Silsesquioxane Core Research Articles

“Clicking” Amphiphilic Block Copolymers onto POSS Core: A General Approach for “Star-like” Polymers with Different Symmetry

“Star-like” macromolecules have been widely studied because of their unique physical and chemical properties, which play a great role in many important application fields. In this study, a library of star-like amphiphilic block copolymers consisting of a polyhedral oligomeric silsesquioxane (POSS) core and polyethylene glycol-bolck-polystyrene (PEGm-b-PSn) diblock copolymer arms with an exact arm number were prepared through a robust copper-catalysed azide-alkyne cycloadditions (CuAAC) and strain-promoted azide-alkyne cycloaddition (SPAAC) click reactions. Moreover, homo- and mikto-arms star polymers with different compositions were obtained by precisely regulating the central symmetry of the POSS core. The target polymers and intermediate products were characterized by nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), Fourier transform infrared (FT-IR) spectroscopy, and matrix-assisted laser desorption ionization time-of-flight (MALDI-ToF) mass spectrometry. This study demonstrates the chemical robustness of the novel POSS-based building block and establishes a general and efficient approach to prepare star-like macromolecules, especially for asymmetric heteroarm star-like macromolecules, which serve as important model compounds in the study of their bulk properties as well as self-assembling behaviors.

A flexible reverse-mode liquid crystal/polymer composite film with low driving voltage and high stability for energy-efficient smart windows

ABSTRACT Smart windows are attractive considering their contribution to energy efficiency and privacy protection. However, the achievement of flexible reverse-mode film with good stability and well electro-optical performance for smart windows remains a fascinating challenge in recent years. Herein, we reported a low-driving-voltage, high-stability flexible reverse-mode liquid crystal/polymer composite film for energy-efficient smart windows by the formation of polymer structure with a polyhedral oligomeric silsesquioxane (POSS) core and strong epoxy resin as chains. The experimental results suggested that the polymer can not only stabilise the planar state of the cholesteric liquid crystal in the zero field but also provide enough support to the continuous liquid crystal phase on flexible substrate. Besides, the optimised optical device could be fully driven at 30 V (lower than safety voltage, 36 V) and keep contrast ratio of 100. Moreover, the flexible film showed outstanding optical regulation performance and excellent cycle stability under electric field. The strategy used in this research would open new doors for the development of energy-efficient smart windows in buildings.

Synthesis of silsesquioxane-linked polyester with liquid crystalline backbone chain

A novel procedure for the synthesis of a 3D network polyester bearing silsesquioxane cores was executed to prepare the ternary silsesquioxane-linked copolyester BNH (BNH4 and BNH8) based on 4-acetoxy benzoic acid (ABA), 6-acetoxy-2-naphthoxylic acid (ANA), and a silsesquioxane-cored monomer (CSQ-AHA4 or CSQ-AHA8). The thermal data and phase behavior indicated that moderate crosslinking would reduce the stacking of the backbones, thereby enhancing the mobility of the backbone. However, greater crosslinking would limit the movement of the backbone, while the 3D cross-linked structure enhanced the structural stability of the phase region and the uniformity of the crystal size distribution. The loose fiber bundles showed that the participation of the 3D configuration and silsesquioxane increased the chain flexibility, and facilitated the formation of strong polyester ultrafine fibers. It was possible to improve the lateral mechanical properties of the oriented polyester materials, probably improving the mechanical properties aspect ratio of thin film materials.

Rationally Designed in-Situ Gelled Polymer-Ceramic Hybrid Electrolyte Enables Superior Performance and Stability in Quasi-Solid-State Lithium-Sulfur Batteries

Despite boasting giant leaps in performance improvement over the years, the current commercial standard, Li-ion batteries, are fast approaching their theoretical limits. Meanwhile, Lithium-Sulfur (Li-S) batteries offering ultra-high theoretical energy density (～2600 Whkg-1), cost-effectiveness, and nontoxicity are being seen as promising alternatives. Despite their plentiful advantages, the practicality of Li-S batteries has been largely stymied by several challenges: a) deleterious polysulfide dissolution and ‘shuttle effect’, b) significant volume change of S cathodes during cycling, c) safety concerns with flammable traditional glyme-based electrolyte, and d) the instability of Li anode. To mitigate these challenges, researchers have explored all-solid-state electrolytes, but their poor Li-ion conductivity, high interfacial impedance, and need for expensive, exotic materials and complex fabrication procedures severely limit their practical application.To overcome these challenges, we propose an in-situ gelled polymer-ceramic hybrid silsesquioxane-based electrolyte system. The gelled matrix, thermally crosslinked post cell fabrication, immobilizes the glyme-based liquid electrolyte and exhibits high liquid-like ionic conductivities (1.03 mS.cm-1), low interfacial impedance, and high oxidative potential (>4.5V vs. Li/Li+) . In this study, in addition to vastly decreased flammability, we report superior Li-ion conductivity compared to state-of-art solid-state Li-S electrolytes. This high ionic conductivity translated to a significantly improved specific capacity of 1050 mAh.gS-1 at 0.2 C, elevated Coulombic efficiencies (>98.5%), and elevated rate kinetics. The gelled electrolytes exhibited stable cycling in a large temperature range (-10oC - 60 oC). Moreover, polysulfide permeation studies and subsequent DFT calculations revealed that the gelled electrolyte exhibited strong chemical absorptivity to lithium polysulfides due to the polar silsesquioxane core, which translated to superior capacity retention (>80% over 200 cycles). Further, post- mortem XPS characterization studies revealed the formation of stable SEI at the anode and cathode, and SEM of cycled anodes showed reduced dendritic formations. Finally, the electrolyte was tested in practical pouch cell architecture, and the cells demonstrated excellent reliability even under mechanical stress. This work successfully reports a robust, rationally designed gelled electrolyte system for developing safe and high-performance quasi-solid state Li-S batteries.

Exploring Polyol-Functionalized Dendrimers with Silsesquioxane Cores.

Silsesquioxane dendrimers offer versatile structural potential, prompting our innovative synthesis of G1 and G2 polyol dendritic systems with diverse silsesquioxane cores, ranging from mono-T8 to difunctional and tetrafunctional double-decker silsesquioxanes. Through a strategic combination of hydrosilylation and O-silylation reactions, we have formed an extensive compound library. A major focus was directed toward investigating the reaction conditions of G1.5 dendrimers, as well as evaluating the stability and reactivity of the novel -O-Me2Si-H group. Notably, we unveiled solubility trends of these synthesized dendritic systems in basic organic solvents, offering vital information for potential applications. Our work advances dendrimer research by unraveling intricate synthesis, reactivity, and properties. We contribute to the broader understanding of these organic-inorganic complex interactions and envisage diverse applications in multiple domains.

Metallodendrimers Unveiled: Investigating the Formation and Features of Double-Decker Silsesquioxane-Based Silylferrocene Dendrimers.

Dendrimers exhibiting reversible redox properties have attracted extensive attention for their potential as electron transfer mediators, catalysts, and molecular sensors. In this study, we introduce intriguing G1 and G2 dendrimers featuring double-decker silsesquioxane cores and silylferrocene moieties. Through a carefully orchestrated sequence of condensation, reduction, and hydrosilylation reactions, these compounds were synthesized and comprehensively characterized spectroscopically and spectrometrically. Our investigation also encompassed the examination of their properties, including thermal stability, solubility in common organic solvents, and electrochemical behavior. We determined that these dendrimers possess the capability to form monolayers on platinum electrodes, which we conclusively demonstrated through the probing of cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy imaging. Notably, this study marks the first-ever example of modifying double-decker silsesquioxane cores with ferrocene groups while simultaneously representing one of the scarce instances of dendrimers exhibiting an open double-decker silsesquioxane core.

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.

Tricky but repeatable synthetic approach to branched, multifunctional silsesquioxane dendrimer derivatives

The efficient one-pot procedure based on a sequence of hydrosilylation and reduction reactions was applied to obtain carbosilane dendrimers with different silsesquioxane (SQ) cores,i.e.from mono-T8SQ, octa-T8SQ to di- and tetrafunctional double-decker silsesquioxanes.

Fully physically crosslinked POSS-based hydrogel with low swelling, high stretchable, self-healing, and conductive properties for human motion sensing

Conductive composite hydrogels are attracting much attention as artificial skin-like materials, with great potential for applications in wearable electronics, flexible printable electronics, and tissue engineering scaffolds. However, the design of conductive hydrogels possessing multifunctional properties such as excellent mechanical properties, self-healing, high conductivity, low swelling ratio (SR), and high strain sensitivity remains a challenge. Here, we designed and synthesized a polyhedral oligomeric silsesquioxane (POSS)-based composite hydrogel (OCAPS/PAA–Na/PAM) via the copolymerization of acrylamide and an ionic supramolecular monomer consisting of a cationic octa(3–chloroammoniumpropyl) silsesquioxane (OCAPS) core surrounded by sodium acrylate to achieve a combination of high stretchability, low SR, self-healing, high conductivity, biocompatibility, and strain sensing properties. The introduction of OCAPS as a physical crosslinking agent enhanced the toughness and compression properties of the hydrogel. The SR of the OCAPS/PAA–Na/PAM hydrogel was greatly suppressed, with a much lower value (SR: 200 %) than that of the hydrogel without POSS (SR: ~22,000 %). The elongation at break and fracture energy reached 4396 % and 3.7 kJ·m−2, respectively. OCAPS/PAA–Na/PAM hydrogels also had good self-healing properties due to the sufficient electrostatic interactions and hydrogen bonding between OCAPS and the polymer chains. Moreover, the supramolecular monomers provided abundant ion sites and in-situ generated NaCl, which imparted good electrical conductivity (0.678 mS·cm−1) and excellent strain sensitivity (gauge factor = 3.78) to the hydrogel. The OCAPS/PAA–Na/PAM hydrogel could detect electrical signal changes in large strain and small limb deformation and they showed good biological transmission sensitivity, which is expected to contribute to the fields of safety detection, gait detection, and wearable devices.

Synthesis of Functionalized Silsesquioxane Nanomaterials by Rhodium‐Catalyzed Carbene Insertion into Si−H Bonds

AbstractWe report carbene insertion into Si−H bonds of polyhedral oligomeric silsesquioxanes (POSS) for the synthesis of highly functionalized siloxane nanomaterials. Dirhodium(II) carboxylates catalyze insertion of aryl‐diazoacetates as carbene precursors to afford POSS structures containing both ester and aryl groups as orthogonal functional handles for further derivatization of POSS materials. Four diverse and structurally varied silsesquioxane core scaffolds with one, three, or eight Si−H bonds were evaluated with diazo reactants to produce a total of 20 new POSS compounds. Novel diazo compounds containing a fluorinated octyl group and boron‐dipyrromethene (BODIPY) chromophore demonstrate the use of highly functionalized substrates. Transformations of aryl(ester)‐functionalized POSS compounds derived from this method are demonstrated, including ester hydrolysis and Suzuki–Miyaura cross‐coupling.

Synthesis of Functionalized Silsesquioxane Nanomaterials by Rhodium-Catalyzed Carbene Insertion into Si-H Bonds.

We report carbene insertion into Si-H bonds of polyhedral oligomeric silsesquioxanes (POSS) for the synthesis of highly functionalized siloxane nanomaterials. Dirhodium(II) carboxylates catalyze insertion of aryl-diazoacetates as carbene precursors to afford POSS structures containing both ester and aryl groups as orthogonal functional handles for further derivatization of POSS materials. Four diverse and structurally varied silsesquioxane core scaffolds with one, three, or eight Si-H bonds were evaluated with diazo reactants to produce a total of 20 new POSS compounds. Novel diazo compounds containing a fluorinated octyl group and boron-dipyrromethene (BODIPY) chromophore demonstrate the use of highly functionalized substrates. Transformations of aryl(ester)-functionalized POSS compounds derived from this method are demonstrated, including ester hydrolysis and Suzuki-Miyaura cross-coupling.

Tadpole‐like Copolymer for Fabrication of Silica‐encapsulated Polysulfide Microspheres

AbstractA novel giant surfactant, possessing a well‐defined hydrophilic tail and a hydrophobic head with rigid multiple conjugate chains, tadpole‐like copolymer with polyhedral oligomeric silsesquioxane core (P9‐1), had been designed and synthesized via aminolysis/addition, interfacial oxidation polymerization. It was used to form complex micelles with polysulfides (PSL) for constructing the silica microspheres with micrometer dimensions in a simplified one‐pot synthesis. The characterization results for the morphologies of the complex micelles and the resulting microspheres indicated that the introduction of conjugated segments and steric hindrance of hybrid cage contributes to promote the stability and provide larger core space of the self‐assembled micelle to accommodate more PSL. With increasing the PSL/P9‐1 feed ratio, the size of microspheres and the content of PSL in the resulting microsphere were increased due to the PSL droplets providing a soft‐template for silica particles to build larger‐sized silica microspheres with PSL cores. And the growth mechanism of microstructures was also proposed in evaporation synthetic procedures, especially for special hollow morphology.

Effects of hetero‐armed star‐shaped PCL‐PLA polymers with POSS core on thermal, mechanical, and morphological properties of PLA

AbstractIn this study, AB type‐heteroarm star‐shaped poly(ε‐caprolactone)‐poly(lactic acid) (PCL‐PLA) polymers with polyhedral oligomeric silsesquioxane (POSS) core ((PCL)4‐POSS‐(PLA)4, coded as SPLA) were synthesized successfully by using ring opening polymerization and click chemistry techniques together. The synthesized polymers were compounded with commercial PLA at different blending ratios (PLA/SPLA = 100/0, 95/5, 90/10, and 80/20% wt). The effects of heteroarm SPLA polymers having different arm lengths (n = 10, 20, 30, and 50) on morphological, mechanical, and thermal behaviors of PLA were investigated. It is determined that SPLA polymers with four PLA and four PCL arms on its structure enhanced mechanical properties of PLA. The tensile modulus decreased, and lowest modulus values were observed with blends prepared at 80/20 ratio. Elongation at break values increased in all blends, maximum increment was observed with 1,4‐phenylene diisocyanate (PDI) containing SPLA20 blends prepared at 90/10 ratio. This result showed that SPLA20 had optimum chain length for chain extension reactions of between PLA chains. Besides, a trade compatibilizer PDI was utilized to enhance the intercompatibility of binary polymer blends.

Mixed star-shaped POSS-based molecule with hydroxy group-containing units and azobenzene fragments as two types of arms

Novel branched organic–inorganic nanoparticles with cubic octahedral silsesquioxane core containing the statistically grafted photoactive azobenzene fragments and 2-hydroxyethyl groups were synthesized via hydrosilylation coupling. Preservation of the photochromic properties of the reactants in the final product was revealed.

Zinc Imine Polyhedral Oligomeric Silsesquioxane as a Quattro-Site Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Low-Pressure CO2.

In the present research, the synthesis, spectroscopic characterization, and structural investigations of a unique ZnII complex of imine-functionalized polyhedral oligomeric silsesquioxane (POSS) is designed, and hereby described, as a catalyst for the synthesis of cyclic carbonates from epoxides and CO2. The uncommon features of the designed catalytic system is the elimination of the need for a high pressure of CO2 and the significant shortening of reaction times commonly associated with such difficult transformations like that of styrene oxide to styrene carbonate. Our studies have shown that imine-POSS is able to chelate metal ions like ZnII to form a unique coordination complex. The silsesquioxane core and the hindrance of the side arms (their steric effect) influence the construction process of the homoleptic Zn4@POSS-1 complex. The compound was characterized in solution by NMR (1H, 13C, 29Si), ESI-MS, UV/Vis spectroscopy and in the solid state by thermogravimetric/differential thermal analysis (TG-DTA), elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), cross-polarization magic angle spinning (CP MAS) NMR (13C, 29Si) spectroscopy, and X-ray crystallography.

In situ synthesis of star copolymers consisting of a polyhedral oligomeric silsesquioxane core and poly(2,5‐benzimidazole) arms for high‐temperature proton exchange membrane fuel cells

Star copolymers with good film-forming and mechanical properties were in situ synthesized for fabricating proton exchange membranes. The monomers of 3,4-diaminobenzoic acid were first grafted onto glycidyl-polyhedral oligomeric silsesquioxane (G-POSS) cores and then propagated to the poly(2,5-benzimidazole) (ABPBI) chains. The introduction of the star copolymer improves the movement of the ABPBI polymer chains, resulting in a lower internal viscosity and larger free volume that favor increased membrane flatness and absorbilities of water and phosphoric acid molecules, respectively. It was found that the star copolymers with 1.0 wt% of incorporated POSS (ABPBI-1.0POSS) had the best balance of the acid retentivity and film-forming property as well as mechanical properties that are desirable for proton exchange membranes without PA loss operating at high temperatures. The enhanced cell performance characteristics obtained using the ABPBI-1.0POSS-based membranes indicate that star copolymers are promising materials for use in high-temperature proton exchange membrane fuel cells.

Preparation of Tri(alkenyl)functional Open-Cage Silsesquioxanes as Specific Polymer Modifiers.

The scientific reports on polyhedral oligomeric silsesquioxanes are mostly focused on the formation of completely condensed T8 cubic type structures and recently so-called double-decker derivatives. Herein, we report on efficient synthetic routes leading to trifunctionalized, open-cage silsesquioxanes with alkenyl groups of varying chain lengths from -vinyl to -dec-9-enyl and two types of inert groups (iBu, Ph) at the silsesquioxane core. The presented methodology was focused on hydrolytic condensation reaction and it enabled obtaining titled compounds with high yields and purity. A parallel synthetic methodology that was based on the hydrosilylation reaction was also studied. Additionally, a thorough characterization of the obtained compounds was performed, also in terms of their thermal stability, melting and crystallization temperatures (TGA and DSC) in order to show the changes in the abovementioned parameters dependent on the type of reactive as well as inert groups at Si-O-Si core. The presence of unsaturated alkenyl groups has a profound impact on the application potential of these systems, i.e., as modifiers or comonomers for copolymerization reaction.

Silsesquioxane-Polythiophene Hybrid Copolymer as an Efficient Modifier for Single-Walled Carbon Nanotubes

One silsesquioxane-polythiophene hybrid copolymer, with combined star-like structure and intramolecular heterogeneity, was synthesized and sufficiently characterized via various methods, including FTIR, NMR, and SEC measurements. According to the exploration and characterization results, it was much more efficient at modifying SWNTs than its linear analogs in aqueous solution. The hydrophobic silsesquioxane core and PEDOT chains could locally anchor to the surface of the nanotubes, while the soluble flexible copolymer chains extended into the solution and rigid conjugated chains provided some π-π stacking effect to enhance adhesive force with the conjugated structure of the carbon nanotube, imparting steric stabilization to nanotube dispersion. The noncovalent interaction with SWNTs and solubility in aqueous solution improved the electrochemical characteristics of the modified-SWNT composite and availed for the preparation of a flexible and transparent electroactive film. Accordingly, this kind of silsesquioxane-polythiophene hybrid copolymer will be forwarded to apply to the assembling of flexible optoelectronic devices.

Luminescent Molecular Octopuses with a Polyhedral Oligomeric Silsesquioxane (POSS) Core and Iridium(III) Polypyridine Arms: Synthesis, Aggregation Induced Emission, Cellular Uptake, and Bioimaging Studies.

A new class of luminescent molecular hybrids in which eight cyclometalated iridium(III) polypyridine complexes are grafted onto a polyhedral oligomeric silsesquioxane (POSS) unit [POSS-{Ir(N^C)2 (py-im)}8 ](PF6 )8 [py-im=pyridine imine; HN^C=N-phenylpyrazole (Hppz) (1 a), 2-phenylpyridine (Hppy) (2 a), 2-phenylquinoline (Hpq) (3 a)] were synthesized and characterized. On photoexcitation, the complexes showed intense and long-lived orange-red to red emission in fluid solutions at room temperature and in low-temperature glasses. The photophysical properties including aggregation-induced emission and biological properties of these complexes were studied and compared with those of their POSS-free counterparts [Ir(N^C)2 (py-im)](PF6 ) [HN^C=Hppz (1 b), Hppy (2 b), Hpq (3 b)]. The (photo)cytotoxicity of the complexes was examined by the MTT assay, and their cellular uptake and intracellular localization were investigated by inductively coupled plasma-mass spectrometry and laser-scanning confocal microscopy.

OLIGOMERIC SILSESQUIOXANES COMBINING AZO- AND FLUORESCENT DYES IN ORGANIC SHELL

A method for the synthesis of reactive oligomeric silsesquioxanes, combining fragments of azo dye 4-(phenylazo)phenol and fluorescent dye Rhodamine B in various proportions in an organic shell was developed. These compounds were obtained by the reaction between the oligosilsesquioxane nanoparticles consisting of a mixture of linear, branched, ladder and polyhedral structures with epoxy groups in an organic frame (OSS–Ep) and the dyes. The structure of the synthesized substances was characterized by the methods of IR and 1H NMR spectroscopy. The UV-Vis spectra of OSS–Pp–Rh in DMF solution contain absorption bands characteristic of both acidic (560 and 350 nm) and lactone (in the range of 318–326 nm) forms of Rhodamine B. The absorption band of 4-(phenylazo) phenol fragments corresponding to π−π* transition is observed at 348 nm and overlaps the absorption band of Rhodamine B at 350 nm.The intensity of the absorption bands of fragments of various dyes depends on their content in organic frame of the silsesquioxane core. The intensity of the absorption bands at 348 nm and at 560 nm increases with an increase in the content of 4-(phenylazo)phenol and Rhodamine B correspondingly.It should be noted that when using DMF as a solvent the absorption band corresponding to acidic form of Rhodamine B at 560 nm in the UV-Vis spectra of the compounds obtained is more intense than similar band in the spectrum of the original Rhodamine B. Therefore, the attachment of Rhodamine B to the silsesquioxane core of oligomeric silsesquioxanes mixture does not have a significant effect on the position of absorption maxima in the UV-spectrum and prevents dye’s fragments from converting to the colorless lactone form. In the fluorescence spectra of OSS–Pp–Rh obtained using DMF as a solvent a peak at λ max = 592 nm (λex= 520 nm) is observed. The position of the fluorescence peak and its intensity in the spectra at the same optical density of the medium practically do not depend on the ratio of fragments of 4-(phenylazo)phenol and Rhodamine B in organic frame of OSS–Pp–Rh. The combination of two different chromophores in organic shell of the silsesquioxane core broadens the range of absorbed light and the change of their ratio allows to adjust the absorption intensity in a certain area. The presence of hydroxyl groups makes it possible to introduce the obtained compounds into the composition of polymeric organic-inorganic nanocomposites by covalent bonding.