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Cross-condensation kinetics of organically modified silica sols

Description: The hydrolysis and self- and cross-condensation kinetics of the hybrid sol tetraethoxysilane and ethyltriethoxysilane were investigated by high resolution {sup 29}Si NMR spectroscopy. A kinetic model in which hydrolysis is reversible and condensation is irreversible was developed. The authors found excellent agreement between the product distributions measured by {sup 29}Si NMR spectroscopy and calculated by the model. The cross-condensation rates for each of the sols were intermediate to the condensation rates of the individual components. Calculations show that for these sols, the concentration of cross-condensed species is a weak function of the relative rates of self-condensation.
Date: June 1, 1996
Creator: Prabakar, S. & Assink, R.A.
Partner: UNT Libraries Government Documents Department

Morphology and phase composition of an amine cured rubber modified epoxy

Description: The sharpness of the interface between the matrix and the dispersed phase, the volume fraction of the dispersed phase, the distribution of particle sizes, and the concentration of epoxy in the dispersed phase were determined. Scanning transmission electron microscopy coupled with energy dispersive x-ray analysis revealed that the interface width is less than 500 A. Variation of the fraction of mobile hydrogens with temperature determined by nuclear magnetic resonance indicated that a small fraction of segments participated in mixing at the interface. Differential scanning calorimetry and nuclear magnetic resonance indicated that all the rubber precipitates as a discrete phase. The distribution of particles greater than 0.1 ..mu..m in diameter was measured, and the average diameter of these particles was found to be 0.8 ..mu..m. The particles larger than 0.1 ..mu..m accounted for approximately 50% of the total volume of dispersed phase. The epoxy concentration in the dispersed phase was determined using /sup 13/C nuclear magnetic resonance spectroscopy. This concentration was found to be less than that predicted if all the epoxy monomer units attached to the rubber molecules were present in the dispersed phase.
Date: January 1, 1980
Creator: Sayre, J.A.; Assink, R.A. & Lagasse, R.R.
Partner: UNT Libraries Government Documents Department

Synthesis of a C sub 60 -para-xylylene copolymer

Description: The preparation and purification of macroscopic quantities of buckminsterfullerenes of buckyballs has ignited an explosion of research into their physical and chemical properties, and a variety of strategies for preparing new fullerene-based materials. Free radical synthesis is an appealing approach for forming polymeric fullerene materials. We report a polymeric fullerene material prepared by reacting pure C{sub 60} with xylylene from the thermolysis of paracyclophane. Addition of xylylene to purple solution of C{sub 60} in toluene solution at {minus}78{degree}C resulted in an olive-green solution from which an insoluble brown powder precipitated upon warming to room temperature. Analyses of the powder by solid state {sup 13}C MAS NMR, IR, and thermal gravimetric analysis are consistent with a C{sub 60}-xylylene copolymer.
Date: January 1, 1991
Creator: Loy, D A & Assink, R A
Partner: UNT Libraries Government Documents Department

Investigation of hydrolysis and condensation in organically modified sol-gel systems: {sup 29}Si NMR and the INEPT sequence

Description: The spectral editing properties of the {sup 29}Si NMR INEPT heteronuclear transfer experiment have been utilized for the identification and characterization of hydrolysis and initial condensation products in methyltrimethoxysilane (MTMS) sol-gel materials. {sup 29}Si NMR assignments in MTMS are complicated by a small spectral dispersion ({approximately} 0.5 ppm) and two different {sup 29}Si-{sup 1}H J couplings. By using analytical expressions for the INEPT signal response with multiple heteronuclear J couplings, unambiguous spectral assignments can be made. For this organomethoxysilane the rate of hydrolysis was found to be very rapid and significantly faster than either the water or alcohol producing condensation reactions. The hydrolysis species of both the MTMS monomer and its initial T{sup 1} condensation products follow statistical distributions that can be directly related to the extent of the hydrolysis reactions. The role of the statistical distribution of hydrolysis products on the production and synthetic control of organically modified sol-gels is discussed.
Date: June 1, 1996
Creator: Alam, T.M.; Assink, R.A. & Loy, D.A.
Partner: UNT Libraries Government Documents Department

Characterization of aging in organic materials on atomic-, meso- and macro-length scales by {sup 13}C NMR spectroscopy

Description: A fundamental understanding of aging in an organic material requires that one understand how aging affects the chemical structure of a material, and how these chemical changes are related to the material`s macroscopic properties. This level of understanding is usually achieved by examining the material on a variety of length scales ranging from atomic to meso-scale to macroscopic. The authors are developing and applying several {sup 13}C nuclear magnetic resonance (NMR) spectroscopy experiments to characterize the aging process of organic materials over a broad range of length scales. Examples of studies which range from atomic to macroscopic will be presented.
Date: October 1, 1997
Creator: Assink, R.A.; Jamison, G.M.; Alam, T.M. & Gillen, K.T.
Partner: UNT Libraries Government Documents Department

Synthetic molecular receptors for phosphates and phosphonates in sol-gel materials

Description: Synthetic receptors for phosphates and phosphonates have been generated in SiO{sub 2} xerogels via a surface molecular imprinting method. The monomer 3-trimethoxy silylpropyl-1-guanidinium chloride (1) was developed to prepare receptor sites capable of binding with substrates through a combination of ionic and hydrogen bond interactions. HPLC studies and adsorption isotherms performed in water have found that molecular imprinting affords a significant improvement in K{sub a} for phosphate and phosphonate affinity over a randomly functionalized xerogel. Affinities for these materials offer about an order of magnitude improvement in affinity compared to analogous small molecule receptors reported in the literature. The xerogel matrix appears to participate in host-guest interactions through anionic charge buildup with increasing pH.
Date: December 1, 1997
Creator: Sasaki, D.Y.; Alam, T.M. & Assink, R.A.
Partner: UNT Libraries Government Documents Department

Probing oxidative degradation in polymers using {sup 17}O NMR spectroscopy

Description: Understanding the mechanism of oxidative degradation remains an important goal in being able to predict the aging process in polymer materials. Nuclear magnetic resonance (NMR) spectroscopy has previously been utilized to investigate polymer degradation, including both proton ({sup 1}H) and carbon ({sup 13}C) studies. These previous NMR studies, as well as other spectroscopic investigations, are complicated by the almost overwhelming signal arising from the native undegraded polymer. This makes the identification and quantification of degradation species at small concentrations difficult. In this note we discuss recent investigation into the use of oxygen ({sup 17}O) NMR spectroscopy to probe the oxidative degradation process in polymers at a molecular level. Due to the low natural abundance (0.037%) and a nuclear spin of I=5/2 possessing an appreciable quadrupolar moment, the use of {sup 17}O NMR in polymer investigations has been limited. By utilizing synthetically enriched oxygen gas during the accelerated aging process, both the difficulties of low natural abundance and background interference signals are eliminated. For enriched samples {sup 17}O NMR spectra now provide a unique probe since all of the observed NMR resonances are the direct result of oxidative degradation.
Date: September 1, 1997
Creator: Alam, T.M.; Click, C.A. & Assink, R.A.
Partner: UNT Libraries Government Documents Department

LDRD final report on nano-scale engineering of smart membranes

Description: A new approach to the fabrication of porous, amorphous inorganic membranes using organic pore templates was investigated. The pore templates were a new family of hybrid organic-inorganic monomers. As background for membrane work, the monomers were polymerized by sol-gel techniques to make crosslinked polymers. Molecular modeling was used to create computer simulations of the materials and provide insight into their composites, were then converted into porous silicas using low temperature oxygen plasma techniques. A select few of the monomers were copolymerized with silica monomers to form non-porous thin films on mesoporous substrates. The films were converted into porous silica thin films with thermal oxidations and the resulting membranes were tested for gas selectivities and flux.
Date: September 1, 1997
Creator: Loy, D.A.; Jamison, G.M. & Assink, R.A.
Partner: UNT Libraries Government Documents Department

An Investigation of Molecular Templating in Amorphous Silicas by Cross-Polarization NMR Spectroscopy

Description: 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. Silicon and carbon NMR experiments were performed to evaluate the efficacy of our templating approach. The {sup 29}Si NMR spectrum of the silica matrix was observed by an intermolecular cross-polarization experiment involving the {sup 1}H nuclei of TPA and the {sup 29}Si 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 xerogels, where drying stresses are greater, exhibited significantly increased interactions. Intramolecular cross-polarization experiments between the {sup 1}H and {sup 13}C nuclei of the template molecule demonstrated that much of the increased efficiency was a result of reduced rotational mobility of the TPA molecule.
Date: July 12, 1999
Creator: Assink, R.A.; Brinker, C.J.; Click, C.A. & Naik, S.J.
Partner: UNT Libraries Government Documents Department

Polymer Aging Techniques Applied to Degradation of a Polyurethane Propellant Binder

Description: The oxidative thermal aging of a crosslinked hydroxy-terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) polyurethane rubber, commonly used as the polymeric binder matrix in solid rocket propellants, was studied at temperatures of RT to 125 C. We investigate changes in tensile elongation, mechanical hardening, polymer network properties, density, O{sub 2} permeation and molecular chain dynamics using a range of techniques including solvent swelling, detailed modulus profiling and NMR relaxation measurements. Using extensive data superposition and highly sensitive oxygen consumption measurements, we critically evaluate the Arrhenius methodology, which normally assumes a linear extrapolation of high temperature aging data. Significant curvature in the Arrhenius diagram of these oxidation rates was observed similar to previous results found for other rubber materials. Preliminary gel/network properties suggest that crosslinking is the dominant process at higher temperatures. We also assess the importance of other constituents such as ammonium perchlorate or aluminum powder in the propellant formulation.
Date: July 27, 1999
Creator: Assink, R.A.; Celina, M.; Graham, A.C. & Minier, L.M.
Partner: UNT Libraries Government Documents Department

Cross-condensation reactions in an organically modified silica sol-gel

Description: High resolution {sup 29}Si NMR has been used to study the extent of cross condensation taking place in a hybrid organic/inorganic sol-gel system. Tetraethoxysilane (TEOS) and methltriethoxysilane (MTEOS) sol-gels were chosen for this purpose. The sols were prepared by acid catalyzed hydrolysis of TEOS and MTEOS with a H{sub 2}O/Si ratio of 0.3. {sup 29}Si NMR shows signals due to both self-condensation and cross-condensation between TEOS and MTEOS. Resonance assignments were made by comparing the positions and intensities of peaks in the spectra of single and multicomponent systems. It was found that, within experimental error, the self- and cross-condensation rates are equal and that extensive molecular level mixing takes place during the early stages of the reaction.
Date: December 31, 1993
Creator: Prabakar, S.; Raman, N. K.; Assink, R. A. & Brinker, C. J.
Partner: UNT Libraries Government Documents Department

Spinnability of silica sols: The role of alkoxy group exchange

Description: The exchange and spinnability of several systems with the general form Si(OR){sub 4} (where R = CH{sub 3}, C{sub 2}H{sub 5}) in ethanol, propanol and butanol were investigated. We have followed the alkoxy group exchange, hydrolysis and condensation reactions, and Q distributions of these systems using {sup 29}Si and {sup 17}O NMR. Observed differences in spinnability of the various sol-gel systems are attributed to the effect of the bulkiness of the alkoxy group on its reactivity.
Date: December 31, 1993
Creator: Prabakar, S.; Assink, R. A. & Irwin, A. D.
Partner: UNT Libraries Government Documents Department

The effect of O{sub 2} intercalation on the rotational dynamics and the ordering transition of C{sub 60}

Description: We have used {sup 13}C magic-angle spinning (MAS) nuclear magnetic resonance (NMR) to characterize the structure and rotational dynamics of C{sub 60} containing oxygen molecules located in the interstitial sites of the fcc lattice. Under normal conditions, a narrow peak at 143.7 ppm is observed for C{sub 60}. When exposed to oxygen at moderate pressures, several additional resonances appear in the {sup 13}C MAS NMR spectrum. These secondary resonances are shifted downfield from the main peak at 143.7 ppm and are due to the Fermi-contact interaction of the paramagnetic oxygen molecules with the {sup 13}C nuclear spins. The presence of oxygen depresses the orientational ordering transition by ca. 20 K as observed by DSC. The spin-lattice relaxation time (T{sub 1}) of each secondary peak shows a minimum near the ordering transition, indicating that this transition is not dependent on the number of oxygen molecules surrounding an individual C{sub 60} molecule. The T{sub 1}, due to paramagnetic relaxation, normalized by the number of surrounding oxygen molecules, is constant. This observation demonstrates that within a given sample, the dynamics of C{sub 60} molecules are independent of the number of surrounding oxygen molecules.
Date: January 1, 1995
Creator: Myers, S. A.; Assink, R. A.; Schirber, J. E. & Loy, D. A.
Partner: UNT Libraries Government Documents Department

Solar photocatalytic conversion of CO{sub 2} to methanol

Description: This report summarizes the three-year LDRD program directed at developing catalysts based on metalloporphyrins to reduce carbon dioxide. Ultimately it was envisioned that such catalysts could be made part of a solar-driven photoredox cycle by coupling metalloporphyrins with semiconductor systems. Such a system would provide the energy required for CO{sub 2} reduction to methanol, which is an uphill 6-electron reduction. Molecular modeling and design capabilities were used to engineer metalloporphyrin catalysts for converting CO{sub 2} to CO and higher carbon reduction products like formaldehyde, formate, and methanol. Gas-diffusion electrochemical cells were developed to carry out these reactions. A tin-porphyrin/alumina photocatalyst system was partially developed to couple solar energy to this reduction process.
Date: February 1, 1997
Creator: Ryba, G.; Shelnutt, J.; Prairie, M.R. & Assink, R.A.
Partner: UNT Libraries Government Documents Department

{sup 17}O NMR investigations of oxidative degradation in polymers

Description: We have initiated studies using both solution and solid state magic angle spinning {sup 17}O NMR for a series of oxidatively aged polymers. This short note reports the solution {sup 17}O NMR for oxidatively degraded polypropylene, ethylene-propylene-diene, polyisoprene, and nitrile rubber. Enriched O{sub 2} is used during the accelerated aging. 3 figs, 7 refs.
Date: December 31, 1996
Creator: Alam, T.M.; Celina, M.; Assink, R.A.; Gillen, K.T. & Clough, R.L.
Partner: UNT Libraries Government Documents Department

A Silicon, Carbon and Deuterium NMR Investigation of Molecular Templating in Amorphous Silicas

Description: 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. {sup 29}Si and {sup 2}H NMR experiments were performed to evaluate the efficacy of our templating approach. The {sup 29}Si NMR spectrum of the silica matrix was observed by an intermolecular cross-polarization experiment between the {sup 1}H nuclei of TPA and the {sup 29}Si 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. Normally prepared xerogel materials exhibited only weak interactions between the two sets of nuclei. Drying under reduced pressure, where solvation stresses are maximized, resulted in significantly increased interactions. Analogous materials were prepared using fully deuterated TPA. The {sup 2}H 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 specimens dried under reduced pressure, consistent with improved templating of amorphous silica by TPA.
Date: April 8, 1999
Creator: Alam, T.M,; Assink, R.A.; Brinker, C.J.; Click, C.A. & Naik, S.J.
Partner: UNT Libraries Government Documents Department

LDRD final report on gas separation by fullerene membranes

Description: This LDRD (Laboratory Directed Research and Development) project was funded for two years beginning in October 1992 (FY93) and was designed as a multidisciplinary approach to determining the structural and physical properties of C{sub 60} intercalated with various gases. The purpose of the study was to evaluate the relative permeation and diffusion of various gases with an ultimate goal of finding an effective filter for gas separations. A variety of probes including NMR, X-ray and neutron diffraction; IR spectroscopy, thermogravimetric analysis and mass spectroscopy were employed on C{sub 60} impregnated with a number of gases including O{sub 2}, N{sub 2}, Ar, Ne, H{sub 2}, NO and CH{sub 4}. In order to increase the absorption and decrease the effective time constraints for bulk samples, these gases were intercalated into the C{sub 60} using pressures to several kbar. The results of these measurements which were quite encouraging for separation of O{sub 2} and N{sub 2} and for H{sub 2} from N{sub 2} led to 17 manuscripts which have been published in peer reviewed journals. The abstracts of these manuscripts are shown below along with a complete citation to the full text.
Date: July 1, 1996
Creator: Schirber, J.E.; Assink, R.A.; Morosin, B.; Loy, D.A. & Carlson, G.A.
Partner: UNT Libraries Government Documents Department

Thermal Degradation Studies of A Polyurethane Propellant Binder

Description: The thermal oxidative aging of a crosslinked hydroxy-terminated polybutadiene (HTPB)/isophorone diisocyanate (IPDI) based polyurethane rubber, used as a polymeric binder in solid propellant grain, was investigated at temperatures from 25 C to 125 C. The changes in tensile elongation, polymer network properties and chain dynamics, mechanical hardening and density were determined with a range of techniques including modulus profiling, solvent swelling, NMR relaxation and O{sub 2} permeability measurements. We critically evaluated the Arrhenius methodology that is commonly used with a linear extrapolation of high temperature aging data using extensive data superposition and highly sensitive oxygen consumption experiments. The effects of other constituents in the propellant formulation on aging were also investigated. We conclude that crosslinking is the dominant process at higher temperatures and that the degradation involves only limited hardening in the bulk of the material. Significant curvature in the Arrhenius diagram of the oxidation rates was observed. This is similar to results for other rubber materials.
Date: June 12, 1999
Creator: Assink, R.A.; Celina, M.; Gillen, K.T.; Graham, A.C. & Minier, L.M.
Partner: UNT Libraries Government Documents Department

Comparison of bridged polysilsesquioxane xerogels prepared from methoxy- and ethoxy-silyl monomers

Description: Hydrocarbon-bridged polysilsesquioxanes are prepared by the sol-gel polymerization of monomers with more than one trialkoxysilyl group attached directly to the bridging group by Si-C bonds. While the effects of varying the identity of the bridging group (length, rigidity, etc.), monomer concentration, and type of catalyst have been studied, the effect of different alkoxy ligands on the silicon atoms has not been investigated. For this study, 1, 6-- bis(triethoxysilyl)hexane 1 and 1, 6-bis(trimethoxysilyl)hexane 2 were polymerized under acidic and basic conditions in ethanol and methanol, respectively, and in tetrahydrofuran (THF). The resulting gels were processed to afford xerogels that were characterized by SEM, solid state {sup 13}C and {sup 29}Si Cross Polarization Magic Angle Spinning (CP MAS) NMR spectroscopy, and nitrogen sorption porosimetry.
Date: December 31, 1994
Creator: Loy, D. A.; Baugher, B.; Assink, R. A.; Prabakar, S. & Shea, K. J.
Partner: UNT Libraries Government Documents Department

Porosity in hexylene-bridged polysilsesquioxanes: Effects of monomer concentration

Description: Hexylene-bridged polysilsesquioxanes can be prepared as mesoporous or non-porous xerogels simply by switching from basic to acidic polymerization conditions. In this study, we looked at the effect of monomer concentration on porosity of hexylene-bridged xerogels prepared under acidic and basic conditions. 1, 6-Hexylene-bridged polysilsesquioxanes were prepared by sol-gel polymerizations of 1, 6-bis(triethoxysilyl)hexane 1 with concentrations between 0. 1 to 1.2 M in ethanol. Gelation times ranged from seconds for 1.2 M concentration to months for 0.2 M. The gels were processed into xerogels by an aqueous work-up and the dry gels characterized by scanning electron microscopy (SEM), solid state {sup 13}C and {sup 29}Si CP MAS NMR spectroscopy, and gas sorption porosimetry.
Date: December 31, 1994
Creator: Baugher, B.; Loy, D. A.; Assink, R. A.; Prabakar, S.; Shea, K. J. & Oviatt, H.
Partner: UNT Libraries Government Documents Department

Intramolecular condensation reactions of {alpha}, {omega}- bis(triethoxy-silyl)alkanes. Formation of cyclic disilsesquioxanes

Description: 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 withe 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 possibility 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.
Date: August 1, 1996
Creator: Loy, D.A.; Carpenter, J.P.; Myers, S.A.; Assink, R.A.; Small, J.H.; Greaves, J. et al.
Partner: UNT Libraries Government Documents Department

Dialkylenecarbonate-Bridged Polysilsesquioxanes. Hybrid Organic Sol-Gels with a Thermally Labile Bridging Group

Description: 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, volubility, 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.
Date: April 21, 1999
Creator: Loy, D.A.; Beach, J.V.; Baugher, B.M.; Assink, R.A.; Shea, K.J.; Tran, J. et al.
Partner: UNT Libraries Government Documents Department

Preparation and characterization of phenyl-, benzyl-, and phenethyl-substituted polysilsesquioxanes

Description: Polysilsesquioxanes are a class of siloxane polymers commonly prepared by the hydrolysis and condensation of trialkoxysilanes or trichlorosilanes. From a trifunctional monomer one would expect the organically-modified polymers to be highly crosslinked and insoluble resins. However, while some silsesquioxane monomers with R = H, CH{sub 3}, or vinyl do form crosslinked polymers capable of forming gels, the majority react to form soluble oligosilsesquioxanes, including discrete polyhedral oligomers, and polymers. Because of their solubility, ladder structures have been proposed. However, viscosity studies by Frye indicate that the polyphenylsilsesquioxane is more likely best represented by a polymer rich in both cyclic structures and branches, but without any regular stereochemistry. In this study, the authors have examined the hydrolysis and condensation polymerizations of phenyltrialkoxysilane, benzyltrialkoxysilane, and 2-phenethyltrialkoxysilane monomers under both acidic and basic conditions. The resulting phenyl, benzyl and phenethyl-substituted polysilsesquioxanes were characterized by {sup 1}H, {sup 13}C, {sup 29}Si NMR, gel permeation chromatography, and differential scanning calorimetry. The effects of the organic substituent (phenyl, benzyl, phenethyl), alkoxide group (OMe, OEt), catalyst (HCl, NaOH), monomer concentration, and polymer processing on polymer molecular weight and glass transition temperature were determined.
Date: September 1, 1998
Creator: Schneider, D.A.; Loy, D.A.; Baugher, B.M.; Wheeler, D.R.; Assink, R.A.; Alam, T.M. et al.
Partner: UNT Libraries Government Documents Department