X-ray Crystal Structures, Packing Behavior, and Thermal Stability Studies of a Homologous Series of n-Alkyl-Substituted Polyhedral Oligomeric Silsesquioxanes

Synthesis of a series of octaalkoxy-substituted cage silsesquioxanes catalyzed by zinc acetate

Octaalkoxy-substituted polyhedral oligomeric silsesquioxane (8RO-POSS) is an attractive starting material for producing silicone resins. However, polymers derived from 8RO-POSS via the sol-gel process have seldom been reported owing to their synthetic difficulty. In this study, we attempted to use zinc acetate (Zn(OAc)2) as the catalyst for the synthesis of a series of 8RO-POSS from octahydrido-POSS (8H-POSS). The reaction conditions were optimized using heptaisobutyl monohydride-POSS (7iBu1H-POSS) as a model reaction. The desired product was obtained in 96% yield under optimized conditions. The alkoxylation of 8H-POSS was performed using methanol (MeOH), ethanol (EtOH), isopropyl alcohol (i-PrOH), and tert-butyl alcohol (t-BuOH) in the presence of Zn(OAc)2 as the catalyst. Although octamethoxy-POSS (8MeO-POSS) was isolated in the presence of a byproduct, octaethoxy-POSS (8EtO-POSS) and octaisopropoxy-POSS (8iPrO-POSS) were obtained in high yields. The degree of alkoxylation was 55% in the case of using t-BuOH. The structures of 8MeO-POSS, 8EtO-POSS, and 8iPrO-POSS were confirmed by FT-IR, 1H-, and 29Si-NMR and MALDI-TOF-MS analyses. Compared to the random silicate obtained by base-treated tetramethoxysilane (TMOS), base-treated 8EtO-POSS and 8iPrO-POSS showed that the cage structures were maintained even after the formation of condensed silicate structures via a condensation reaction.

Fast proton conductors for low humidity: hydrophilic sulfonated and phosphonated polysilsesquioxanes with Al-O-P crosslinks

Proton-conducting polysilsesquioxane oligomers with core-shell structures consisting of hydrophilic silica-rich cores surrounded by an organic layer with sulfonic and phosphonic acid groups were synthesized. They were crosslinked by mixing with phosphoric acid and aluminum ions to form a hydrophilic Al-O-P framework. The resulting polymers were clear, uniform, flexible, and exhibited a high proton conductivity above 100 °C in non-humidified low-humidity air (∼22 mS cm-1 at 120 °C and ∼1%RH) because of their high sulfonic acid concentration and high water retention capability.

Influence of Substitutional Groups on the Ordering and Crystallization of Amphiphilic Silsesquioxanes at the Air-Water Interface

We report on the surface ordering and crystallization sequences in differently organic-substituted amphiphilic polyhedral silsesquioxane (POSS) variants induced by regulated compression at the air-water interface. Such molecular systems floating at the interface serve as a model system to study dynamic crystallization mediated by weak interactions. In situ grazing incidence X-ray scattering (GIXS) measurements, performed at a synchrotron X-ray source using a liquid surface diffractometer and corroborated with Brewster angle microscopy, revealed transformations for the different POSS variants (viz. trisilanol isobutyl POSS (TBPOSS), trisilanol cyclohexyl POSS (TCHPOSS), disilanol octaisobutly POSS (DOBPOSS), and trisilanol isooctyl POSS (TOPOSS)) from a weakly correlated monolayer structure to appreciably different structural and crystalline phases in various packing schemes. GIXS measurements revealed a stable nature of the crystallization of DOBPOSS, varying degrees of metastable crystallization for TCHPOSS and TBPOSS, and complete absence of crystalline phase in TOPOSS molecules. Incidentally, for all POSS variants showing crystalline phases, the motifs always assembled in a triclinic lattice with P1̅ symmetry. For the metastable crystals, preferential surface ordering of the crystallites promotes selective crystalline planes to exhibit preferred tilt angles with respect to the interface. The structural transformations of the differently substituted POSS molecules and their variations therein are attributed to the changing balance of the hydrophobic vs hydrophilic interaction in the layers, which is determined by the anisotropic shape and distribution of substitutional groups over the nanosized core cage of the monomer, steric interaction between nearest dimeric neighbors, as well as the in-plane and out-of-plane assembly of the overlayers.

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.

Dialkenylgermanes as Precursors of Silsesquioxane-based Macromolecular Structures

Herein we report a study of highly efficient platinum-catalyzed hydrosilylation of dialkenylgermanes with silsesquioxanes and spherosilicates. The use of divinyl- and diallylgermanes allowed the synthesis of new classes of compounds, i. e., dumbbell-type systems, silsesquioxanes with alkenyl pendant group, and oligomeric derivatives. The results are supported by detailed data from in situ FT-IR and NMR measurements, enabling precise monitoring of the reaction progress and determination of regioselectivity of the formed products.

Introduction of organogermyl functionalities to cage silsesquioxanes

In this work, we present the first example of highly efficient platinum-catalyzed hydrosilylation of vinyl- and allylgermanes with different types of silsesquioxanes and spherosilicates. This protocol allows the straightforward introduction of organogermyl functionalities with alkyl chains linked to the silsesquioxane core with good yields and excellent selectivity. These derivatives may be applied as precursors for the development of advanced hybrid materials in the future. In addition, a comparison made between vinylsilanes and vinylgermanes showed a higher reactivity of germanium compounds in the hydrosilylation reaction. To the best of our knowledge, this is the first literature example of the functionalization of silsesquioxanes and spherosilicates with these types of germanium derivatives. The reaction parameters and kinetics were determined by in situ FT-IR. In addition, our research is supported by extensive data obtained from NMR measurements.

Self-assembly of fluoride-encapsulated polyhedral oligomeric silsesquioxane (POSS) nanocrystals

The self-assembly and crystal packing of a unique series of nanocrystalline fluoride ion-encapsulated polyhedral oligomeric silsesquioxane (F-POSS) compounds, with substituted electron-withdrawing group (EWG) perfluorinated alkyl chain arms of varying lengths, were investigated.

POSS-Appended Diphenylalanine: Self-Cleaning, Pollution-Protective, and Fire-Retardant Hybrid Molecular Material

Ordered self-assemblies of hybrid molecules have potential as protective umbrellas against environmental pollution and corrosion. This article describes the design and fabrication of a new self-cleaning hybrid molecular material containing polyhedral oligomeric silsesquioxane (POSS) and diphenylalanine as hydrophobic and pollution-protective coating. The colorless organic-inorganic hybrid materials, in which the diphenylalanine motif controls the self-assembly, exhibit unique water resistance property and enhance mechanical strength of paper 1.5-fold. The hybrid building blocks self-assemble in antiparallel sheet manner through noncovalent interactions to form a supramolecular layerlike surface with enhanced roughness. The hybrid material is soluble in organic solvents at room temperature that makes it easy to coat on paper, wood, or metal surfaces. The coating is effective against rusting, corrosion, environmental pollution, and bacterial attack. The coating has been used as fire retardant and enhances fire safety. The sustainable molecular material is promising for the packaging industry and metal industry and artifact preservation.

Solid-state dynamics and single-crystal to single-crystal structural transformations in octakis(3-chloropropyl)octasilsesquioxane and octavinyloctasilsesquioxane

Thermally induced formation of symmetric crystal lattices in functional POSS proceeds via different mechanisms and results in unique reversible phenomena.

Janus-Cube Octasilsesquioxane: Facile Synthesis and Structure Elucidation

A perfect "Janus-cube" octasilsesquioxane, a nanometer-scale Janus particle with two different types of substituents, was synthesized through the cross-coupling of a "half-cube" cyclic sodium siloxanolate with another half-cube cyclic fluorosiloxane. The structure was confirmed by X-ray crystallography to be a Janus cube. The overall synthesis is simple and does not require drastic separation methods compared with previous methods. The synthesis of the Janus cube demonstrates a novel siloxane bond-forming reaction involving the coupling a silanol salt and fluorosilane. The reaction is mild, does not result in acid generation, and could be applied to the construction of other novel siloxane compounds.

Multifunctional imine-POSS as uncommon 3D nanobuilding blocks for supramolecular hybrid materials: synthesis, structural characterization, and properties

Imino-functionalized cage-like octasilsesquioxanes provide unique examples of the 3D supramolecular network and their relationship to the assembly of tunable materials from nanobuilding blocks.

Tetraphenylethene (TPE) modified polyhedral oligomeric silsesquioxanes (POSS): unadulterated monomer emission, aggregation-induced emission and nanostructural self-assembly modulated by the flexible spacer between POSS and TPE

Mono-TPE modified POSS molecules exhibit monomer and AIE emission under different conditions.

Polymeric Flower-Like Microparticles from Self-Assembled Cellulose Stearoyl Esters

Flower-like particles (FLPs) with hierarchical surface architectures have recently attracted considerable attention due to their potentially wide application range. Hitherto, nearly all FLPs were fabricated using inorganic compounds, while versatile organic polymers have not received sufficient attention yet. Herein, we show the construction of novel organic, polymeric FLPs with diameters of 2.5-5 μm using cellulose stearoyl esters (CSEs) by means of the crystallization of side chains. CSEs with degrees of substitution of approximately 3 were transformed into FLPs during the gradual precipitation of polymer chains from the mixture of their solutions in dichloromethane (DCM) and a nonsolvent, which is driven by the evaporation of DCM. Ordered petal-like nanostructures were formed on the particle surface through the crystallization of side chains. Finally, partially crystalline FLPs containing lamellar structures were obtained. Moreover, the formation process was strongly affected by the molecular weight of CSE, concentrations of CSE solutions and the volume ratio between DCM and nonsolvents.

Crystallization and morphology development in polyethylene–octakis(n-octadecyldimethylsiloxy)octasilsesquioxane nanocomposite blends

A detailed study of the crystallization kinetics and morphology development of a novel set of polyethylene–Q₈POSS blends.

Alkylated cage silsesquioxane forming a long-range straight ordered hierarchical lamellar nanostructure

An alkylated cage silsesquioxane (1), targeting for a new class of bottom-up-type fabricating materials, was successfully synthesized, and its self-assembled structure is described and discussed herein. Through this, it was found that the intermolecular interaction of long alkyl chains of 1 could be manipulated by thermal annealing to form a long-range straight ordered hierarchical lamellar structure with a periodicity of around 5 nm. Subsequent transmission electron microscopy (TEM) clearly identified polyhedral oligomeric silsesquioxane (POSS) molecules of 1 arranged in a highly ordered fashion, with a "head-to-head" type bilayered structure. The observation of a sublayer structure measuring approximately 0.4 nm in width was attributed to the highly regular packing of isobutyl groups in POSS molecules identified by TEM analysis. Moreover, the formation of a long-range straight structure with sharp interfacial boundaries, which is difficult to achieve with traditional diblock copolymers, is considered to be of significant importance to developing new practical applications of self-assembled nanostructures.

Alkylated cage silsesquioxanes: a comprehensive study of thermal properties and self-assembled structure

Long-range straight ordered lamellar structures with controllable feature sizes at sub-10 nm scale are created by thoroughly choosing the aliphatic chain length and branch numbers of alkylated cage silsesquioxane.

Synthesis, spectral characterization, self-assembly and biological studies of N-acyl-2-pyrazolines bearing long alkoxy side chains

A series of new pyrazoline derivatives (1b-4c) bearing N-acyl arms and nine to twelve carbon long alkoxy side chains was synthesized and characterized on the basis of spectroscopic data and microanalysis. The nature of self-assembly to understand the interplay of alkoxy chain crystallization and various supramolecular interactions was investigated using single crystal X-ray diffraction studies. Interesting self-assembled supramolecular structures of 1b and 4c were observed in the crystal lattice owing to various CH⋯O, H⋯H, CH⋯π, lonepair⋯π and π⋯π interactions. Further, all the synthesized compounds (1b-4c) were screened for their in vitro antifungal and anti-inflammatory activities. Compounds 2b, 3b, 2c and 3c showed significant to moderate antifungal activity against Microsporum canis whereas most of the other compounds were found inactive against all the five tested fungal strains. Good anti-inflammatory activity was observed for compounds 1b with IC50 value 331 μM compared to 273 μM for Indomethacine, a standard reference drug. The bio-activity data demonstrates the relationship between lipophilicity, solubility and bioavailability.