A new family of materials that synergistically combine the attributes of both organic and inorganic properties for use in organic light emitting diodes (OLEDs) is presented. The hybrid materials are based on 3-D inorganic cores of octavinylsilsesquioxanes (OVS). The resultant materials have high Tg's (120–210°C), are formed from minimal step/high yield reactions and readily available starting reagents, are monodisperse (PDI<1.1), can be highly purified via common chroma-tographic techniques, and form defect-free amorphous films via spin-dip coating. For example TPD is known for its good hole injection/transport properties in OLED applications but suffers from a low Tg (65°C). TPD-OVS hybrid material has a Tg of 142°C while maintaining similar injection/transport properties to TPD. Photoluminescence analysis of the hybrid thin film reveals: 1) a 30 nm blue shift versus their dilute solution counterparts; and 2) 5 hour annealing cycles to within 10°C of their Tg show no indication of eximer formation (no red shift) that often causes reduced efficiencies in polymer LEDs.

The basic tetrahedra of silica are readily assembled into eight cornered cages known as cubic silsesquioxanes ([RSiO1.5]8). Silsesquioxane cubes represent one of the smallest possible units of ceramic silica. The corners of these nanometer-sized ceramic cubes are readily functionalized with reactive groups and incorporated into organic polymers. In this work, we characterize the structures that result from varying the length of the flexible organic segments used to connect the cubes in a series of hybrid network materials. For very short organic segments, steric hindrances inhibit high degrees of network conversion and the resulting network is very inhomogeneous. As the length of the flexible organic segment increases, the added degrees of freedom allow a more ‘ordered’ glassy material to evolve. If the length of the organic segment becomes very long in comparison to the size of the cube, a disordered polymer-like network is obtained.

Sixty−70 μm diameter preceramic fibers, extruded from THF solutions containing 1:2:3 stoichiometric mixtures of yttrium, barium, and copper carboxylates, were pyrolytically transformed into ceramic fibers using controlled heating schedules and reactive atmospheres. The objectives of the work reported here were to identify appropriate processing conditions such that during pyrolysis the preceramic fibers would (1) eliminate the organic ligands without pore or void formation, (2) reach full density with a controlled grain size, and (3) form orthorhombic phase, 123 fibers with reasonable mechanical properties. The mechanisms of organic ligand decomposition and loss were examined using mass spectral fragmentation and TGA. Microstructural and phase evolution were correlated with heating schedules and atmospheres, using XRD, DTA, SEM, and limited flux exclusion studies. The mechanisms of decomposition of the spinnable mixtures suggest intermolecular rather than intramolecular decomposition pathways. Different pyrolysis atmospheres were also examined to explore methods of controlling the degradation process. Slow pyrolysis in air followed by oxygen anneals appears to give superior fibers in terms of controlled grain size and phase. The pyrolyzed fibers exhibit the appropriate orthorhombic phase according to x-ray powder diffractometry. Preliminary flux exclusion measurements demonstrate that the fibers are superconducting although the measured δTc is not exceptional.

Polymethylsilane (-[MeSiH]x-) synthesized from a single step catalytic polymerization of methylsilane (MeSiH3), provides a new route to near stoichiometric, microcrystalline silicon carbide fibers. The final composition is controlled by selected additives. The entire process simply contains 3 simple steps: (1) a single step synthesis of polymer precursor, (2) precursor fiber spinning, and (3) a single step pyrolytic conversion to target ceramic fibers.

We have previously reported the synthesis of cordierite polymer precursors directly from MgO, SiO2 and alumina.1 Removal of organics at 400°C in air and/or in oxygen gave amorphous, atomically mixed, oxide powders with surface areas of 250-400 m2/g. It is possible to convert these high surface area oxide powders to Mg-Si-Al-O-N powders by heating in a flowing NH3 atmosphere. The effects of selected processing conditions on nitrogen incorporation, in a set of well defined oxide powders, were examined. The powders are nitrided in flowing NH3, at temperatures of 700-1200°C, to obtain N contents of up to 5 atomic percent.

Working principles are developed as guidelines for the selection and/or design of organometallic polymers for processing fiber precursors to metal oxide fibers. These principles form the basis for the selection of metal carboxylate preceramics as an optimal approach to processing yttrium barium cuprate (123) ceramic superconducting fibers. A variety of candidate yttrium, barium, calcium, strontium, bismuth, and copper metal carboxylates were synthesized. Solubility and empirical rheology tests were conducted to screen these compounds to choose spinnable precursor systems. Simple extrusion studies confirmed that THF solutions of mixtures of yttrium, barium, and copper isobutyrates with some quantity of barium 2-ethyl-hexanoates can be used to successfully form 60–70 μm diameter 123 precursor fibers.

The reaction of SiO2 with basic magnesium compounds, in the presence of excess ethylene glycol, provides access to the hexacoordinate silicate complex, MgSi(OCH2CH2O)3. Alkali metal hydroxides provide access to pentacoordinate silicates of the type M2Si2(OCH2CH2O)5, where M = Li, Na, K, and Cs. Alumina also reacts with alkali metal hydroxides and ethylene glycol to give compounds of the type MAI(OCH2CH2O)2. HCl neutralization of the alkali metal silicates and aluminates provides the neutral metal glycolates of Si and Al. Stoichiometrically correct mixtures of these complexes form homogeneous, cordierite precursor solutions that are potentially useful for forming films, fibers and membranes of cordierite. These polymer-like materials can be heated directly in air to generate first α-cordierite and then µ-cordierite. Hydrolysis and condensation reactions, which occur in sol-gel processing, are not required. The phase transformations and chemical changes that occur during pyrolytic transformation of the preceramic materials to their target ceramic products were characterized. Methods developed during the course of these studies led to the development of heating schedules wherein well crystallized g.-cordierite could be formed at 850 °C.

Bimetallic glycolato silicates of the form M2 Si2(OCH2CH2O)5 where M is an alkali metal, can be synthesized directly from SiO2, ethylene glycol and MOH. Further reaction with HO(CH2CH2O)4H, PEG4, transforms these compounds into rheologically useful polymers. These polymers offer considerable potential for processing novel silicate glass shapes, e.g. thin films, fibers and membranes, from relatively inexpensive precursors materials. In this paper, we describe pyrolysis studies on the model compound Li2 Si2(OCH2CH2O)5 as a prelude to determing the utility of the polymeric precursors. These studies delineate the effects of temperature on the decomposition processes whereby the glycolato silicate transforms into almost phase pure, crystalline Li2O-2SiO2. This work is contrasted with previous pyrolysis studies on K2 Si2(OCH2CH2O)5.

A variety of anhydrous Y, Ba and Cu carboxylates were synthesized and screened for utility as spinnable precursors to 123 superconducting fibers. Simple extrusion studies demonstrate that THF solutions of mixtures of Y, Ba and Cu isobutyrates with some Ba 2-ethyl- hexanoate can be used to form 70 μm dia. precursor fibers. Following a curing at 150°C for 24–48 h, pyrolysis of these fibers in air to 900°C, with controlled heating rates, gives dense, flexible ceramic fibers 15–20 μm in dia. These fibers have the appropriate orthorhombic phase. Flux exclusion measurements indicate the fibers are superconducting; but ΔTc is not optimal.

Polysilsesquioxanes,-[RSi(O)1.5 ]x-, exhibit many properties that are potentially quite useful for industrial applications. These properties include high temperature stability (−600°C in O2); good adhesion and, liquid crystal-like behavior for some derivatives. Moreover, [MeSi(O)l.5]x, polymethylsilsesquioxane has been used successfully as a precursor for the fabrication of carbon fiber/“black glass” (SiO2/SiC/C) composites and “black glass” fibers.

Current methods of preparation depend on hydrolysis of RSiCl3 or RSi(OR)3. Unfortunately, this approach leads to several products that are difficult to purify because polysilsesquioxanes exhibit a great propensity for forming gels. We describe here a simple catalytic approach to the synthesis of polymethylsilsesquioxane copolymers of the type -[MeRSiO].3[MeSi(O)1.5].7- where R - H, OMe, OEt, OnPr and OnBu. The R - H copolymer is produced by catalytic redistribution of -[MeHSiO]xoligomers using dimethyltitanocene, Cp2TiMe2 as the catalyst precursor.

Following catalytic redistribution, the resulting copolymer, -[MeHSiO].3[MeSi(O)1.5].7−, is reacted in situ with alcohols to produce -[Me(R'O)SiO].3[MeSi(0)1.5].7− (where R' - Me, Et, nPr and nBu) which serve as masked forms of the polymethylsilsesquioxane. These new copolymers have been characterized by 1H, 13C and 29Si NMR TGA and DTA. The NMR studies allow us to assign structures for the copolymer.

These new copolymers exhibit improved tractability. Their high temperature properties are all quite similar; although, the MeO-, EtO- and especially the nPrO- derivatives give much higher ceramic yields than expected.

Pyrolyses of a set of silicon and nitrogen substituted polysilazancs arc conducted under a set of standard conditions (5°C/min to 900°C in a nitrogen atmosphere). The apparent ceramic compositions and ceramic yields for pyrolyzed samples of the polysilazancs -[Ph(H)SiNH]x-, -[C6H13(H)SiNH]x-, -[Me(H)SiNH]x-, and -[H2SiNMc]x- arc determined. Preliminary conclusions concerning structure/reactivity relationships are discussed based on the pyrolysis results.

Characterization of the pyrolysis products of preceramic polysilazanes synthesized by reactions of the oligomer-[H2SiNMe]x in the presence of Ru3 (CO)12 catalyst has demonstrated that these polymers have great potential as precursors of Si3N4 for several applications. The polysilazanes studied are viscous liquids that can be converted to ceramic material with a yield of >65 wt %. The vitreous product contains regions of fully dense material and large cavities that indicate of considerable gas evolution. A preliminary pyrolysis sequence has been constructed based on a combination of TGA of the polymer, SEM investigation of the product, and mass spectroscopic analysis of the gases and heavy fragments released during conversion of the polysilazanes to ceramic material. This understanding of pyrolysis mechanisms will aid in developing even more effective polymeric precursors to Si3N4 and in optimizing pyrolysis procedures for a variety of useful appl ications.

A transition metal (e.g., Ru3 (CO)12, Pt/C) catalyzed process for Si-N bond formation is discussed that provides a new route to mono-, oligo-, and polysilazanes. The catalysts function by activating Si-H bonds in the pres-ence of ammonia. Polymeric silazanes can also be produced from oligomers in the presence of ammonia at low temperatures. This method allows us to control or modify the composition of the polysilazane during or after the polymeriza-tion. A variety of polysilazanes were prepared and converted to Si3 N4 with ceramic yields ranging from 55%-85%. By varying the monomers and reaction conditions, we can control the nitrogen and carbon content in the preceramic polymers, which enables us to obtain ceramic products that are primarily Si3N4and simultaneously minimizes the coproduction of SiC and C.