Ionic Liquids Containing Silsesquioxane and Cyclic Siloxane Frameworks

This paper describes the author's recent work on the preparation and properties of thermally stable ionic liquids (ILs) containing siloxane frameworks. Quaternary ammonium and imidazolium salt-type ILs containing random oligosilsesquioxane frameworks were successfully prepared via the hydrolytic condensation of the corresponding organotrialkoxysilanes by using an aqueous superacid bis(trifluoromethanesulfonyl)imide (HNTf2 ) solution as a catalyst and solvent. Imidazolium salt-type ILs containing polyhedral oligomeric silsesquioxane (POSS) frameworks were also prepared through a reaction similar to that described above by using a water/methanol mixed solution of HNTf2 . In addition, amorphous POSSs with two types of ionic groups randomly distributed in the side chain were prepared. These POSSs were ILs exhibiting fluidity at relatively low temperatures. Furthermore, imidazolium and ammonium salt-type ILs containing cyclic oligosiloxane frameworks were prepared through a reaction similar to that of the corresponding organodialkoxysilanes. The thermal decomposition temperatures of the above ILs containing siloxane frameworks were higher than those of general ILs.

Novel hybrid composites based on double-decker silsesquioxanes functionalized by methacrylate derivatives and polyvinyl alcohol as potential materials utilized in biomedical applications

The use of diverse biomaterials for regenerative medicine is constantly evolving. Therefore, looking for easy-to-scale-up materials in terms of preparation, less complex composition, and featuring structural and chemical stability seems justified. In this work, we report the preparation of double-decker silsesquioxane-based (DDSQ-based) composites, which, according to our best knowledge, have never been used as biomaterials. A family of methacrylate-substituted DDSQs was obtained starting from the previously reported hydroxyalkyl double-decker silsesquioxanes. In the resulting hybrids, methacrylate groups are attached to each other's lateral silicon atoms of DDSQ in trans positions, providing an excellent geometry for forming thin layers. In contrast to pure organic methacrylates, the covalent bonding of methacrylate derivatives to inorganic silsesquioxane core improves mechanics, cell adhesion, and migration properties. Furthermore, to increase the hydrophilicity of the resulting DDSQ-based hybrids, polyvinyl alcohol (PVA) was added. The entire system forms an easy-to-obtain two-component (DDSQ-PVA) composite, which was subjected without any upgrading additives to biological tests later in the research. The resulting biomaterials fulfill the requirements for potential medical applications. Human fibroblasts growing on prepared hybrid composites are characterized by proper spindle-shaped morphology, proliferation, and activation status similar to control conditions (cells cultured on PVA), as well as increased adhesion and migration abilities. The obtained results suggest that the prepared biomaterials may be used in regenerative medicine in the future.

Cage-like silsesquioxanes-based hybrid materials

Cage-like silsesquioxanes are considered to be ideal and versatile building blocks of hybrid materials due to their unique structures and excellent performance. This Perspective highlights recent advances in the field of cage-like silsesquioxane-based hybrid materials, ranging from monomer functionalization and materials preparation to application. The existing issues are reviewed and the challenges and prospects in this field are also discussed for further development and exploitation.

Control of Crystalline-Amorphous Structures of Polyhedral Oligomeric Silsesquioxanes Containing Two Types of Ammonium Side-Chain Groups and Their Properties as Protic Ionic Liquids

Polyhedral oligomeric silsesquioxanes (POSSs), Am-POSS(x,y), prepared by hydrolytic condensation, contains two types of ammonium side-chain groups, where the numbering of x and y represents the type of ammonium ions in the POSS structure, corresponding to primary (1), secondary (2), tertiary (3), and quaternary (4) ammonium ions. Mixtures of the two starting materials selected from organotrialkoxysilanes containing primary, secondary, and tertiary amines and a quaternary ammonium salt [(RO)₃Si(CH₂)₃R′, R = CH₃ or CH₂CH₃, R′ = NH₂, NHCH₃, N(CH₃)₂, and N(CH₃)₃Cl] were dissolved in dimethyl sulfoxide (DMSO). The hydrolytic condensation was performed in the presence of bis(trifluoromethansulfonyl)imide (HNTf₂) and water. All Am-POSS(x,y) structures consisted of a cage-type octamer (T₈-POSS), as confirmed by ²⁹Si NMR spectrometry and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses indicated that Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) had amorphous structures. These POSSs have two or three differences in the number of methyl groups between the two types of ammonium side-chains. Conversely, Am-POSS(1,2), Am-POSS(2,3), and Am-POSS(3,4) had crystalline structures. The difference in the number of methyl groups between the two types of ammonium side-chains in these POSSs is only one. Therefore, the crystalline-amorphous structure of Am-POSS(x,y) is controlled by the side-chain group combinations. Furthermore, Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) are protic ionic liquids with relatively low flow temperatures.

New Polyhedral Oligomeric Silsesquioxanes-Based Fluorescent Ionic Liquids: Synthesis, Self-Assembly and Application in Sensors for Detecting Nitroaromatic Explosives

In this paper, two different models of hybrid ionic liquids (ILs) based on polyhedral oligomeric silsesquioxanes (POSSs) have been prepared. Additionally, these ILs based on POSSs (ILs-POSSs) exhibited excellent thermal stabilities and low glass transition temperatures. ¹H, 13C, and 29Si nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to confirm the structures of the IL-POSSs. Furthermore, the spherical vesicle structures of two IL-POSSs were observed and were caused by self-assembly behaviors. In addition, we found it very meaningful that these two ILs showed lower detection limits of 2.57 × 10-6 and 3.98 × 10-6 mol/L for detecting picric acid (PA). Moreover, the experimental data revealed that the products have high sensitivity for detecting a series of nitroaromatic compounds-including 4-nitrophenol, 2,4-dinitrophenol, and PA-and relatively comprehensive explosive detection in all of the tests of IL-POSSs with nitroaromatic compounds thus far. Additionally, the data indicate that these two new ILs have great potential for the detection of explosives. Therefore, our work may provide new materials including ILs as fluorescent sensors in detecting nitroaromatic explosives.

Increasing Photovoltaic Performance of an Organic Cationic Chromophore by Anion Exchange

A symmetrical cyanine dye chromophore is modified with different counteranions to study the effect on crystal packing, polarizability, thermal stability, optical properties, light absorbing layer morphology, and organic photovoltaic (OPV) device parameters. Four sulfonate-based anions and the bulky bistriflylimide anion are introduced to the 2-[5-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-1,3-pentadien-1-yl]-1,3,3-trimethyl-3H-indolium chromophore using an Amberlyst A26 (OH^- form) anion exchanger. Anionic charge distribution clearly correlates with device performance, whereby an average efficiency of 2% was reached in a standard bilayer organic solar. Evidence is given that the negative charge of the anion distributed over a large number of atoms is significantly more important than the size of the organic moieties of the sulfonate charge carrying group. This provides a clear strategy for future design of more efficient cyanine dyes for OPV applications.

Preparation of protic ionic liquids containing cyclic oligosiloxane frameworks

Protic ionic liquids containing cyclic oligosiloxane frameworks, which were prepared by the hydrolytic condensation method, exhibited relatively high thermal stabilities.

Architecture, Assembly, and Emerging Applications of Branched Functional Polyelectrolytes and Poly(ionic liquid)s

Branched polyelectrolytes with cylindrical brush, dendritic, hyperbranched, grafted, and star architectures bearing ionizable functional groups possess complex and unique assembly behavior in solution at surfaces and interfaces as compared to their linear counterparts. This review summarizes the recent developments in the introduction of various architectures and understanding of the assembly behavior of branched polyelectrolytes with a focus on functional polyelectrolytes and poly(ionic liquid)s with responsive properties. The branched polyelectrolytes and poly(ionic liquid)s interact electrostatically with small molecules, linear polyelectrolytes, or other branched polyelectrolytes to form assemblies of hybrid nanoparticles, multilayer thin films, responsive microcapsules, and ion-conductive membranes. The branched structures lead to unconventional assemblies and complex hierarchical structures with responsive properties as summarized in this review. Finally, we discuss prospectives for emerging applications of branched polyelectrolytes and poly(ionic liquid)s for energy harvesting and storage, controlled delivery, chemical microreactors, adaptive surfaces, and ion-exchange membranes.

Construction of porous cationic frameworks by crosslinking polyhedral oligomeric silsesquioxane units with N-heterocyclic linkers

In fields of materials science and chemistry, ionic-type porous materials attract increasing attention due to significant ion-exchanging capacity for accessing diversified applications. Facing the fact that porous cationic materials with robust and stable frameworks are very rare, novel tactics that can create new type members are highly desired. Here we report the first family of polyhedral oligomeric silsesquioxane (POSS) based porous cationic frameworks (PCIF-n) with enriched poly(ionic liquid)-like cationic structures, tunable mesoporosities, high surface areas (up to 1,025 m(2) g(-1)) and large pore volumes (up to 0.90 cm(3) g(-1)). Our strategy is designing the new rigid POSS unit of octakis(chloromethyl)silsesquioxane and reacting it with the rigid N-heterocyclic cross-linkers (typically 4,4'-bipyridine) for preparing the desired porous cationic frameworks. The PCIF-n materials possess large surface area, hydrophobic and special anion-exchanging property, and thus are used as the supports for loading guest species PMo10V2O40(5-); the resultant hybrid behaves as an efficient heterogeneous catalyst for aerobic oxidation of benzene and H2O2-mediated oxidation of cyclohexane.

A polyhedral oligomeric silsesquioxane-based catalyst for the efficient synthesis of cyclic carbonates

Polyhedral oligomeric silsesquioxane functionalized with imidazolium chloride peripheries was synthesized and successfully used as a catalyst for CO₂ conversion.