Silsesquioxane Cages Research Articles

Modifying interlayer space of montmorillonite with octakis(3-(1-methylimidazolium)propyl) octasilsesquioxane chloride

Highly water-soluble material of multi-imidazolium based silsesquioxane cages (material 2) is a promising candidate for modifying clay mineral interlayer space, which is successfully demonstrated by using montmorillonite. The modified montmorillonite can be easily prepared via cation exchange reaction between material 2 and sodium ions of montmorillonite, dispersed in an aqueous solution at room temperature. The modified montmorillonite formed a precipitate within a few seconds. A single layer of material 2 found to be intercalated in the modified montmorillonite with a maximum interlayer space (d-value) of 18 Å (1.8 nm) from 13 Å (1.3 nm) of the unmodified one was confirmed by transmission electron microscopy (TEM) and X-rays diffraction (XRD). Moreover, the percentage uptake and nature of incorporation of material 2 into montmorillonite layers were investigated by thermal gravimetric analyses (TGA), 29Si NMR and FT-IR spectroscopies.

Study of a pulsed post‐discharge plasma deposition process of APTES: synthesis of highly organic pp‐APTES thin films with NH2 functionalized polysilsesquioxane evidences

This article reports the use of pulsed remote Ar‐O2 microwave plasma assisted chemical vapor deposition with an −NH2 containing organosilicon precursor ((3‐Aminopropyl)triethoxysilane: APTES). It is shown that modifying the plasma pulses duration (ton) and the plasma off duration (toff) allows to finely tune the deposited layer composition. In addition, the results of this work demonstrate that an important film growth occurs during toff, which results in an increased −NH2 density. Besides, high resolution MALDI‐ORBITRAP Mass spectrometry analysis clearly points out that APTES oligomers up to eight base units, including silsesquioxanes (cages), and cyclosiloxanes (rings) molecules with intact −NH2 groups are embedded into the as grown pp‐APTES thin film.

Designing a Solution Processable Poly(3,4-ethylenedioxyselenophene) Analogue

A new derivative (EDOS–POSS) of 3,4-ethylenedioxyselenophene integrated with alkyl-substituted polyhedral oligomeric silsesquioxane (POSS) cage was synthesized and characterized. The electroactive monomer was successfully polymerized via both chemical and electrochemical methods. The obtained polymer called PEDOS–POSS was solution-processable and soluble in common organic solvents like tetrahydrofuran, toluene, dichloromethane, and chloroform. PEDOS–POSS polymer exhibited electrochromic behavior: pure blue when neutralized and highly transparent when oxidized. When compared to the parent PEDOS (1.40 eV with λmax = 673 nm), PEDOS–POSS polymer film has a somewhat higher band gap (1.50 eV with λmax = 668 and 724 nm). Also, PEDOS–POSS exhibited high optical contrast ratio (59%) and coloration efficiency (593 cm2/C for 95% switching) with a low switching time (0.7 s) due to the presence of POSS cage in the polymer backbone. In addition, PEDOS–POSS polymer film was highly robust and stable under ambient conditi...

Electrochemical and optical properties of substituted phthalimide based monomers and electrochemical polymerization of 3,4-ethylenedioxythiophene-polyhedral oligomeric silsesquioxane (POSS) analogue

A new series of donor-acceptor-donor type trimeric monomers bearing substituted phthalimide units as acceptor units and thiophene and 3,4-ethylenedioxythiophene (EDOT) as donor units was synthesized and characterized. The strength of acceptor units and intramolecular charge transfer between donor and acceptor units were investigated by using electrochemical and optical methods. The main advantage of phthalimide unit over other acceptor units is the ease of its functionalizability. Thus, utilizing this property, a phthalimide derivative (E2P-POSS) bearing polyhedral oligomeric silsesquioxane (POSS) cage was introduced successfully with EDOT and polymerized electrochemically. The corresponding electroactive polymer, PE2P-POSS, has a band gap of 1.72 eV and is an electrochromic polymer: gray when neutralized and eggplant purple when oxidized.

Covalent grafting of fluoride-encapsulating silsesquioxane F−@Ph8T8 onto glassy carbon

Covalent immobilization of fluoride-encapsulating octaphenyl silsesquioxane F−@Ph8T8 on glassy carbon (GC) was achieved using a new ambifunctional grafting agent, iodomethyltrimethylsilane TMSCH2I. This grafting method did not require any pre-grafting functionalization of the Ph-trimmed substrate; instead, the GC interface was anodically covered with CH2I groups whose ensuing reduction in the presence of F−@Ph8T8 resulted in the covalent grafting of the phenyl silsesquioxane cage onto the GC surface via the CH2 linker(s). The resulting ionic interface can be used to detect exposure to Li+- and H+-containing media. The proposed electrochemical process offers a general method for covalent binding of two (poly)aromatic substrates by a methylene bridge.

Detailed characterization of POSS-poly(ethylene glycol) interaction with model phospholipid membrane at the air/water interface

Polyhedral oligomeric silsesquioxanes (POSS) derivatives have been receiving remarkable attention due to their potential biomedical application and therefore understanding molecular mechanism of their interaction with cell membranes should be studied at molecular level. Here we investigate the binary mixture of an open silsesquioxane cage POSS-poly(ethylene glycol) (POSS-PEG) and 1,2-myristoyl-sn-glycero-3-phosphoethanolamine (DMPE) as a representative of phospholipid located in biological membranes. The surface pressure-area and surface potential-area compression isotherms, as well as Brewster angle microscopy and interfacial shear rheology were used to study monolayers at the air/water interface. The results show that POSS-PEG exhibits an insoluble monolayer with side group chains anchored to the air/water interface. The outcomes of the conducted experiments show (i) the evidence of a stable incorporation of POSS molecule to the DMPE monolayer modifying its equilibrium and dynamic properties and (ii) squeezing the POSS-polymer out of the lipid monolayer at a higher molecular packing density. The results from the conducted experiments together with thermodynamic analysis suggest area condensation and mutual miscibility at the surface pressure relevant to a real biological membrane.

Tridecanuclear CuII11Na2 Cagelike Silsesquioxanes

A series of three unprecedented heterometallic copper(II) sodium silsesquioxanes were isolated (i) via the unusual rearrangement process during synthesis of coordination polymers or (ii) via the self-assembly reaction using 2,2′-bipyridine. The unique type of these products’ molecular topology consists of an unusual fusion of two sandwich-like components (each including five copper and one sodium sites) via a central copper ion. These compounds correspond to the highest nuclearity among Cu(II)-based cage silsesquioxanes reported to date.

Regioisomeric Tandem Triblock Shape Amphiphiles Based on Polyhedral Oligomeric Silsesquioxanes.

We report the design, synthesis and self-assembly of a series of tandem triblock shape amphiphile regioisomers composed of one rod-like fluorinated polyhedral oligomeric silsesquioxane (FPOSS) cage tethered with two spherical tert-butyl-POSS (tBPOSS) cages in para-, meta-, and ortho-configurations. Precision syntheses are achieved through sequential "click" reactions and the compounds are thoroughly characterized by combined techniques of NMR, FT-IR and MALDI-TOF MS spectroscopy. Only the ortho-isomer forms an ordered lamellae structure induced by the crystallization of perfluoroalkyl-chains and the other two remain amorphous due to frustrated packing by unfavorable regio-configuration. The distinct assembly behaviors of these three regioisomers reflect the delicate influence of a minute structural difference on precision macromolecular assembly.

Porous Silsesquioxane-Imine Frameworks as Highly Efficient Adsorbents for Cooperative Iodine Capture.

The efficient capture and storage of radioactive iodine (129I or 131I), which can be formed during nuclear energy generation or nuclear waste storage, is of paramount importance. Herein, we present highly efficient aerogels for reversible iodine capture, namely, porous silsesquioxane-imine frameworks (PSIFs), constructed by condensation of octa(3-aminopropyl)silsesquioxane cage compound and selected multitopic aldehydes. The resulting PSIFs are permanently porous (Brunauer-Emmet-Teller surface areas up to 574 m2/g), thermally stable, and present a combination of micro-, meso-, and macropores in their structures. The presence of a large number of imine functional groups in combination with silsesquioxane cores results in extremely high I2 affinity with uptake capacities up to 485 wt %, which is the highest reported to date. Porous properties can be controlled by the strut length and rigidity of linkers. In addition, PSIF-1a could be recycled at least four times while maintaining 94% I2 uptake capacity. Kinetic studies of I2 desorption show two strong binding sites with apparent activation energies of 77.0 and 89.0 kJ/mol. These energies are considerably higher than the enthalpy of sublimation of bulk I2.

Synthesis and properties of hyperbranched polymers by polymerization of an AB3-type incompletely condensed cage silsesquioxane (IC-POSS) monomer

An incompletely condensed cage silsesquioxane (IC-POSS)-based AB3-type monomer, tris(dimethylsilyl)-p-vinylhexaisobutyl-IC-POSS (3), was prepared by the corner-cleaved reaction of vinylheptaisobutyl-POSS (1) and subsequent capping reaction with chlorodimethylsilane. The structure of 3 was confirmed by FT-IR; 1H-, 13C-, and 29Si-NMR; and HR-FAB-MS analyses. These analyses also suggested 12.5 mol% contamination of tris(dimethylsilyl)-heptaisobutyl-IC-POSS (4). The hydrosilylation polymerization of 3 as an AB3-type IC-POSS monomer in the presence of Karstedt’s catalyst in toluene at 80 °C overnight provided a soluble polymer with a number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) of the polymer that are 3.9 × 103 and 1.39, respectively. The resulting hyperbranched polymer (HB) reacted with two molar equivalents of isoprenol or allylheptaisobutyl-POSS against the Si–H groups in the presence of Karstedt’s catalyst in toluene at 80 °C for 7 h. The HB polymers before and after post functionalization with isoprenol or allylheptaisobutyl-POSS showed 1% weight loss at 298, 285, and 358 °C, respectively, under N2. Introducing POSS units at the terminus significantly increased the thermal stability. The XRD pattern of the HB polymers showed a denser structure formed in the allylheptaisobutyl-POSS-terminated HB polymer. The refractive index of the HB polymer before post functionalization was 1.4376. Post functionalization with isoprenol and allylheptaisobutyl-POSS increased the refractive index to 1.4464 and 1.4573, respectively. An incompletely condensed cage silsesquioxane (IC-POSS)-based AB3-type monomer, tris(dimethylsilyl)-p-vinylhexaisobutyl-IC-POSS (3), was prepared by the corner-cleaved reaction of vinylheptaisobutyl-POSS (1) and subsequent capping reaction with chlorodimethylsilane. The hydrosilylation polymerization of 3 in the presence of Karstedt’s catalyst in toluene provided a soluble polymer. The refractive index of the unmodified polymer film was 1.4376. Post functionalization with isoprenol increased the dispersibility in polar organic solvents and significantly increased the glass-transition temperature. Post functionalization with allylheptaisobutyl-POSS significantly increased the thermal stability. Their refractive index varied from 1.4464 to 1.4573 upon post functionalization.

Hyperbranched Polysiloxanes Based on Polyhedral Oligomeric Silsesquioxane Cages with Ultra-High Molecular Weight and Structural Tuneability

Hyperbranched siloxane-based polymers with ultra-high molecular weight were synthesized by the Piers–Rubinsztajn reaction between octakis(dimethylsiloxy) octasilsesquioxane with different dialkoxysilanes, using tris(pentafluorophenyl) borane as the catalyst. The origin of the high molecular weight is explained by the high reactivity of the catalyst and strain energy of isolated small molecule in which all eight silane groups close into rings on the sides of a single cubic cage. The structural tuneability was further demonstrated by use of methyl(3-chloropropyl)diethoxysilane, which generates a polymer with similar ultra-high molecular weight. Introduction of phosphonate groups through the chloropropyl sites later leads to functionalized polymers which can encapsulate various transition metal nanoparticles.

Heptanuclear Cage CuII‐Silsesquioxanes: Synthesis, Structure and Catalytic Activity

Two prismatic phenyl‐ (PhSiO1.5)14(CuO)7 (1, 29 % yield) and methyl‐ (MeSiO1.5)14(CuO)7 (2, 19 % yield) heptacoppersilsesquioxanes were obtained by the interaction of Cu,Na‐based cage silsesquioxanes [(RSiO1.5)12(CuO)4(NaO0.5)4] (R = Ph, Me) with 4,4′‐bipyridine and pyrazine, respectively, acting as “silent witness” ligands. Unusual molecular topologies of both compounds 1 and 2, which are the first representatives of cage silsesquioxanes with seven metal ions in their cores, were established by X‐ray diffraction studies. Complex 1 was found to be an active precatalyst in the oxidation of alkanes and 1‐phenylethanol to alkyl hydroperoxides and acetophenone, respectively. Alkanes were oxidized by hydrogen peroxide, and the alcohol was oxidized by tert‐butyl hydroperoxide.

High-Nuclearity (Cu8-Based) Cage Silsesquioxanes: Synthesis and Structural Study

We herein report a study of Cu(II)-silsesquioxanes’ self-assembly in the presence of two possible template agents (acetonitrile and acetone). This results in the isolation of unusual high-nuclearity cluster CuII8 cage silsesquioxanes [(Ph8Si8O16)2Cu8(DMF)8][Ph8Si8O12]·2MeCN 1 and [(Me8Si8O16)2Cu8(Me2CO)4]2[MeCOO–]2[Na+]2·2(H2O)·3(Me2CO) 2. In the case of 1, acetonitrile indeed serves as a template being incorporated into the inner void of the prism-like cage of the crystalline product. To the contrary, in the case of complex 2, acetone molecules just play the role of external solvates. An inner void of the prism-like cage in 2 is occupied by sodium acetate groups. The latter, most likely, are produced via the mild oxidation of ethanol during the synthesis of 2. Finally, the sodium centers of these acetate groups caused an unprecedented “cage connectivity” (dimerization of two octacopper cage silsesquioxanes in 2).

Hydrophobic ultrathin films formed by fluorofunctional cage silsesquioxanes

The usefulness of fluorofunctional cage silsesquioxanes (POSS) as coating materials effectively changing the surface properties of model substrates was analyzed. Five fully condensed silsesquioxanes (containing two types of organic groups attached to the Si-O cage: octafluoropentyloxypropyl (OFP) and trimethoxysilylethyl (TMS) at different ratios, one monofunctional derivative with OFP groups only and one open cage POSS derivative with three OFP and seven isobutyl groups as organic substituents were investigated. All POSS derivatives were applied to enhance hydrophobicity of quartz or glass plates by deposition of thin LB film transferred from the water subphase. Then, by comparison of water contact angles (WCA) on modified surfaces the effect of silsesquioxane structure (i.e. the TMS and fluoroalkyl group contents as well as the structure of silicon-oxygen cage) on hydrophobic properties was determined. Moreover, the texture of LB films formed by POSS considered was analyzed using the AFM technique. It has been established that the hydrophobizing properties of silsesquioxanes are considerably influenced not only by the number of OFP groups, but also by the silsesquioxane structure. The most effective appeared to be the open cage OFP-POSS derivative which produced coatings with water contact angles (WCA) equal to about 100 deg. Additionally the POSS derivatives studied were also used for dip-coating and spin-coating surface modification. The study has shown that fluorofunctional POSS derivatives can be effective hydrophobizing agents. Additionally applying the LB technique for surface modification allows obtaining substrate of enhanced hydrophobicity by using vanishingly small amount of the modifying substance in comparison to the dip-coating and spin-coating method, which is especially important from the economic viewpoint.

Self-association behavior of amphiphilic molecules based on incompletely condensed cage silsesquioxanes and poly(ethylene glycol)s

Polyhedral oligomeric silsesquioxane (POSS) is an important building block for constructing organic-inorganic hybrid molecules or polymers. In this work, we report amphiphilic, incompletely condensed POSSs (IC-POSSs) possessing various substituents on the seven silicon atoms and two kinds of poly(ethylene glycol)s (PEGs) with different chain lengths. The IC-POSS cores possessed comparable thermal stability to that of the completely condensed POSS (CC-POSS) analogs, despite their open cage structure. The amphiphilic IC-POSSs formed micelles of different sizes and had polydispersity indices (PDIs) that were dependent on the substituents and the PEG chain length. Additionally, the lower critical solution temperatures (LCSTs) were observed for amphiphilic IC-POSSs possessing shorter PEG chains, while aqueous solutions of those with longer PEG chains showed high transmittance even at 80 °C. Amphiphilic incompletely condensed polyhedral oligomeric silsesquioxanes possessing various substituents and poly(ethylene glycol)s of different chain lengths have been developed. It has been elucidated that their self-association behaviors in water are dependent on the substituents and chain lengths of poly(ethylene glycol)s. Precise molecular design, excellent thermal stability, and good dispersibility have been realized at once.

Anion identification using silsesquioxane cages.

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.

Family of penta- and hexanuclear metallasilsesquioxanes: Synthesis, structure and catalytic properties in oxidations

The deliberate synthesis of two types of prismatic cage-like metallasilsesquioxanes (hereinafter, referred to as CLMSs), viz., penta- and hexanuclear ones, is reported. It is shown that the size of the prismatic cage can be readily and reliably controlled by synthesis parameters. More specifically, the nuclearity shift from six, which is most common in CLMS chemistry (complexes 1–6, 8), to five, which is observed significantly more rarely, is achieved by applying pyridine as a key solvent/crystallization medium (complexes 7, 9–12). Structures of 1–12 were established by single-crystal X-ray diffraction. In sum, their composition could be described as [PhSiO1.5]12[CuO]6 (for hexanuclear products) or [RSiO1.5]10[MO]5 (R = Ph, Vin, M = Cu, Ni, Co for pentanuclear products). Compounds 7, 9–10 represent the rare examples of cage silsesquioxanes comprising pentagonal metalla-oxa rings of Cu(II) ions. The complex 10 is the very first observation of a co-crystal composed of different CLMS (i.e., two Co(II)5 and one Cu(II)5 prismatic cages). The compound 12 (Co5 cage with vinyl substituents at the silicon atoms) is the very first example of a pentanuclear CLMS-based coordination polymer. Complex 7 efficiently catalyzes oxidation of secondary alcohols to the corresponding ketones and alkanes to the corresponding alkyl hydroperoxides.

Improvement of optical properties and redox stability of poly(3,4-ethylenedioxythiophene)

In order to improve the optical properties and redox stability of poly(3,4-ethylenedioxythiophene) (PEDOT) without changing its electrochemical and electrochromic behaviour, it was supported with alkyl-substituted polyhedral oligomeric silsesquioxane (POSS) cage. The corresponding copolymers were obtained electrochemically via potentiostatic or potentiodynamic methods and compared to the parent homopolymers. Electrochemical polymerization of EDOT and POSS containing EDOT called EDOT-POSS in various monomer feed ratios was performed in an electrolyte solution of 0.1 M TBAPF6 dissolved in a mixture of dichloromethane and acetonitrile (1/3: v/v). Just as PEDOT, the copolymers represented the similar band gap (1.61 eV), redox and electrochromic behaviors. On the other hand, when compared to the parent PEDOT, the presence of POSS cages in the copolymer backbone improved the redox stability and optical properties of PEDOT such as higher percent transmittance change (65% at 621 nm), higher transparency at oxidized state, lower switching time (∼1.0 s) and higher coloration efficiency (463 cm2/C for 95% switching) as well as higher electrochemical stability (86% of its electroactivity retains after 1750 cycles under ambient conditions).

Preparation and Molecular Structure of a Cyclopentyl-Substituted Cage Hexasilsesquioxane T6 (T = cyclopentyl-SiO1.5) Starting from the Corresponding Silanetriol

Cyclopentyl substituted silanetriol can be prepared and isolated. Its condensation yields the corresponding disiloxanetetrol as a primary condensation product. Further condensation leads to the hexameric polyhedral silsesquioxane cage T6. The latter has been mentioned in the literature before however, lacking structural data. All compounds have been characterized with multinuclear NMR spectroscopy and, in addition, the molecular structures have been determined in the case of the disiloxanetetrol and the hexasilsesquioxane via single crystal X-ray diffraction.

A platform to synthesize a soluble poly(3,4‐ethylenedioxythiophene) analogue

ABSTRACTAlkyl‐substituted polyhedral oligomeric silsesquioxane (POSS) cage is combined with 3,4‐ethylenedioxythiophene under the same roof. The corresponding monomer called EDOT‐POSS is used to get soluble poly(3,4‐ethylenedioxythiophene) (PEDOT‐POSS) analogue. Both chemically and electrochemically obtained polymers are soluble in common organic solvents like dichloromethane, chloroform, tetrahydrofuran, and so forth. The PEDOT‐POSS has somewhat higher band gap (1.71 eV at 618 nm) than its parent PEDOT (1.60 eV at 627 nm) and as expected the PEDOT‐POSS exhibits higher optical contrast (74% at 618 nm) and coloration efficiency (582 cm2/C for 100% switching), lower switching time (0.9 s), higher electrochemical stability (93% of its electroactivity retains after 5000 cycles under ambient conditions) when compared to the PEDOT. A number of advantages of the PEDOT‐POSS over the PEDOT can make it a promising material in the areas of electro‐optical applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3935–3941