Synthesis of poly(siloxane/double-decker silsesquioxane) via dehydrocarbonative condensation reaction and its functionalization

Tris(pentafluorophenyl)borane-catalyzed Hydride Transfer Reactions in Polysiloxane Chemistry-Piers-Rubinsztajn Reaction and Related Processes

Tris(pentafluorophenyl)borane (TPFPB) is a unique Lewis acid that catalyzes the condensation between hydrosilanes (Si-H) and alkoxysilanes (Si-OR), leading to the formation of siloxane bonds (Si-OSi) with the release of hydrocarbon (R-H) as a byproduct-the so-called Piers-Rubinsztajn reaction. The analogous reactions of hydrosilanes with silanols (Si-OH), alcohols (R-OH), ethers (R-OR') or water in the presence of TPFPB leads to the formation of a siloxane bond, alkoxysilane (Si-OR or Si-OR') or silanol (Si-OH), respectively. The above processes, often referred to as Piers-Rubinsztajn reactions, provide new synthetic tools for the controlled synthesis of siloxane materials under mild conditions with high yields. The common feature of these reactions is the TPFPB-mediated hydride transfer from silicon to carbon or hydrogen. This review presents a summary of 20 years of research efforts related to this field, with a focus on new synthetic methodologies leading to numerous previously difficult to synthesize well-defined siloxane oligomers, polymers and copolymers of a complex structure and potential applications of these new materials. In addition, the mechanistic aspects of the recently discovered reactions involving hydride transfer from silicon to silicon are discussed in more detail.

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.

Construction of Fluorescent Conjugated Polytriazole Containing Double-Decker Silsesquioxane: Click Polymerization and Thermal Stability

This study synthesized two azide-functionalized monomers through p-dichloro xylene and double-decker silsesquioxane (DDSQ) units with NaN₃ to form DB-N₃ and DDSQ-N₃ monomers, respectively. In addition, five different propargyl-functionalized monomers were also prepared from hydroquinone, bisphenol A, bis(4-hydroxyphenyl)methanone, 2,4-dihydroxybenzaldehyde (then reacted with hydrazine hydrate solution) and 1,2-bis(4-hydroxyphenyl)-1,2-diphenylethene with propargyl bromide to form P-B, P-BPA, P-CO, P-NP, and P-TPE monomers, respectively. As a result, various DDSQ-based main chain copolymers could be synthesized using Cu(I)-catalyzed click polymerization through DDSQ-N₃ with different propargyl-functionalized monomers, of which the chemical structure and molecular weight could be confirmed by using Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC) analyses. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy analyses also could characterize the thermal stability, morphology, and optical behaviors of these DDSQ-based copolymers. All results indicate that the incorporation of an inorganic DDSQ cage could improve the thermal stability such as thermal decomposition temperature and char yield, because of the DDSQ dispersion homogeneously in the copolymer matrix, and this would then affect the optical properties of NP and TPE units in this work.

Distinct insight into the use of difunctional double-decker silsesquioxanes as building blocks for alternating A–B type macromolecular frameworks

A distinct look at known, hydrosilylation reactions used for the formation of DDSQ-based linear A–B alternating macromolecular systems with DPn > 1000 is presented. Selected physicochemical properties of obtained hybrid co-polymers were determined.

Hydroxyalkyl-substituted double-decker silsesquioxanes: effective separation of cis and trans isomers

A procedure to sequentially crystallize the two isomers of hydroxyalkyl-substituted double-decker silsesquioxanes from one another, which may result in the preparation of new materials and polymers with well-defined properties, is reported.

Double-Decker Silsesquioxanes Self-Assembled in One-Dimensional Coordination Polymeric Nanofibers with Emission Properties

The urgent needs for photoactive materials in industry drive fast evolution of synthetic procedures in many branches of chemistry, including the chemistry of silsesquioxanes. Here, we disclose an effective protocol for the synthesis of novel double-decker silsesquioxanes decorated with two (styrylethynylphenyl)terpyridine moieties (DDSQ_Ta-b). The synthesis strategy involves a series of silylative and Sonogashira coupling reactions and is reported for the first time. DDSQ_Ta-b were employed as nanocage ligands to promote self-assembly in the presence of transition metals (TM), i.e., Zn2+, Fe2+, and Eu3+ ions, to form one-dimensional (1D) coordination polymeric nanofibers. Additionally, ultraviolet-promoted and reversible E-Z isomerization of the C═C bond within the ligand structures may be exploited to tune their emission properties. These findings render such complexes promising candidates for applications in materials chemistry. This is the first example of 1D coordination polymers bearing DDSQ-based nodes with TM ions.

Vinyl-Functionalized Janus Ring Siloxane: Potential Precursors to Hybrid Functional Materials

A vinyl-functionalized all-cis-tetrasiloxycyclotetrasiloxane [ViSi(OSiMe2H)O]4 (Vi = vinyl group) Janus precursor was prepared from potassium cyclotetrasiloxane silanolate. The Janus precursor was selectively modified at its dimethylhydrosilyl groups [-SiMe2H] via the Piers-Rubinsztajn reaction to obtain a family of new tetravinyl-substituted Janus rings [ViSi(OR')O]4 containing various functional groups in moderate yields. Remarkably, the tetravinyl groups on the structure remained intact after modification by the Piers-Rubinsztajn reaction. Since these synthesized compounds possess multiple functional groups (up to eight per molecule), they are potential precursors for advanced hybrid organic-inorganic functional materials.

Identifying and mapping chemical bonding within phenolic resin using secondary electron hyperspectral imaging

“Secondary electron hyperspectral imaging (SEHI) is an innovative SEM-based analysis tool allowing spatially-resolved chemical analysis beyond elemental composition”.

Well-defined hydrogen and organofunctional polysiloxanes with spiro-fused siloxane backbones

Structurally well-defined macrocyclic polysiloxanes with unique spirosiloxane units and regularly arranged Si–H groups were synthesized by B(C₆F₅)₃-catalyzed dehydrocarbonative cross-couplings.

Organocatalytic controlled/living ring-opening polymerization of 1,3,5-triphenyl-1,3,5-tri-p-tolylcyclotrisiloxane for the precise synthesis of fusible, soluble, functionalized, and solid poly[phenyl(p-tolyl)siloxane]s

An organocatalytic controlled/living ring-opening polymerization (ROP) of 1,3,5-triphenyl-1,3,5-tri(p-tolyl)cyclotrisiloxane (PT3) produced linear poly[phenyl(p-tolyl)siloxane] (PPTS) with controlled structures.

Symmetry driven: the synthesis of co-substituent octasilsesquioxanes

Cubic octasilsesquioxanes with mixed substituents were directly synthesized through a sol–gel process using the mixture of i-butyl(triethoxysilane) and other alkoxysilanes.

Polyphenylsilsesquioxanes. New structures-new properties

The review describes the synthesis and properties of various forms of polyphenylsilsesquioxane (PPSQ). Among the forms described, we present the well-known ladder (l-PPSQ) and polyhedral (p-PPSQ) forms, from the first studies to the latest achievements. The practical prospects of these compounds and the possibility of their modification are estimated. These PPSQ have a regular polycyclic structure, which allowed us to compare them with random polycyclic analogs (r-PPSQ). The last part of the review describes the acyclic PPSQ (a-PPSQ) obtained recently. The methods for their synthesis and modification are presented. Modification of (a-PPSQ) allows two new forms of PPSQ to be obtained. The first one is a hyperbranched PPSQ. The second one is a globular PPSQ or a nanogel as it is called by the authors. Both forms are of great interest because their physicochemical properties differ greatly from the known ones (l-PPSQ, p-PPSQ, r-PPSQ). The areas of practical application of the new PPSQ forms are predicted.

The review describes the synthesis and properties of various forms of polyphenylsilsesquioxane (PPSQ).

Characteristics of Thermosetting Polymer Nanocomposites: Siloxane-Imide-Containing Benzoxazine with Silsesquioxane Epoxy Resins

A series of innovative thermosetting polymer nanocomposites comprising of polysiloxane-imide-containing benzoxazine (PSiBZ) as the matrix and double-decker silsesquioxane (DDSQ) epoxy or polyhedral oligomeric silsesquioxane (POSS) epoxy were prepared for improving thermosetting performance. Thermomechanical and dynamic mechanical characterizations indicated that both DDSQ and POSS could effectively lower the coefficient of thermal expansion by up to approximately 34% and considerably increase the storage modulus (up to 183%). Therefore, DDSQ and POSS are promising materials for low-stress encapsulation for electronic packaging applications.

Janus ring siloxane: a versatile precursor of the extended Janus ring and tricyclic laddersiloxanes

All-cis-tetrasiloxycyclotetrasiloxanes (Janus ring siloxanes) were facilely prepared from all-cis-cyclotetrasiloxanetetraol or sodium cyclotetrasiloxane silanolates. Moreover, we demonstrated the synthesis of extended Janus rings, [RSi(OR')O]4, containing various functional groups, via the Piers-Rubinsztajn reaction using a Janus ring siloxane as a precursor. Remarkably, we discovered the formation of an unexpected all-cis tricyclic laddersiloxane as a by-product. These synthesized compounds can be potential monomers of well-defined cage silsesquioxanes, Janus-type nanomaterials, and porous materials.

Synthesis of Tetrachloro, Tetraiodo, and Tetraazido Double-Decker Siloxanes

A convenient and scalable (gram-scale) route to unprecedented T₈D₂-double-decker siloxanes (DDSQs) bearing four chloro (3b) or four azido (5b) groups is reported. Both compounds were characterized and proved to undergo successful nucleophilic substitution for 3b (with iodide or azide) and copper-catalyzed azide-alkyne [3 + 2] cycloaddition for 5b. All of these transformations occurred under mild conditions, and the corresponding DDSQs were prepared in very high yields. Beyond the enhanced multivalency as compared to the previously described disubstituted D₂T₈ structures, the reported tetrafunctional DDSQs are formed as a single isomer and readily isolated in very high yields. Moreover, the tetra-azido DDSQ 5b constitutes a multipurpose nanobuilding block for the further preparation of new inorganic-organic hybrid materials where the covalent incorporation of a DDSQ moiety brings valuable properties.

Progress in the Synthesis of Bifunctionalized Polyhedral Oligomeric Silsesquioxane

Polyhedral oligomeric silsesquioxane (POSS) has been considered as one of the most promising nanofillers in academic and industrial research due to its unique multifunctional nanostructure, easy functionalization, hybrid nature, and high processability. The progress of POSS has been extensive, particularly applications based on single- or multiple-armed POSS. In polymer hybrids, in order to enhance the properties, bifunctional POSS has been incorporated into the backbone chain of the polymer. This review summarizes recent developments in the synthesis, modification, and application of bifunctional POSS-containing composite materials. This includes amino-POSS, hydroxyl-POSS, aromatic ring-POSS, ether-POSS, and vinyl groups-POSS and their applications, exemplified by polyurethanes (PUs) and polyimides (PIs). In addition, the review highlights the enhancement of thermal, mechanical, and optical properties of the composites.

Synthesis of a "Butterfly Cage" Based on a Double-Decker Silsesquioxane

Novel polyhedral structures were prepared with a butterfly-shape composed of oligosiloxane wings and a double-decker silsesquioxane (DDSQ) body. The compounds were synthesized in two steps from commercially available alkoxysilanes, and their structures were confirmed using spectroscopic methods and X-ray crystallography. Not like other phenyl-substituted cage silsesquioxanes, these butterfly cages show very good solubility in common organic solvents. The crystal structures clearly showed their unique features: a larger space with longer siloxane chains and a very flexible framework. Moreover, these compounds are thermally stable with a Td₅ (5 % weight loss temperature) over 320 °C.

Synthesis and Characterization of Unsymmetrical Double-Decker Siloxane (Basket Cage)

The one-pot synthesis of an unsymmetrical double-decker siloxane with a novel structure via the reaction of double-decker tetrasodiumsilanolate with 1 equiv. of dichlorotetraphenyldisiloxane in the presence of an acid is reported herein for the first time. The target compound bearing all phenyl substituents on the unsymmetrical siloxane structure was successfully obtained, as confirmed by ¹H-NMR, ¹³C-NMR, ²⁹Si-NMR, IR, MALDI-TOF, and X-ray crystallography analyses. Additionally, the thermal properties of the product were evaluated by TG/DTA and compared with those of other siloxane cage compounds.

Synthesis of structured polysiloxazanes via a Piers-Rubinsztajn reaction

A series of siloxazanes were successfully prepared by a Piers-Rubinsztajn reaction between methoxydisilazanes and the corresponding hydrosilanes. Polysiloxazanes with narrow dispersion were also synthesized from methoxydisilazanes and Si-H terminated oligosiloxanes. The possible interaction mechanism between tris(pentafluorophenyl)borane and the methoxydisilazane was investigated.

Caterpillar-shaped polysilsesquioxanes

The preparation of linear polysilsesquioxanes having Si-OH side groups is not trivial, because direct condensation of multifunctional silanol derivatives would lead to branched or crosslinked polymers. We have successfully prepared an unsymmetrical double-decker silsesquioxane with a silyl hydride function at one end and two silanol groups at the other. Linear POSS polymers having Si-OH side groups are obtained selectively in good yields. The properties and potential applications are briefly presented.

Synthesis of Structurally Precise Polysiloxanes via the Piers⁻Rubinsztajn Reaction

Silicone materials are widely used, from daily life to the military industry. With the advancement of science and technology and the increasing demands of industry, the requirement for high-performance precise structural silicone materials has increased. Therefore, the most important aspect in this field is finding a breakthrough in the synthetic methods. In this review, the latest research developments in controllable morphological structure and composite structure optimized synthesis of silicone materials using the Piers⁻Rubinsztajn (PR) reaction are summarized. The advantages of the PR reaction compared with traditional synthetic routes to silicone materials are presented. The highly controllable spatial structure of silicone materials and the structural combination of biomass or inorganic materials with silicone materials results in an improvement in performance or function. The morphological control of more complex silicone materials and the synthesis of non-traditional silicone materials with composite structures through the PR reaction will be the main research directions for the development of silicone materials in the future.

Research status, industrial application demand and prospects of phenolic resin

The synthesis process of the phenolic resin adhesive was developed in the 19th century, and its excellent environmental resistance and high bonding strength make it one of the main wood adhesives. With the development of industry, phenolic resin adhesive is not only used in plywood, wood processing and laminate, but also in automobile, aerospace, composite materials and other fields. Herein we review the main synthetic processes and latest research progress for phenolic resin adhesives, the capacity distribution of major domestic phenolic resin enterprises, analysis of domestic phenolic resin consumption, import and export volume and price, Chinese plywood production, and the main production and export markets. Furthermore, research and discussion on the commercial application of domestic phenolic resin adhesives in plywood were carried out, which provides a reference for development of better phenolic resin adhesives that meet the development needs of the country, along with quality and economic competitiveness.

The synthesis process of the phenolic resin adhesive was developed in the 19th century, and its excellent environmental resistance and high bonding strength make it one of the main wood adhesives.

Anion identification using silsesquioxane cages

Anthracene-conjugated octameric silsesquioxane cages thermodynamically display intramolecular excimer formation, which can be used to identify anions through the change of fluorescence.

Anthracene-conjugated octameric silsesquioxane (AnSQ) cages, prepared via Heck coupling between octavinylsilsesquioxane (OVS) and 9-bromoanthracene, thermodynamically display intramolecular excimer emissions. More importantly, these hosts are sensitive to each anionic guest, thereby resulting in change of anthracene excimer formation, displaying the solvent-dependent fluorescence and allowing us to distinguish up to four ions such as F^–, OH^–, CN^– and PO₄^3– by fluorescence spectroscopy. Depending on the solvent polarity, for example, both F^– and CN^– quenched the fluorescence emission intensity in THF, but only F^– could enhance the fluorescence in all other solvents. The presence of PO₄^3– results in fluorescence enhancements in high polarity solvents such as DMSO, DMF, and acetone, while OH^– induces enhancements only in low polarity solvents (e.g. DCM and toluene). A picture of the anion recognizing ability of AnSQ was obtained through principal component analysis (PCA) with NMR and FTIR confirming the presence of host–guest interactions. Computational modeling studies demonstrate the conformation of host–guest complexation and also the change of excimer formation. Detection of F^–, CN^– and OH^– by AnSQ hosts in THF is noticeable with the naked eye, as indicated by strong color changes arising from charge transfer complex formation upon anion addition.

Tunable Porosity of Cross-Linked-Polyhedral Oligomeric Silsesquioxane Supports for Palladium-Catalyzed Aerobic Alcohol Oxidation in Water

Polyhedral oligomeric silsesquioxane (POSS)-based materials, poly-POSS-T_n [n = 8 (1), 10 (2), 12 (3), and mix (4)], were prepared in high yields via free radical polymerization of corresponding pure forms of methacrylate-functionalized POSS monomers, MMA-POSS-T_n (n = 8, 10, 12), and the mixture form, MMA-POSS-T_mix. Powder X-ray diffraction (XRD) spectra and BET analysis indicate that 1-4 are amorphous materials with high surface areas (683-839 m² g^-1). The surface areas and total pore volumes follow the trend: poly-POSS-T₁₂ > poly-POSS-T₁₀ > poly-POSS-T_mix > poly-POSS-T₈. In addition, on the basis of Barrett-Joyner-Halenda (BJH) analysis, poly-POSS-T₁₂ contains the highest amount of mesopores. The Pd nanoparticles immobilized on poly-POSS-T_n [n = 8 (5), 10 (6), 12 (7), and mix (8)] are well dispersed with 4-6 wt % Pd content and similar average particle sizes of 6.2-6.5 nm, according to transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDX) and microwave plasma-atomic emission spectroscopy (MP-AES). At 90 °C, the stabilized Pd nanoparticles in 5-8 catalyzed aerobic oxidation of benzyl alcohol to benzaldehyde in 72-100% yields at 6 h using a mixture of a H₂O/Pluronic (P123) solution. The PdNp@poly-POSS-T₈ catalyst (5) exhibited the lowest catalytic activity, as a result of its lowest surface areas, total pore volumes, and amounts of mesopores. With the catalyst 8, various benzyl alcohol derivatives were converted to the corresponding aldehydes in good to excellent yields. However, with alcoholic substrates featuring electron-withdrawing substituents, high conversions were achieved with 1 equiv of K₂CO₃ additive and longer reaction times.

Targeted design of water-based humic substances-silsesquioxane soft materials for nature-inspired remedial applications

Water-based humic substances-silsesquioxane (HS-SQ) soft materials are synthesized by hydrolysis of (3-aminopropyl-triethoxy)-silane in the HS solution, ​immobilized onto sand columns, and used for intercepting azo dye from water.

Interaction of organodialkoxysilanolates with carbon dioxide

A series of organo(alkoxy)disiloxanes was obtained by the reaction of CO₂with sodium alkoxy(organo)silanolates under high pressure. It is suggested that the reaction involves intermediate formation of the carbonate derivative of sodium alkoxy(organo)silanolates.