Octafunctionalized silsesquioxanes [(RsiO1.5)8, cubes] offer potential as rigid, hard nanoplatforms to which a variety of organofunctional groups can be appended. Crosslinking these groups leads to novel organic/inorganic nanocomposites that consist primarily of interfacial interactions. These materials can be 100% interphase. We present efforts to develop nanocomposite materials that consist of both continuous and discontinuous organic/inorganic phases. We then discuss methods of probing the properties of these materials.

In-situ filling through hydrolysis and condensation of silicon alkoxides dissolved into polymers has been utilized to generate nanocomposites in which the filler phase can be intimately associated with the polymer on relatively small length scales. One problem of the method has been achieving useful fill volumes without bulk phase separation of the growing inorganic component from the polymer. In this paper, we describe the preparation of a new class of nanocomposite materials in which the inorganic filler phase is pre-assembled before copolymerization with an organic monomer. Maleimide monomers, prepared from alkoxysilylpropyl amines and maleic anhydride, were protected against side reactions by forming the oxonorbornene Diels-Alder adduct with furan. The monomers were then reacted under solgel conditions to form oligomers or polymers making up the filler phase. The material was activated by thermal deprotection of the maleimide and reacted with organic monomers or polymers to form the filled nanocomposite.

Organically modified silicates have been prepared, using methyltriethoxysilane and tetraethoxysilane in various molar ratios. The final network is thus composed of trifunctionnal T units and tetrafunctionnal Q units. Three types of oxo bridges can be formed through the competitive self-condensation or co-condensation reactions : (T)-O-(T), (Q)-O-(Q) and (T)-O-(Q). 17O-enriched water was used as reactant in order to selectively enrich the various oxo bridges, and to perform 17O solid state MAS-NMR. The combination of MAS experiments recorded at two different magnetic fields, and of the recently discovered MQ-MAS experiments allowed us to identify clearly the three types of oxo bridges. Quantitative analysis was extracted from the MAS-NMR spectra, and compared with calculations based on randomly distributed Si units.

The lack of storage stability of organic-inorganic solvent-free sols is a well-known problem. We investigated the influence of different solvents in the acid catalyzed hydrolysis of various sols on their storage stability. Our experiments were based on two different silanes, 3-methacryloxypropyltrimethoxysilane (MPTS) and 1,1,1-tris(allyloxymethyl)-l-[[[3-(triethoxysilyl)propyl]aminocarbonyl]oxymethyl]methane (silane 31), synthesized by reaction of pentaerythritol triallyl ether and 3-isocyanatopropyltriethoxysilane. The employed solvents were alcohol, tetrahydofuran and tert-butyl methyl ether in a range of 95 wt% to 30 wt% in solution. In order to get comparable chemical conditions the degree of condensation of the various sols were adjusted between 75% and 85%. Furthermore, the sols were modified by silylation with trimethylchlorosilane. A comparison of silylated and not silylated silane 31 clearly showed that a decrease in residual silanol groups increase the storage stability. The results of the investigations demonstrated that both the kind and the amount of solvent used in hydrolysis affects the initial viscosity of solvent-free condensates of silane 31 and MPTS.

The organic-inorganic polymer hybrids consisting of carbon-carbon and siloxane chains were prepared by radical polymerization of vinyltrimethoxysilane (VTS) and 3-methacryloxypropyltrimethoxysilane (MAS) followed by hydrolytic polycondensation. Polyvinyltrimethoxysilane (PVTS) and poly(3-methacryloxypropyltrimethoxysilane) (S-PMA) with various molecular weights Mw=3900–64800 were prepared by polyaddition of VTS and MAS, respectively. PVTS and S-PMA provided transparent and flexible free-standing films and coating films. With increasing carbon-carbon chain length, the elasticity of the films increased, while the tensile strength and Young's modulus decreased. The adhesive strength of the coating films on organic substrates was particularly dependent on the solubility parameter, polarity and crystallinity of each substrate. The pencil-hardness of coating films was clearly increased with increasing degree of condensation of sila-functional group in PVTS and S-PMA.

Amorphous 11B31,9C36,8N31,3 ceramic samples were produced by thermolysis of poly(borosesquicarbodiimide) of idealized formula [B2(NCN)3]n at 1100°C in inert gas atmosphere. Small angle scattering (SAS) experiments reveal, that the as-obtained ceramics are chemically inhomogeneous. Using small angle neutron and X-ray scattering measurements, the temperature dependency of the medium range order was investigated. The SAS curves show a strong temperature dependence of the Guinier-radius (RG) of the scattering regions. Contrast variation by X-ray and neutron diffraction shows that the observed SAS signal is caused by amorphous BC2N enclosing amorphous boron-nitride segregations. The fact, that the measured invariant remains constant over the whole temperature range supports the view of complete phase separation.

A new technique in surface modification is presented where chain growth polymerizations are initiated from tethered ruthenium alkylidene catalysts and organic-inorganic hybrid materials are produced. This approach provides nearly complete control over the polymer layer at the organic-inorganic interface with independent control over the chain length and grafting density. Hybrid particles are characterized using standard methods, i.e. NMR and transmission IR.

The sol-gel chemistry in low-temperature conditions can be used to produce organicinorganic materials nanocomposite from the in-situ formation of silica-rich phase in a polymer matrix. Different synthetic routes have been proposed: i) hydrolysis and condensation reactions of silane end capped oligomers, ii) polymerization of hydroxyethyl methacrylate, HEMA in presence of preformed functionalized silica nanoparticles, and iii) simultaneous hydrolysis and condensation of tetraethoxysilane and polymerization of hydroxyethymeth-acrylate.

Rheological investigations made during the polymerization of these three systems display many differences. Time for gelation was chosen as the time at which the loss factor, tanδ is independent on the testing frequency, or the time at which the system displays an elastic response. Vitrification phenomenon is associated with a tanδ peak. In some cases vitrification of the inorganic-rich phase interfered with the observation of gelation and the appearance of a non soluble fraction in a good solvent like tetrahydrofurane can help for attribution.

During radical chain-polymerization of HEMA a classical Trommsdorff-effect was observed. It can be at the same time than the macrogelation in the case of neat HEMA or delayed by the presence of grafted SiO2 nanoparticles. During simultaneous synthesis of inorganic and organic phases, vitrification of the inorganic-rich phase occured just after macrogelation of the system.

Final morphologies are strongly dependent on the occurrence of these different structural transformations.

Sol-gel processing of materials is plagued by shrinkage during polymerization of the alkoxide monomers and processing (aging and drying) of the resulting gels. We have developed a new class of hybrid organic-inorganic materials based on the solventless ring-opening polymerization (ROP) of monomers bearing the 2,2,5,5-tetramethyl-2,5-disilaoxacyclopentyl group, which permits us to drastically reduce shrinkage in sol-gel processed materials. Because the monomers are polymerized through a chain growth mechanism catalyzed by base rather than the step growth mechanism normally used in sol-gel systems, hydrolysis and condensation products are entirely eliminated. Furthermore, since water is not required for hydrolysis, an alcohol solvent is not necessary. Monomers with two disilaoxacyclopentyl groups, separated by a rigid phenylene group or a more flexible alkylene group, were prepared through disilylation of the corresponding diacetylenes, followed by ring closure and hydrogenation. Anionic polymerization of these materials, either neat or with 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane as a copolymer, affords thermally stable transparent gels with no visible shrinkage. These materials provide an easy route to the introduction of sol-gel type materials in encapsulation of microelectronics, which we have successfully demonstrated.

Dendrimer metal nanocomposites are novel hybride materials that display unique physical and chemical properties as a consequence of the atomic/molecular level dispersion of inorganic and organic molecules. In their synthesis, dendrimers are used as templates to pre-organize metal ions followed by an in-situ reduction, which will immobilize and stabilize atomic domains of the reaction product(s). Size, shape, size distribution and surface functionality of these nanocomposites are determined and controlled by the dendritic macromolecules and may also be influenced by the encapsulated compounds. Solubility of these molecular nanocomposites is controlled by the polymer. Thus, it is possible to solubilize conventionally insoluble inorganic compounds in water or other solvents using dendritic hosts. Conceptually, these materials have enormous potential for applications such as catalysts or molecular devices.

In this work, surface-modified poly(amido-amine) dendrimers were used to prepare {Cu(0)-PAMAM}, {Ag(0)-PAMAM} and {Au(0)-PAMAM} dendrimer-metal nanocomposites containing stable and solvent soluble zero valence metals. Characterization of the resulting nanocomposites has been carried out by TEM, UV-visible spectroscopy, and scattering techniques. Depending on the chemistry of ion preorganization in the dendrimer, internal (“I”), external (“E”) and mixed (“M”) type nanocomposite structures could be identified according to the varying location of the actual metal content.

The effect of structural differences was found to be reflected in the optical properties of the nanocomposites.

A novel hollow fiber silica was created by the use of the fibrous structures of an organic gel as a template. Its inner diameter ranged from 10 to 200 nm and the outer diameter ranged from 50 to 300 nm. A dichloromethane solution of an organic gelator was mixed with the silicate solution, TEOS/water/catalyst (acetic acid or benzylamine)/solvent (acetic acid or alcohol), which was gelated by the organic gelator. Subsequently, the resultant solution was evaporated in vacuo until the dichloromethane was removed to give a turbid gel. The SEM images of the product showed well-grown fibrous structures. After calcination, it was clearly found by TEM images that these fibers have a tubular structure. The most favorable gelator to form hollow fiber silica is one that has a cationic charge within the molecule, for example, a quaternary ammonium halide salt or a crown ether including a metal cation. In this study, the gel-forming segment of the gelator was a cholesterol derivative. Since the propagation species of silicate in the solution of acetic acid or benzylamine are considered to be anionic, the electrostatic interactions may be important for adsorption of silica onto the template fibers.

The precise pore sizes defined by crystalline zeolite lattices have led to intensive research on zeolite membranes. Unfortunately zeolites have proven to be extremely difficult to prepare in a defect-free thin film form needed for membrane flux and selectivity. We introduce tetrapropylammonium TPA (a structure directing agent for zeolite ZSM-5) into a silica sol and exploit the development of high solvation stresses to create templated amorphous silicas with pore apertures comparable in size to those of ZSM-5. 29Si and 2H NMR experiments were performed to evaluate the efficacy of our templating approach. The 29Si NMR spectrum of the silica matrix was observed by an intermolecular cross-polarization experiment between the 1H nuclei of TPA and the 29Si nuclei in the silica matrix. The efficiency of the cross-polarization interaction was used to investigate the degree to which the matrix formed a tight cage surrounding the template molecule. Bulk xerogels, prepared by gelation and slow drying of the corresponding sols, exhibited only weak interactions between the two sets of nuclei. Thin film xeorgels, where drying stresses are greater, resulted in significantly increased interactions. Analogous materials were prepared using fully deuterated TPA. The 2H NMR wideline spectra consisted of a partially narrowed resonance, corresponding to template molecules which were undergoing restricted rotational motion, and an isotropically narrowed resonance, corresponding to molecules which were undergoing rapid rotational motion. The number of isotropically rotating template molecules decreased for the thin film specimens, consistent with improved templating of amorphous silica by TPA.

The thermosetting mechanism of an organosilicon polymer containing carborane has been studied utilizing the 13and 29Si solid-state NMR method. The polymer having C≡C bonds in the main chain and CH═CH2, Si-H bonds, and carborane in the bulky side chain, shows a very highly thermal stability in air by curing. From 13C and 29Si NMR spectra of the polymer, it was found that the intermolecular cross-linking reactions of the polymer was due to (1) the diene reaction between Ph-C≡C and C≡C and (2) the addition reaction between side chain terminal and Ph-C≡C and between CH═CH2 and Si–H, and a very highly thermal stable structure is formed.

Thermosets and ceramic chars were characterized for three polymeric materials consisting of diacetylene-siloxane repeat units, DaS, diacetylene-siloxane-carborane-siloxane repeat units, DaSCS, and a 90/10 copolymerization. The goal was to incorporate the known thermo-oxidative stability of the siloxane-carborane elastomers into high performance thermosets and ceramic chars. The DaSCS thermoset has excellent thermo-oxidative stability as determined by a low weight loss and tough residue after annealing 100 hours in air at 316°C, however the glass transition is a low 94°C. DaS and 90/10 thermosets do not undergo glass transitions below 350°C and have low weight losses on thermo-oxidative aging, however the residue was quite brittle. The much higher carborane content in DaSCS also seems to help in ceramic char formation. All polymers had similar char yields to 800°C, whereas DaSCS solidified to a 15% denser ceramic.

In this paper, we introduce a new approach for altering the properties of bridged polysilsesquioxane xerogels using post-processing modification of the polymeric network. The bridging organic group contains latent functionalities that can be liberated thermally, photochemically, or by chemical means after the gel has been processed to a xerogel. These modifications can produce changes in density, solubility, porosity, and or chemical properties of the material. Since every monomer possesses two latent functional groups, the technique allows for the introduction of high levels of functionality in hybrid organic-inorganic materials. Dialkylenecarbonate-bridged polysilsesquioxane gels were prepared by the sol-gel polymerization of bis(triethoxysilylpropyl)carbonate (1) and bis(triethoxysilylisobutyl)-carbonate (2). Thermal treatment of the resulting non-porous xerogels and aerogels at 300–350°C resulted in quantitative decarboxylation of the dialkylenecarbonate bridging groups to give new hydroxyalkyl and olefinic substituted polysilsesquioxane monolithic xerogels and aerogels that can not be directly prepared through direct sol-gel polymerization of organotrialkoxysilanes.

Polymerization of organotrialkoxysilanes is a convenient method for introducing organic functionality into hybrid organic-inorganic materials. However, not much is known about the effects of the organic substituent on the porosity of the resulting xerogels. In this study, we prepared a series of polysilsesquioxane xerogels from organotrialkoxysilanes, RSi(OR′)3, with different organic groups (R = H, Me, Et, dodecyl, hexadecyl, octadecyl, vinyl, chloromethyl, cyanoethyl). Polymerizations of the monomers were carried out under a variety of conditions, varying monomer concentration, type of catalyst, and alkoxide substituent. The effect of the organic substituent on the sol-gel process was often dramatic. In many cases, gels were formed only at very high monomer concentration and/or with only one type of catalyst. All of the gels were processed as xerogels and characterized by scanning electron microscopy and nitrogen sorption porosimetry to evaluate their pore structure.

The reaction of readily available Cy8Si8O12 (3) with triflic acid (TfOH) can produce two different ditriflates derived from controlled cleavage of Si-O-Si linkages. These ditriflates can be subsequently hydrolyzed to four different incompletely condensed silsesquioxanes, which are attractive precursors to hybrid inorganic/organic materials.

Monolithic silica aerogels modified by functional organic groups were prepared by basecatalyzed sol-gel processing of Si(OR)4 / R'Si(OMe)3 mixtures (R' = organofunctional group), followed by drying of the wet gels with supercritical CO2. When the functional organic group has only weakly or no basic properties, the microstructure of the obtained aerogels is similar to that of an unmodified silica aerogel prepared under the same conditions and quite independent of the kind of functional group. The experimental findings are explained by a two-stage process in which the R'Si≡ units condense to a pre-formed gel network obtained by hydrolysis and condensation of Si(OR)4. An increasing portion of R'Si(OMe)3 has the same effects on the hydrolysis and condensation reactions as decreasing the bulk density of an unmodified silica aerogel and the same structural consequences as increasing the water / silane ratio and the catalyst concentration acting on Si(OR)4. This leads to larger primary particles and, associated with that, smaller specific surface areas. The two-stage process is not observed when R' contains a strongly basic substituent such as NH2 or NHCH2CH2NH2. The structural parameters indicate that in these cases both R'Si(OMe)3 and Si(OR)4 are involved in the built-up of the gel network. This can be explained by extensive hydrogen bonding between the amino groups and silanol groups.

2,2,4,4,6,6-Hexachlorocyclotriphosphazene was modified by nucleophilic substitution to obtain building blocks for organic polymers and siloxane networks. 2,2,4,4,6,6-Hexachlorocyclotriphosphazene was substituted with functional groups to enable atom transfer radical polymerization (ATRP) as well as silicon alkoxide as precursors for the sol-gel process. ATRP was carried out with methyl acrylate followed by a chain extension with iso-bornyl acrylate to obtain new thermoplastic elastomers. The sol-gel process was carried out with acid, base and fluoride catalysts and the resulting materials were compared by TGA and DSC measurements.

Organic-inorganic hybrid nanocomposite materials of poly(methyl methacrylate) (PMMA) and organically-modified silicate (B34) systems have been prepared via melt intercalation with variation of tacticity and molecular weight as the main molecular variables. Only two of the PMMA samples (with the lowest glass transition temperatures) were able to undergo large-scale intercalation into B34, as seen by X-ray diffraction (XRD) and Infrared spectroscopy. The saturation weight ratio of PMMA to B34 was about 25:75 (wt%), deduced by a controlled differential scanning calorimetry (DSC) experiment. Two new absorption bands of PMMA-B34 hybrid in Fourier transform-infrared spectrometry (FTIR) were demonstrated for first time in this system and show a change in molecular interaction of bulk and intercalated PMMA. The degradation temperature of the PMMA-B34 hybrid is higher than that of PMMA alone, or a physical mixture of PMMA and silicate under an air or a nitrogen flow.