Silsesquioxane Derivatives Research Articles

Organic Thin Film Transistors Using a Polyhedral Oligomeric Silsesquioxane-Based Photo-Patternable Insulating Material

We synthesized a new photo-patternable organic/inorganic hybrid material, polyhedral oligomeric silsesquioxane (POSS) derivative containing cyclohexene-1,2-epoxide functional groups (POSS-EPOXY), and fabricated an organic thin film transistor (OTFT) using pentacene as an active p-type organic semiconductor and POSS-EPOXY as a gate dielectric layer to demonstrate its applicability for organic electronics. The pentacene transistor with the POSS-EPOXY layer shows comparable transistor characteristics as that with the prototypical polymeric gate insulator of poly(vinylphenol) (PVP). They exhibit field-effect mobility of micro(FET) approximately 0.075 cm2/Vs, threshold voltage of V(T) = -22.2 V, the on/off current ratio of 7 x 10(5), and the subthreshold slope of 3.9 V/dec.

Preparation and characterization of styrene/styryl–polyhedral oligomeric silsesquioxane hybrid copolymers

AbstractBACKGROUND: Organic–inorganic nanocomposites were prepared by copolymerization of various monomers and polyhedral oligomeric silsesquioxane (POSS) derivatives. Preliminary results showed that styrene/styryl–POSS copolymers could be obtained using CpTiCl3 catalyst. In the work reported here, the copolymerization of styrene and styryl‐substituted POSS was studied in detail for a more effective catalyst, Cp*TiCl3.RESULTS: The glass transition temperature (Tg) of the copolymers prepared increased with increasing POSS content. The degradation temperature (Td) of the copolymers was 60 °C higher than that of syndiotactic polystyrene under nitrogen. Although the thermal properties were improved by incorporation of POSS, the catalytic activity decreased with POSS content. The racemic triad and syndiotactic index of the copolymers decreased with increasing POSS content. Gel permeation chromatograms of the copolymers exhibited multimodal distribution due to the presence of multi‐active centres, which were formed by interaction of Ti with the POSS siloxane linkage.CONCLUSION: With the incorporation of POSS, the thermal properties of polystyrene were improved. The styrene/styryl–POSS copolymers are formed through the various active sites arising from the interactions of Ti with POSS. Copyright © 2008 Society of Chemical Industry

Organic Thin Film Transistor Using a Photo-Curable Organic/Inorganic Hybrid Material as a Gate Dielectric

A polyhedral oligomeric silsesquioxane derivative (POSS-OXT) containing photo-curable 4-membered cyclic oxetane functional groups was used as a gate dielectric of organic field effect transistor. The POSS-OXT was cross-linked and completely solidified by UV irradiation in the presence of a selected photo acid generator, and pinhole free uniform thin film was obtained. We fabricated a metal/insulator/metal device of Au/POSS-OXT (300 nm)/Au with area of 0.7 mm2 and the measured leakage current and capacitance of the device to evaluate the insulating properties of the POSS-OXT thin film. The maximum current was about 0.25 nA when 40 V was applied to the device. The observed values of the capacitance per unit area and dissipation factor were 11.4 nF/cm2 and 0.025, respectively. We fabricated an organic thin film transistor with pentacene as the active semiconductor and the photo-cross-linked POSS-OXT as an insulator. A field effect carrier mobility of 0.03 cm2/VN s was obtained with the device.

A simple approach toward low‐dielectric polyimide nanocomposites: Blending the polyimide precursor with a fluorinated polyhedral oligomeric silsesquioxane

AbstractThis article describes a new and simple method for preparing polyimide nanocomposites that have very low dielectric constants and good thermal properties: simply through blending the polyimide precursor with a fluorinated polyhedral oligomeric silsesquioxane derivative, octakis(dimethylsiloxyhexafluoropropyl) silsesquioxane (OF). The low polarizability of OF is compatible with polyimide matrices, such that it can improve the dispersion and free volume of the resulting composites. Together, the higher free volume and lower polarizability of OF are responsible for the lower dielectric constants of the PI‐OF nanocomposites. This simple method for enhancing the properties of polyimides might have potential applicability in the electronics industry. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6296–6304, 2008

Synthesis and characterization of amorphous octakis-functionalized polyhedral oligomeric silsesquioxanes for polymer nanocomposites

We have synthesized the polyhedral oligomeric silsesquioxane (POSS) derivatives OS-POSS and OA-POSS through the hydrosilylation of styrene and 4-acetoxystyrene, respectively, with octakis(dimethylsiloxy)silsesquioxane (Q8M8H). We then prepared OP-POSS through acetoxyl hydrazinolysis of OA-POSS with hydrazine monohydrate. The chemical structures of these POSS derivatives were characterized using FTIR and 1H NMR spectroscopy and MALDI-TOF mass spectrometry. Unlike Q8M8H, which is crystalline, these three hydrosilylated POSS derivatives are liquids at 25°C. Through DSC and XRD analyses, we found that they exhibit polymer-like glass transitions and amorphous halos. These octakis-functionalized POSS derivatives can be regarded as amorphous glasses possessing low glass transition temperatures, the values of which depend on the intermolecular interactions of their outer organic groups. To investigate the dispersion of these POSS derivatives in polymer nanocomposites, we blended OS-POSS, OA-POSS, and OP-POSS with polystyrene, poly(4-acetoxystyrene), and poly(4-vinylpyridine), respectively, and investigated the effects of the resulting intermolecular aromatic hydrophobic, dipole–dipole, and hydrogen-bonding interactions, respectively. Dipole–dipole interactions provided the best dispersion of OA-POSS in poly(4-acetoxystyrene), in which the POSS–polymer intermolecular interactions were of similar strength to the POSS–POSS interactions.

Synthesis and applications of functionalized silsesquioxane polymers attached to organic and inorganic matrices

Abstract Organofunctionalized silsesquioxane polymers obtained in a water-soluble form can be used to coat various substrates such as SiO2, SiO2/Al2O3, Al2O3, cellulose/Al2O3, and graphite or, when obtained in a water-insoluble form, can be used directly. These organofunctionalized silsesquioxanes can also be attached to poly(dimethylsiloxane) (PDMS) polymers. The functional groups constituted by neutral amine groups or cationic groups (pyridinium, 3- and 4-picolinium, or 1,4-diazabicyclo[2.2.2]octane (DABCO), mono- or -dicationic) have relatively high affinity for metal ion in ethanol solutions, as shown by their stability constants. Materials containing attached cationic functional groups have also been efficiently used to immobilize various electroactive species and to construct electrochemical sensors for analytical applications. This work discusses the preparation of silsesquioxane derivatives, their characterization as prepared and when dispersed on several substrates, and comments on some applications of these materials, with an emphasis on the metal adsorption process and manufacture of electrochemical sensors.

Controlling POSS dispersion in epoxy in nanocomposite by introducing multi-epoxy POSS groups

In recent years, polyhedral oligomeric silsesquioxanes derivatives, providing nano-reinforcement, have been extensively employed to reinforce polymers by forming a nanocomposite. Incorporating POSS particles into linear thermoplastics or thermosetting networks markedly improves the thermal [1], dimensional stability [1] and oxidative [2] properties of several polymer resins, extending their applications as high-performance engineering plastics. Numerous thermoplastics and some thermosetting systems have thus been enhanced. These include methacrylates, [3, 4] styrenes, [5] norbornenes, [6] siloxanes [7] and epoxies [1, 8–11]. Multi-functional POSS derivatives such as epoxy resin, [1, 8– 11] polyurethane, [12] polyacrylate, [13] polyimide, [14, 15] and polybenzoxazine [16, 17] have been utilized as curing junctions, further increasing the crosslinking density of the polymer. Introducing ‘‘multi-functional’’ POSS derivatives results in interesting thermal and mechanical characteristics. Two of the factors that significantly affect the thermal and mechanical characteristics of the nanocomposite systems are the crosslinking density and the dispersion state of nanofillers in the nanocomposite matrix. According to the character of substituents, types of the aggregated POSS within matrix could behave either as nanofiller reinforcing the matrix or as the plasticizer. In particular, the dispersion of nanofillers in the nanocomposite matrix is an important issue that has been studied by many scientists, because the crosslinking density [18] of the nanocomposite is related to the dispersion of the nanofillers therein. In nanocomposites with multi-functional POSS derivatives, POSS derivatives can react with the monomer units of the polymer, increasing their crosslinking density [12, 16, 19]. In some cases [15, 20–23], the POSS derivatives react with the monomers of the polymer. The POSS that is aggregated inside the nanocomposite matrix behaves as the plasticizer, as revealed by the less favorable thermal properties. In this work, dynamic curing kinetics were utilized to evaluate the reactivity between the soft epoxy/DDM system and cured derivatives of multi-functional POSS (OG) (The octaepoxy-POSS monomer (OG) has eight epoxide functional groups). The reactivity between soft epoxy and OG cured with a DDM, enables further the dispersion state of POSS in the nanocomposite matrix to be verified. Based on the assumption that OG reacts with DDM more rapidly than does soft epoxy that has been cured with DDM, since DDM is inserted into OG such that the aggregation declines as OG reacts with DDM, the reactivity of nanocomposite by multifunctional derivatives octaepoxy-POSS will be investigated by introducing multi-functional POSS derivates to understand the POSS dispersion state of nanocomposite.

Immobilization of titanium chiral alkoxides on SBA-15 and modelling the active sites of heterogeneous catalyst using titanium silsesquioxane complexes

A molecular precursor approach involving simple grafting procedures was used to produce site isolated titanium-supported epoxidation catalysts. The complexes [{Ti(O iPr) 2(OMent)} 2] ( 1) and [Ti(OMent) 4] ( 2) (MentO = 1 R,2 S,5 R-(−)-menthoxo) react with the remaining hydroxyl groups of SBA-15 after silanization with Me 3SiCl, via loss of iPrOH and/or menthol and introduction of titanium species onto the silica surface. Grafting 1 and 2 onto SBA-15 yields mostly isolated Ti(IV) sites, as evidenced by DRUV–vis. In addition, the silsesquioxane derivatives [Ti(O iPr) 2(OMent){(c-C 5H 9) 7Si 8O 13}] ( 3) and [Ti(OMent) 3{(c-C 5H 9) 7Si 8O 13}] ( 4) have been synthesized in order to compare the different homogeneous and heterogenous systems mentioned above in the asymmetric epoxidation of cinnamyl alcohol to evaluate their catalytic activity and enantioselectivity.

The influence of shape and size of silyl units on the properties of bent-core liquid crystals—from dimers via oligomers and dendrimers to polymers

A series of oligomeric and dendritic liquid crystalline materials combining mesogenic bent-core units and silicon-containing linking units (siloxanes and carbosilanes) was synthesized and investigated. The influence of the size and shape of the silyl units upon the mesophase type and the switching behaviour was investigated. Linear oligosiloxane based dimers and dendritic carbosilanes show ferroelectric and non-classical antiferroelectric switching monolayer smectic phases with dark conglomerate textures coexisting with achiral domains, whereas cyclic oligosiloxane and silsesquioxane derivatives have antiferroelectric switching and birefringent smectic phases with double layer structure. It is concluded that ferroelectricity and layer distortion require a certain size of the silyl groups and a monolayer structure where each layer is decoupled by sublayers formed by the silylated units.

Properties of polystyrene and polymethyl methacrylate copolymers of polyhedral oligomeric silsesquioxanes: A molecular dynamics study

AbstractMolecular dynamics simulations were carried out on copolymers of both styrene and methyl methacrylate with polyhedral oligomeric silsesquioxane (POSS) derivatives to identify the origin of the property changes imparted upon the chemical incorporation of POSS. Simulations were carried out on these hybrid copolymers and the parent homopolymers to elucidate the effect of the T8, T10, and T12 POSS cages. These POSS comonomers were derivatized with a single polymerizable function and 7, 9, and 11 nonpolymerizable hydrocarbon moieties, respectively. Glass transition temperatures (Tg) were computed from specific volume versus temperature plots. The packing of POSS units around the polymer backbone was analyzed via their radial distribution functions. The effect of POSS on polymer motion was analyzed through the mean square displacement function. The improvements in the elastic moduli upon incorporation of POSS were computed by employing the static deformation method. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 234–248, 2006

Thermal and mechanical properties of polyhedral oligomeric silsesquioxane (POSS)/polycarbonate composites

A series of composite materials were produced incorporating polyhedral oligomeric silsesquioxane (POSS) derivatives into polycarbonate (PC), by melt blending. Significant differences in compatibility were observed depending on the nano-scale filler's specific structure: trisilanol POSS molecules generally provided better compatibility with PC than fully-saturated cage structures, and phenyl-substituted POSS grades were shown to be more compatible with PC than fillers with other functional groups. Trisilanolphenyl-POSS/PC composites possess the best overall performance among the POSS materials tested. The high compatibility between the trisilanolphenyl-POSS and polycarbonate matrix results in generation of transparent samples up to 5 wt% POSS content. Slightly enhanced mechanical properties including tensile and dynamic mechanical modulus are observed with the increase of trisilanolphenyl-POSS loading at the cost of decreasing ductility of the nanocomposites. Importantly, upon orientation of the PC/POSS nanocomposite, crystallization of POSS within the oriented material results—this observation is consistent with a growing number of observations which suggest that ‘bottom-up’ formation of structures incorporating multiple POSS cages result from orientation of these nanocomposites, and that the hybrid organic–inorganic inclusions may be at the heart of observed nano-scale reinforcement.

Silyl‐functionalized Silsesquioxanes: New Building Blocks for Larger Si‐O‐Assemblies, including the First Si‐Si‐Bonded Silsesquioxanes

AbstractNovel silyl‐functionalized silsesquioxane building blocks have been prepared by treatment of Cy7Si7O9(OH)3 (1, Cy = c‐C6H11) with hexachlorodisilane or hexachlorodisiloxane, respectively, in the presence of triethylamine. Reactions in a 1:1 molar ratio afforded the trichlorosilyl‐functionalized silsesquioxane derivatives Cy7Si8O12SiCl3 (2) and Cy7Si8O12OSiCl3 (3). Related bis(silsesquioxanes), (Cy7Si8O12)2 (4) and (Cy7Si8O12)2O (5) are accessible in a similar manner by employing a 2:1 molar ratio of the reactands. Compound 1 also served as a starting material in the preparation of the partially closed silsesquioxane cages Cy7Si7O11(OH)SiMe2 (6) and Cy7Si7O11(OH)Si(OEt)2 (7), while the related condensation product Cy7Si7O10(OSiMe3) (9) was made by AlCl3‐catalyzed elimination of water from Cy7Si7O9(OH)2OSiMe3 (8). The molecular structure of 9 was determined by X‐ray diffraction.

Fully Metalated Silsesquioxanes: Building Blocks for the Construction of Catalyst Models

Versatile building blocks for the construction of molecular models for heterogeneous catalysts are readily available in high yields in the form of fully metalated silsesquioxane derivatives, such as dimeric 1, by using alkali-metal silylamides as deprotonating agents.

Hybrid inorganic/organic crosslinked resins containing polyhedral oligomeric silsesquioxanes

AbstractThe incorporation of both monofunctional and multifunctional polyhedral oligomeric silsesquioxane (POSS) derivatives into crosslinked resins has been conducted as a route to synthesize hybrid organic/inorganic nanocomposites. The central cores of POSS molecules contain an inorganic cage with (SiO1.5)n stoichiometry where n=8,10 and 12. Each Si atom is capped with one H or R function giving an organic outer shell surrounding the nanometer‐sized inorganic inner cage. By including polymerizable functions on the R groups, a hybrid organic/inorganic macromer is obtained which can be copolymerized with organic monomers to create thermoplastic or thermoset systems. We have focused on incorporating POSS derivatives into crosslinking resins of the following types: (1) dicyclopentadiene (2) epoxies (3) vinyl esters (4) styrene‐DVB (5) MMA/1,4‐butane dimethacrylate (6) phenolics and (7) cyanate esters. One goal has been to determine if molecular dispersion of the POSS macromers has been achieved or if various degrees of aggregation occur during crosslinked resin formation. As network formation proceeds, a kinetic race between POSS molecular incorporation into the network versus phase separation into POSS‐rich regions (which then polymerize) occurs. Ultimately, we hope to determine the effects of such microstructural features on properties. Combustion of these hybrids creates a SiO2‐like surface layer that retards flame spread. Dynamic mechanical properties have been studied.

Silsesquioxane Chemistry, 4.: Silsesquioxane Complexes of Titanium(III) and Titanium(IV)

Reaction of the incompletely condensed silsesquioxane derivative Cy 7Si 7O 9(OH) 3 ( 1) with Ti(OEt) 4 affords the dimeric titanasilsesquioxane [(Cy 7Si 7O 12)Ti(μ-OEt)(EtOH)] 2 ( 13) in 81% yield. The known titanasilsesquioxane [Cy 7Si 7O 11(OSiMe 3)] 2Ti ( 18) has been prepared through a modified procedure starting from titanium tetraalkoxides. Novel oxotitanium silsesquioxane derivatives are obtained from reactions of titanocene dihalides with Cy 7Si 7O 9(OH) 2(OSiMe 3) ( 14). Cp 2TiCl 2 yields dinuclear (μ-O)[{Cy 7Si 7O 11(OSiMe 3)}TiCp] 2 ( 19), while with Cp * 2TiCl 2 the trinuclear titanacycle Cp * 2Ti 3O 3[Cy 7Si 7O 11(OSiMe 3)] 2 ( 20) is obtained. In addition, a new synthetic route to model compounds for titanium catalysts immobilized on silica has been developed. Disilylated Cy 7Si 7O 9(OH)(OSiMe 3) 2 ( 15) cleanly reacts with the ‘tucked-in’ fulvene complex Cp*Ti(C 5Me 4CH 2) to give the titanium(III) silsesquioxane Cp* 2Ti[Cy 7Si 7O 10(OSiMe 3) 2] ( 21). In a similar manner treatment of Cp*Ti(C 5Me 4CH 2) with Cy 7Si 7O 9(OH) 2(OSiMe 3) ( 14) affords the mono(pentamethylcyclopentadienyl) complex Cp*Ti[Cy 7Si 7O 11(OSiMe 3)][Cy 7Si 7O 10-(OH)(OSiMe 3)] ( 22) which is an advanced model compound for a catalytically active titanium center on a silica surface. The molecular structures of these titanium silsesquioxane derivatives have been determined by X-ray diffraction analyses.

Chitosan–Oligo(silsesquioxane) Blend Membranes: Preparation, Morphology, and Diffusion Permeability

Preparation of the blend chitosan (CHI) membranes containing polyhedral oligomeric silsesquioxane (POSS) derivatives was investigated. POSS derivatives such as (3-aminopropyl)isobutyl-POSS (amino-POSS), [2-(3,4-epoxycyclohexyl)ethyl]isobutyl-POSS (epoxy-POSS), and octa(tetramethylammonium)-POSS were used. The blend CHI–amino-POSS membranes were predicted to be the most porous due to having the weakest interactions between the components in the blends. The CHI–epoxy-POSS blend membranes were assumed to be more dense owing to chemical binding of the chitosan amino groups with the epoxy groups of POSS. Studies of membrane morphology and diffusion permeability support these predictions.

Silsesquioxane Chemistry, 5. Retention of the Cu 4O 4 core upon formation of the first copper(I) silsesquioxane from tetrameric copper(I)- t-butoxide

The first copper(I) silsesquioxane derivative, Cu 4O 4[Cy 7Si 7O 9(OSiMe 3)] 2 ( 4) was prepared by reacting tetrameric copper(I)- t-butoxide, (CuO tBu) 4 ( 3), with the monosilylated silsesquioxane precursor Cy 7Si 7O 9(OH) 2(OSiMe 3) ( 2) in a 1:2 molar ratio. An X-ray diffraction study revealed the presence of a centrosymmetric dimer. A slightly puckered Cu 4O 4 ring forms the central part of a complex structure comprising nine eight-membered inorganic ring systems.

Silsesquioxane chemistry, 6 : The first beryllium silsesquioxane: synthesis and structure of [Cy 7Si 7O 12BeLi] 2·2THF

The compound [Cy 7Si 7O 12BeLi] 2·2THF ( 3) was prepared in high yield by reacting in situ prepared Cy 7Si 7O 9(OLi) 3 ( 2) with anhydrous BeCl 2 in THF at 20°C. The molecular structure of 3 has been determined by X-ray diffraction and is the first structurally characterized silsesquioxane derivative of beryllium. In the solid state, self-assembly leads to the formation of a dimeric molecule.

Advances in Homogeneous and Heterogeneous Catalysis with Metal-Containing Silsesquioxanes

Metal-containing silsesquioxane derivatives provide new catalysts with both homogeneous and heterogeneous applicability. The steric and electronic properties of silsesquioxane silanolate ligands render metal centers more Lewis acidic than conventional alkoxide or siloxide ligands do. This concept has been exploited in newly developed catalysts for alkene metathesis, polymerization, epoxidation, and Diels-Alder reactions of enones. Other applications are envisioned in the near future.

Molecular insight into the non-innocence of a silica-support: the structure of a platinum–silsesquioxane derivative

The cyclooctadiene ligand within the square planar Pt(II) complex [PtCl2(C8H12)] undergoes nucleophilic attack from a siloxo group of the thallated polyhedral silsesquioxane [(c-C5H9)7Si7O9 (OSiMe3)(OTl)2], to yield [(c-C5H9)14Si14O 18(OSiMe3)2O4(η4 -C8H12)PtTl2]; given the analogy between the silsesquioxane moiety and a silica surface, the presence of an SiO–C bond between the siloxo-cage and the Pt-bound olefinic ring is significant in the context of surface non-innocence in heterogeneous catalysis.