Polyhedral Oligomeric SilSesquioxanes (POSS) are structurally well defined cage-like molecules represented by the generic formula (RSiOl.5)n. POSS compounds possess a unique hybrid composition with an oxygen to silicon ratio of 1.5, intermediate between that for silica and silicone. An entire monomer catalogue (chemical tree) of hybrid POSS-based reagents suitable for polymerization and grafting reactions has been developed from R7Si7O9(OH)3 and related precursors. POSS reagents containing no more than one or two reactive groups enable the preparation of hybrid materials with desirable physical properties such as thermoplasticity, and elasticity. An overview of the synthesis of POSS monomers and thermoplastic POSS-acrylic polymers is given. The thermal and physical properties for POSS-acrylic monomers, homopolymers, copolymers, and blends with poly(methylmethacrylate) are described.

For the preparation of inorganic-organic hybrid materials, synthesis processes have been developed to fabricate so-called hybrid sols, which contain an inorganic core (ceramic or glass) with nano-scale dimensions surface modified by organic groupings. These groupings have been reacted to the particle surface either by amino functional silanes (e.g. in case of iron oxide nanoparticles for amino group containing silanes) reacting with aliphatic acids to make surfaces unreactive and reduce the particle-to-particle interaction by acids, or silanes with polymerizable groupings reacted with organic monomers. In the paper a summary of the recent work and the development of structural models is given. Moreover, it could be shown that surface charges can be generated in the particles within already gelled systems and thus, particles can be transported by electric fields to form gradient index materials.

We have taken a unique approach to the synthesis and study of hybrid organic/inorganic materials. Our method involves synthesizing nano-size inorganic P1R7Si8Ol2 clusters which contain seven inert “R” groups for solubility and only one functional “P” group for polymerization. This strategy permits the synthesis of melt processable, linear hybrid polymers containing pendent inorganic clusters and allows us to study the effect these clusters have on chain motions and polymer properties. The synthesis of styrene-based polyhedral oligomeric silsesquioxane (POSS) macromers, their free radical homopolymerization and copolymerizations with varying amounts of 4-methylstyrene, and analysis of the effect of the pendent POSS group is presented. All of these polymers decompose under nitrogen between 365 and 400 °C, and the glass transitions for these materials vary from around 110 °C up to the decomposition point. Both Tdec and Tg increase with increasing POSS content. The shorter the spacer unit between the POSS group and the polymer chain the higher the Tg. Interestingly, a slight change in the inert “R” groups on the POSS cluster has a large effect on the glass transition indicating that POSS-POSS interactions have an effect on chain mobility.

Under acidic sol-gel polymerization conditions, 1,3-bis(triethoxysilyl)-propane 1 and 1,4-bis(triethoxysilyl)butane 2 were shown to preferentially form cyclic disilsesquioxanes 3 and 4 rather than the expected 1,3-propylene- and 1,4-butylene-bridged polysilsesquioxane gels. Formation of 3 and 4 is driven by a combination of an intramolecular cyclization to six and seven membered rings, and a pronounced reduction in reactivity under acidic conditions as a function of increasing degree of condensation. The ease with which these relatively unreactive cyclic monomers and dimers are formed (under acidic conditions) helps to explain the difficulties in forming gels from 1 and 2. The stability of cyclic disilsesquioxanes was confirmed with the synthesis of 3 and 4 in gram quantities; the cyclic disilsesquioxanes react slowly to give tricyclic dimers containing a thermodynamically stable eight membered siloxane ring. Continued reactions were shown to perserve the cyclic structure, opening up the possiblity of utilizing cyclic disilsesquioxanes as sol-gel monomers. Preliminary polymerization studies with these new, carbohydrate-like monomers revealed the formation of network poly(cyclic disilsesquioxanes) under acidic conditions and polymerization with ring-opening under basic conditions.

A new synthesis of the macro-cation {(BuSn)12O4(OH)6}2 is described from commercially available and easy to handle BuSnO(OH) and p-toluene sulfonic acid. A crystalline compound, {(BuSn)12O4(OH)6}(O3SC6H4CH3)2.C4H8O2, is obtained. It can react with tetramethylammonium hydroxide to yield the more versatile composition: {(BuSn)12O4(OH)6}(OH)2. The macro-cations are then used as nanobuilding blocks and assembled in rosary-like structures by carboxyterminated poly(ethyleneglycol). The resulting system can be pictured as hybrid organic-inorganic alternated block co-polymers. Characterizations were performed with 119Sn NMR (solution and solid state), 13C CP-MAS NMR and FT-IR.

Unique synthetic approaches for the synthesis of homogeneously dispersed and highly loaded aluminum nitride (AIN) / polyimide (PI) nanocomposites have been developed. The effective interactions at the solid-liquid interface during the preparation of stable dispersions of ceramic/polymers have been investigated. In particular, the surface chemical composition of the nanoparticles has been analyzed. Characteristic model reactions on the surface have been carried out, which revealed the mechanisms for the deagglomeration and stabilization of nanoparticles via chemisorption reactions. Moreover, compared to other synthetic approaches, this method demonstrates the capability of preparing extremely highly loaded nanocomposites and being applicable to a wide range of materials. The thermal and mechanical properties of the A1N/PI nanocomposite have also been studied.

A novel family of inorganic-organic copolymers (ORMOCER*s) derived from urethaneand thioether(meth)acrylate alkoxysilanes has been successfully exploited for a variety of diverse applications. In order to widen the range of applications an additional functionality (carboxy group) has been incorporated in this silane type. Conventional sol-gel processing facilitates the formation of an inorganic “Si-O-Si”-network via hydrolysis and polycondensation reactions of alkoxysilyl moieties and in addition, the (meth)acrylate groups are available for radically induced polymerization to obtain a complementary organic polymeric structure. The presence of a carboxy group would appear to have great potential for a range of diverse areas of application, such as an internal catalyst for the sol-gel process, complexation of elements such as Zr and Ti, increasing the adhesion to various substrates and modification of solubility. A number of novel silanes and their syntheses will be described in this paper.

Terephthalate anions have been incorporated as charge-balancing species inside the layers of Mg-Al containing layered double hydroxides (LDHs). The ease of incorporation as well as the orientation of the guest species has been studied as a function of the Mg/Al ratio. The orientation of the guest as a function of temperature and degree of hydration has also been studied using powder X-ray diffraction. Molecular dynamics simulations, using an NPT ensemble, have been performed and good agreement between experimental and simulated data has been obtained.

A new class of epoxy-clay nanocomposites have been prepared from alkylammonium exchanged fluorohectorite clays. These nanocomposites have usually large and regular basal spacings up to 105 Å platelet separation. The extra large separation of the clay nanolayers results in reinforcement of the polymer matrix, the reinforcing effect being comparable to that of disordered phased nanocomposites. It is now possible to define two general classes of exfoliated clay nanocomposites, namely those with long range nanolayer ordering, and those with little or no long range ordering. Long range ordering is indicated by the XRD patterns that have multiple 001 harmonies whereas disordered composites exhibit little or no 001diffraction. Regardless of the presence of X-ray Bragg diffraction, exfoliated polymer-clay nanocomposites form when adjacent clay nanolayers are separated by a distance that precludes the possibility of interlayer communication through the association of galleries cations.

The use of dynamic light scattering to monitor the dispersion of clay platelets in a polymer matrix is described. The dispersed clay/polymer composite was prepared by joining surfactant monomers to synthetic hectorite clay platelets by a cationic exchange reaction and subsequently polymerizing with acrylamide. Dispersion of the organically modified clay in aqueous solution was facilitated by preparing a clay surfactant precursor suspension with a surfactant concentration significantly above the clay cation exchange capacity. At lower surfactant concentrations the clay does not disperse but instead forms large polydisperse aggregates unsuitable for making homogeneous composites. The presence of these aggregates could not be found in an x-ray powder diffraction scan but were clearly detected using dynamic light scattering.

Hybrid organic-inorganic composites were prepared by precipitating silica into hydroxypolybenzoxazole (HPBO) and sulfopolybenzobisthiazole (SPBT) polymers, with interfacial bonding between the phases improved by use of isocyanatopropyltriethoxy silane and N,N-diethylaminopropyltrimethoxy silane, respectively. The resulting materials were characterized with regard to their transparency, silica particle distribution, tensile modulus and tensile strength, thermal stability, and tendency to absorb water.

A new family of hybrid inorganic/organic network materials – the star gels – has been synthesized from single component molecular precursors. The starting materials comprise an organic core with multiple flexible arms which terminate in network-forming trialkoxysilane groups. The core can be a single silicon atom, linear disiloxane segment or ring system. With at least 12 alkoxysilane groups per molecule, gelation rates in aqueous or formic acid media can be extremely high, but can be attenuated several orders of magnitude by choice of solvent system. The degree of intramolecular condensation of these molecules has been assessed via mass spectrometric techniques. Transparent glasses which show brittle fracture but high levels of toughness have been generated from this family of precursors. The materials do not show plastic deformation even under compressive stress of 350 MPa. No evidence for open porosity in the glasses has been obtained. The organic content of the networks can be increased by lengthening the arms; the inorganic content can be increased via co-hydrolysis with simple tetraalkoxysilanes such as TEOS. Species with longer arms lead to glasses with higher coefficients of thermal expansion.

A model is described which incorporates hydrolysis pseudo-equilibrium to quantify the evolution of silicon site distributions in sol-gel polymerization up to higher conversions than previously possible. 29Si nuclear magnetic resonance spectroscopy data are used 1) to provide a means of recognizing hydrolysis pseudo-equilibrium and 2) to provide examples where different substitution effects on condensation rate coefficients caused by branching are observed. Extension of the model to copolymerization is discussed.

17O NMR in solution using enriched water as reactant has been used to investigate cohydrolysis of dimethyldiethoxysilane and tetraethoxysilane, as well as methyltriethoxysilane and tetraethoxysilane. Co-condensation reactions were clearly identified in both systems : the amount of oxo bridges between the two kinds of Si units is rather large, and those bridges are stable during aging, which favor a good chemical homogeneity in the final gels. This last point was investigated on the related dried gels by 29Si Magic Angle Spinning NMR, using Cross-Polarization (CP) technique that allows to probe the local environment of the various Si sites through 29Si-1H dipolar interactions.

An amphoteric surfactant, cocamidopropyl betaine, was used for the synthesis of mesoporous zirconia. The carboxylate functionality of the surfactant permitted strong bonding with soluble zirconium species, while the quaternary ammonium group ensured large headgroup area and high solubility under acidic conditions. An amphoteric co-template [betaine, or (carboxymethyl)trimethylammonium hydroxide] improved uniformity of the hexagonal mesophase. Transmission electron microscopy (TEM) of the as-synthesized zirconium sulfate mesophase indicated hexagonal mesostructure, and low-angle X-ray diffraction (XRD) showed a 41 Å primary d-spacing and two higher order reflections of a hexagonal lattice. High surface area zirconia was produced by controlled base treatment of the hexagonal mesophase with sodium hydroxide, followed by calcination. TEM and XRD indicated that the mesostructure was stable to 350°C.

Titanium and aluminium alkoxide derivatives with polymerizable ligands such as 2- (methacryloyloxy)ethylacetoacetate (HAAEMA), oleic acid and geraniol (HOGE) have been obtained. The various compounds have been characterized by FT-IR and NMR 1H. Copolymerization with styrene and divinylbenzene affords porous doped organic materials which have been characterized by scanning electron microscopy (SEM), elemental analysis, density measurements.

The isocyanate chemistry has been used to prepare, without adding any solvent, organic-rich hybrid O/I systems. α–ω hydroxy-terminated prepolymers (soft segments, denoted SS) can be end-capped with γ-isocyanato propyl triethoxy silane (γ-IPS), or previously reacted with a diisocyanate (DI) and then end-capped with y-amino propyl triethoxy silane (γ-APS), or with γamino propyl methyl diethoxy silane (γ-APMDES). With this second pathway, a double distribution of molecules is present. The aim of this work is to investigate the morphologies and structural properties of different organic-rich hybrid organic/inorganic materials. Two types of α-ω hydroxy prepolymers have been used : hydrogenated polybutadiene, HPBD, and polycaprolactone, PCL.

The inorganic phase is obtained through the hydrolysis and condensation of the silane groups under acidic conditions and with [H2O]/Si = 3. Assuming a complete conversion of SiOH groups, the SiO2 content never exceed 10% wt. The extent of crosslinking is estimated by the soluble fraction able to be extracted by tetrahydrofurane. Times for gelation were obtained by rheological measurements and/or from the appearance of insoluble fractions. In-situ small angle X-ray scattering (SAXS) measurements show that phase separation between an organic-rich phase and an inorganic-rich one can appear before or after gelation depending on the acid catalyst concentration and the nature of SS.

The nanometric silica-rich particles in the final morphologies, after a post-cure at 150°C, were also studied by means of SAXS measurements. Viscoelastic measurements show one or two main relaxation peaks depending on the phase separation process during reaction and the polarity of the initial SS. However for full crosslinked SS/γ-IPS hybrid networks, the relaxed modulus does not depend on SS nature and it is well described by the affine network theory. Silica particles have a small size and probably a high functionality in elastically active network chains (EANC). The fully cured SS/DI/silane hybrid networks equilibrium moduli are higher than SS/γ-IPS one. This can be understood if some silane end-linked DI participate to the EANC.

Ongoing work in our laboratories continues to demonstrate the unique properties that can be developed by the generation of a glassy semi-interpenetrating network (SIPN) within an elastomeric-based hybrid organic-inorganic composite. The hybrids are synthesized by the acid catalyzed sol-gel-processing of triethoxysilane end-capped poly(tetramethylene oxide) (PTMO) and tetraethoxysilane (TEOS) in an alcoholic solution. The SIPNs are then created by swelling these hybrids with methacrylic acid (MAA) and then gamma-polymerizing the monomer in-situ. The resulting materials exhibit excellent optical transparency and significantly improved toughness. This paper reports on the effect of inorganic loading upon the mechanical properties of acid catalyzed hybrid composites. The results demonstrate that as the amount of TEOS added to the sol prior to gelation increases the elongation-to-break decreases and the stress-to-break increases. Similarly, the post-yield stress drop and post-yield elongation prior to strain hardening increase with increasing inorganic loading. Atomic force microscopy and small angle X-ray scattering data is presented which substantiates the morphological model developed to explain the mechanical response.

Polyimide-silica hybrid materials were prepared via a modified sol-gel, high pressure-thermal polymerization procedure. Precursor monomer salts were made from ethanol soluble 2,5- diethoxycarboxyl terephthalic acid (p-PME) and either a disiloxanediamine, an aliphatic diamine (1,9 diaminononane) or combinations of the two. Solutions of tetramethoxysilane (TMOS) and monomer salt were transformed into a gel, dehydrated, and the resulting powders were subjected to high pressure and thermal polymerization and transformed into a polyimide-silica composite. By varying the TMOS content, and/or the siloxane to aliphatic diamine ratio., composites of 0 to 100 wt% SiO2 were made. The silica morphology changed significantly with siloxane/aliphatic PI ratio. Reaction mechanisms, thermal and physical properties and composite morphologies are discussed.

Sol-gel derived Poly(methyl methacrylate)-titania hybrid materials were synthesized by using acrylic acid or allyl acetylacetone (3-allyl-2,4-pentanedione) as coupling agents. Titanium butoxide modified with acrylic acid (or titanium isopropoxide modified with allyl acetylacetone) was hydrolyzed to produce a titania network, and then poly (methyl methacrylate) (PMMA) chains formed in situ through a radical polymerization were chemically bonded to the forming titania network to synthesize a hybrid material. Transparent hybrid materials with different contents of titania were achieved. With the increase of the titania content, the colors of the products changed from yellow to dark red. The synthesis process was investigated step by step by using FTIR spectroscopy, and the experimental results demonstrated that acrylate or acetylacetonato groups bound to titanium remain in the final hybrid materials. The thermal stability of the hybrid materials was considerably improved relative to pure PMMA. Field emission scanning electron microscopy (FE-SEM) analyses showed the hybrid materials are porous and pore diameters vary from 1 Onm to I 00nm. The hybrid materials using allyl acetylacetone as the coupling agent exhibited thermochromic effects that both pure PMMA and titania do not have.