine (C3N3-Py-P3) containing a 1,3,5-triazine-core were designed and synthesized. NMR spectroscopy analysis and single-crystal X-ray diffractions reveal that C3N3-Me-P3 and C3N3-Py-P3, particularly the latter, show relatively low basicity, similar as t-BuP1, but have a bulky molecular size, similar as t-BuP4. C3N3-Me-P3 and C3N3-Py-P3 were successfully employed as organocatalysts for the ring-opening alternating copolymerization (ROAC) of anhydrides and epoxides with high activity. The produced polyesters were characterized using NMR spectroscopy, GPC and MALDI TOF, revealing perfectly alternating sequence, controlled molar mass and low dispersity and suggesting highly controlled ROAC reactions. Thus, well-defined triblock polyester P(PA-alt-CHO)-b-P(PA-alt-PO)-b-P(PA-alt-CHO) was facilely synthesized by one-pot reaction via sequential addition of two different epoxides.

Inorganic all-solid-state electrochromic devices with reversible color change between yellow-green and emerald green.

All-solid-state electrochromic devices with the structure of glass/ITO/WO3/Ta2O5/Li/V2O5/ITO were prepared by an evaporation method. Because of the use of a V2O5 complementary layer, the ECD can achieve obvious color change between yellow-green and emerald green with superior cycling performance up to 5000 cycles, indicating the great potential in smart window applications.

Detection of Homologue and Isomer Vapors through Dynamic Reflection Spectra of Hollow Mesoporous Silica Sphere Photonic Crystals.

Vapors of homologues and isomers with very similar refractive indices can be easily distinguished by using dynamic reflection spectra (DRS) of hollow mesoporous silica sphere (HMSS) photonic crystals (PCs). Different diffusion behaviors render the HMSS PCs with a distinct response to different chemicals vapors, leading to diversity in the evolution of the reflection spectra and their DRS patterns. Therefore, by studying the geometric characteristics and color changes of color-filled contour maps, as well as the reflection peak shift speeds at different stages, even isomers such as n-butanol and iso-butanol, with a refractive index difference of only 0.001, can be recognized. The reflection peak shift speed depends on both the refractive index and the diffusion speed of chemicals. The proposed strategy provides a convenient, accurate, and low-cost method to detect vapors of homologues and isomers.