Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 296-301). Also available via the Internet.

No description available.

The interphase region at modified polymer surfaces or at polymer\ metal interfaces may be critical in determining the strength and durability in adhesive applications. Methods to investigate these regions are limited however and this research has focused on the use of infrared reflection absorption spectroscopy (IRRAS) and x-ray photoelectron spectroscopy (XPS) to investigate the molecular structure of both modified and unmodified thin films. The optical constants of polyphenylene sulfide (PPS) were determined and exact optical theory was utilized to simulate spectra for a variety of reflectance techniques. This method was also utilized to confirm the ordered state of thin spin coated PPS films. The surface modification of polystyrene, polyphenylene sulfide, and poly(arylene ether) phosphine oxides was also examined by these techniques and optical theory used to optimize experimental conditions. Results after plasma treatment indicated a very thin modified surface layer (< 10 nm) where the thickness and specific surface chemistry depended on the polymer and plasma gas used. The interaction of an epoxy resin with a surface modified PPS film showed that while most of the modified surface layer is removed after this treatment, a remaining amount can serve to cross-link a thin adsorbed epoxy film. Results for the oxygen plasma treatment of poly(arylene ether) phosphine oxides showed the formation of a surface phosphate layer that inhibited further plasma etching. The kinetics of formation and the particular chemistry involved were examined in detail. A new technique, variable temperature reflection absorption spectroscopy (VTRAS) was developed as a method to investigate the reorganization of thin PPS films on a variety of substrates. Both the crystallization and melting temperatures could be determined for quenched coatings on a variety of substrates. While degradation under vacuum was not observed on chromium and aluminum surfaces, PPS films on copper surfaces showed a loss in crystallizability, and did not return to the original ordered state after exposure to temperatures near 300°C. Loss of cuprous oxide was also observed, and chain scission mechanisms were postulated. Additional measurements on thin sputtered cuprous oxide films showed less degradation for the same temperature treatments, emphasizing the role of the underlying metal in the degradation process. Spin coated films of polyetherimide were shown to be oriented after spin coating, and the relaxation to a more random state could also be observed by the VTRAS technique. Degradation of PPS films in air was examined and the diffusion of copper species into the bulk of the film with the formation of copper carboxylates was observed. The use of the VTRAS technique in air also was useful in determining the temperature needed for the onset of degradation. Bonded PPS/copper laminates were investigated and results showed that the particular surface chemistry was crucial in determining the peel strength observed. After a simple thermal! oxidation pretreatment for copper foil, an increase in the peel strength of almost one order of magnitude was observed over non-oxidized foils. Chemical oxidation with alkaline persulfate solutions resulted in a needle-like surface oxide morphology, and bond strengths were also increased by this pretreatment method. Failure surface analysis and model interaction studies with PPS tetramer showed that the formation of excess cuprous sulfide at the interface was the most probable cause of poor adhesion in these systems. Foil pretreatment by thermal oxidation gave the highest peel strength, and also exhibited the lowest amount of interfacial cuprous sulfide. / Ph. D.

No description available.

No description available.

In the effort to improve oil production riser performance, new materials are being studied. In the present case, a Polymer Matrix Composite (PMC) is being considered as a replacement for carbon steel in flexible risers manufactured by Wellstream Inc., Panama City, Florida. The Materials Response Group (MRG) at Virginia Tech had the primary responsibility to develop the models for long-term behavior, especially remaining strength and life. The MRG is also responsible for the characterization of the material system with a focus on the effects of time, temperature, and environmental exposure. The present work is part of this effort. The motivation to use a composite material in a non-bonded flexible riser for use in the offshore oil industry is put forth. The requirements for such a material are detailed. Strength analysis and modeling methods are presented with experimental data. The effect of matrix crystallinity on composite mechanical properties is shown. A new method for investigating matrix behavior at elevated temperatures developed. A remaining strength life prediction methodology is recalled and applied to the case of combined fatigue and rupture loading. / Master of Science

Fluoropolymers have useful properties including high thermal stability, chemical resistance, low dielectric constants, and both hydrophobic and oleophobic character, as compared to non-fluorinated analogues. Meanwhile, Diels-Alder polyphenylenes (DAPPs) are known for thermal stability as well as their rigid structure and glassy physical characteristics, which have led to a variety of film and membrane applications. This dissertation merges these two fields by demonstrating a novel and general synthetic approach to highly fluorinated DAPPs. These polymers are expected to retain the physical characteristics of glassy, non-fluorinated DAPPs while also incorporating the desirable attributes of fluoropolymers. The polymer synthesis described herein is based on the well-established polycondensation of bis(cyclopentadienone) (CPD) monomers and dialkynes. Our first main scientific contribution is a general method for preparing CPDs containing both a fluoroaromatic linker and variable fluoroaromatic head-groups. Our CPD synthesis uses nucleophilic aromatic substitution reactions of cyclopentadienyl anions and perfluoroarenes, as well as a new catalytic method of converting cyclopentadiene methylene (CH₂) groups into the corresponding ketones (C=O) that is the primary dissertation subject of Brian S. Hickory in our laboratory. The overall synthesis is notable for its use of inexpensive starting materials, its efficiency, and its structural versatility. Our second main contribution is the synthesis of novel highly fluorinated Diels-Alder polyphenylenes (DAPPs). Fluorinated DAPPs varied in their molecular weight, in the identity of the lateral fluoroaryl substituent (pentafluoro-phenyl or tetrafluoro-4-pyridyl), and in the structure of the aromatic dialkyne monomer. These polymers are glassy materials with high glass transition temperatures and high thermal stability. Since the polyphenylene structure is intrinsically rigid, the polymers form brittle films even at molecular weights of over 30,000 (M_w). Unlike many fluoropolymers, the fluorinated DAPPs are freely soluble in common organic solvents such as tetrahydrofuran and chloroform. An unknown side reaction competes with the polymer propagation and reduces the highest obtainable molecular weights, which limit the ability to form films. However, a stoichiometric imbalance leads to highly fluorinated polyphenylene oligomers terminated with either alkyne or CPD end groups (M_n = 9000). Because preliminary experiments had shown that the desired Diels-Alder propagation reaction was slower than expected, we also undertook a detailed model study of the reaction conditions needed for Diels-Alder reactions of fluorinated CPDs and aromatic alkynes. These experiments showed that protic polar solvents (e.g., m-cresol) and conventional heating at ca. 150 °C optimize reaction rate while minimizing side-reactions that can contribute to lower molecular weight in corresponding polymerization reactions. / Ph. D.

Neue nanoporöse Materialien mit niedrigen Dielektrizitätskonstanten werden in der Mikroelektronik dringend benötigt. Eine Methode, die Dielektrizitätskonstante eines gegebenen Materials weiter zu reduzieren, ist die Einführung von geschlossenen und luftgefüllten Poren im Nanometerbereich. Die Porosität wird durch die Verwendung eines Zweikomponentensystems bestehend aus einer stabilen Matrix und einem labilen Porenbildner eingeführt; aus diesen wird ein Blend hergestellt, und durch anschließende Zersetzung des Porenbildners entsteht ein poröses Matrixpolymer mit stabilen Aushöhlungen. Im Vordergrund dieser Arbeit stand die Synthese und Charakterisierung hochverzweigter Polyphenylene über die Diels-Alder-Reaktion von phenylierten Cyclopentadienonen mit phenylierten Alkinen zur Verwendung als Matrixmaterialien in nanoporösen Isolatorsystemen. Dabei wurde sowohl von A2- und B3-Monomeren als auch von AB2- und AB-Monomeren ausgegangen. Die hochverzweigten Polyphenylene sind vielversprechende Materialien mit hervorragenden isolierenden und chemischen Eigenschaften wie hohen thermischen Stabilitäten und guten Löslichkeiten in organischen Lösungsmitteln, was eine wichtige Voraussetzung für die Verwendung der Polymere in der Mikroelektronik darstellt. Die verschiedenen Syntheseansätze erlauben dabei eine Kontrolle über die Endgruppen und die Verzweigung. Daneben wurden thermolabile hochverzweigte Polycarbonate und Polytriazenester als Porenbildner synthetisiert und mit Silylether-Endgruppen modifiziert, wobei mit der tert-Butyldiphenylsilyl-Gruppe die besten Ergebnisse bezüglich der Mischbarkeit mit der Polyphenylenmatrix erhalten wurden. Außerdem wurden Blends in Form von dünnen Schichten aus den hochverzweigten Polyphenylenen mit den Porenbildnern im Hinblick auf die potentielle Anwendung der Materialien als nanoporöse Isolatoren charakterisiert.

Conjugated organic polymers have attracted immense interest for use in the active layer of photovoltaic cells, electroluminescent displays and diagnostic sensors. Precise control of the chemical structure of these conjugated materials is essential to achieve better device performance and certain structural aspects which have received minimal investigation include; the nature of the end groups, the precise control of the molecular weight and the formation of novel polymer topologies. Absolute control of these factors, in particular the end groups, has the potential to further tune the electro-optical properties, eliminate charge trapping and reactive sites, and facilitate block copolymer formation. The ring opening metathesis polymerisation of highly strained cyclophanediene monomers has proven to be an advantageous route to obtain soluble poly(p-phenylenevinylene)s (PPVs). In an extension of this previous work PPVs with both a pristine polymer backbone microstructure and a range of well-defined functional end groups have been prepared. These polymers exhibited excellent degrees of functionality, relatively narrow unimodal distributions and degrees of polymerisation much higher than those attainable by alternate routes. In particular the incorporation of an α-bromoester end group directly resulted in PPVs which were effective macroinitiators in the atom transfer radical polymerisation of methyl methacrylate. The diblock copolymers prepared by this route were isolated with narrow polydispersities, unimodal distributions and were free from homopolymer impurities. This method of preparing rod-b-coil diblock copolymers, where the properties of the two segments can readily be modified, provides access to materials which are of interest for both their self-assembly ability and for the development of a much required phase diagram in this area. Cyclic PPVs are of synthetic interest both for the absence of any end groups and for an infinitely long π-conjugated backbone, both of which are expected to contribute to unique electro-optical properties. The preparation of these target polymers was investigated by the ring expansion metathesis polymerisation of the cyclophanediene monomers. The formation of purely cyclic, low molecular weight PPVs was found to be highly dependent on both the reaction conditions used and the nature of the solubilising substituents. For example the preparation of purely cyclic PPVs with alkoxy side chains was unsuccessful, however the incorporation of alkyl side chains allowed for the successful isolation of the desired cyclic polymers.

Neue nanoporöse Materialien mit niedrigen Dielektrizitätskonstanten werden in der Mikroelektronik dringend benötigt. Eine Methode, die Dielektrizitätskonstante eines gegebenen Materials weiter zu reduzieren, ist die Einführung von geschlossenen und luftgefüllten Poren im Nanometerbereich. Die Porosität wird durch die Verwendung eines Zweikomponentensystems bestehend aus einer stabilen Matrix und einem labilen Porenbildner eingeführt; aus diesen wird ein Blend hergestellt, und durch anschließende Zersetzung des Porenbildners entsteht ein poröses Matrixpolymer mit stabilen Aushöhlungen. Im Vordergrund dieser Arbeit stand die Synthese und Charakterisierung hochverzweigter Polyphenylene über die Diels-Alder-Reaktion von phenylierten Cyclopentadienonen mit phenylierten Alkinen zur Verwendung als Matrixmaterialien in nanoporösen Isolatorsystemen. Dabei wurde sowohl von A2- und B3-Monomeren als auch von AB2- und AB-Monomeren ausgegangen. Die hochverzweigten Polyphenylene sind vielversprechende Materialien mit hervorragenden isolierenden und chemischen Eigenschaften wie hohen thermischen Stabilitäten und guten Löslichkeiten in organischen Lösungsmitteln, was eine wichtige Voraussetzung für die Verwendung der Polymere in der Mikroelektronik darstellt. Die verschiedenen Syntheseansätze erlauben dabei eine Kontrolle über die Endgruppen und die Verzweigung. Daneben wurden thermolabile hochverzweigte Polycarbonate und Polytriazenester als Porenbildner synthetisiert und mit Silylether-Endgruppen modifiziert, wobei mit der tert-Butyldiphenylsilyl-Gruppe die besten Ergebnisse bezüglich der Mischbarkeit mit der Polyphenylenmatrix erhalten wurden. Außerdem wurden Blends in Form von dünnen Schichten aus den hochverzweigten Polyphenylenen mit den Porenbildnern im Hinblick auf die potentielle Anwendung der Materialien als nanoporöse Isolatoren charakterisiert.