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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

I.Surface modification of poly(tetrafluoroethylene-co-hexafluoropropylene). II. Surface-initiated graft polymerization. III. Surface chemistry of fibrillar carbon

Bening, Robert Charles 01 January 1990 (has links)
Part I of this dissertation deals with the surface modification of poly(tetrafluoroethylene-co-hexafluoro-propylene) (FEP). The reduction of FEP using sodium naphthalide was studied with regard to the kinetics of reaction and the product structure. The thickness of the resulting modified surface layer could be controlled, using reaction time and temperature, in the ranges of 45-90 and 250-800 A. The air-sensitive reduction product contained carbon-carbon double and triple bonds, aliphatic C-H bonds, alcohols, carbonyls and very little fluorine. Hydroboration/oxidation introduced hydroxyl groups in high yield to the surface. The alcohols exhibited low reactivity in esterification reactions in the absence acylation catalysts. Treatment of this surface with ethylene oxide in the presence of LDA rendered a more reactive, primary alcohol-containing, surface. Reaction of the hydroxyl surface produced by hydroboration and oxidation with 1,4-toluene diisocyanate or isophorone diisocyanate resulted in surface-bound isocyanate groups. The reactivity of these surfaces towards nucleophiles was investigated. Part II deals with graft polymerization from surface-confined initiator species. Halogenated surfaces were prepared by treating reduced FEP with chlorine or bromine. Treatment of these surfaces with silver trifluoromethane-sulfonate in the presence of tetrahydrofuran (THF) resulted in the polymerization of THF from the surface. Initiation at temperatures less than $-$10$\sp\circ$C, followed by polymerization at $-$10$\sp\circ$C, resulted in a relatively thick, homogeneous overlayer of the graft polymer. Neopentyl and n-propyl alcohol groups were introduced to the surface of poly(chlorotrifluoroethylene) (PCTFE) by reaction with the appropriate protected alcohol-containing lithium reagent. The corresponding tosylate surfaces were prepared and the reaction of these surfaces with 2-methyloxazoline was studied. Acrylamide monomers were polymerized from hydroxyl surfaces derived from FEP using ceric ion redox initiation. The introduction of trimethylsilyl ketene acetal groups to polymer surfaces was also investigated. Part III deals with the surface chemistry of fibrillar carbon. Oxidation and reactions with carbenes were studied as a means of introducing functional groups to the surface. X-ray photoelectron spectroscopy was used to characterize the products; chemical derivatization was used to determine the functional group composition of the oxidized surface.
42

Syntheses and characterizations of wholly aromatic thermotropic polyesters

Bhowmik, Pradip Kumar 01 January 1990 (has links)
Thermotropic polyesters are a new class of high strength materials of significant commercial importance because of their ease of melt processing and superior properties. Several series of homopolyesters and copolyesters containing 3,3,3$\sp\prime$,5$\sp\prime$-tetrakis(sec-butyl)-4,4$\sp\prime$-biphenol, 3,3$\sp\prime$-bis(tert-butyl)-4,4$\sp\prime$-biphenol, 3-phenyl-4,4$\sp\prime$-biphenol, 3,3$\sp\prime$-bis(phenyl)-4,4$\sp\prime$-biphenol and 1,1$\sp\prime$-binaphthyl-4,4$\sp\prime$-diol were synthesized by the melt polycondensation method and characterized for their thermotropic behavior by conventional techniques. Many of these aromatic polyesters exhibited an anisotropic melt with either relatively low melting transitions or flow temperatures well below 300$\sp\circ$C, which is much lower than the thermal transitions of currently available thermotropic polyesters. Another aspect of this research program was concerned with the application of WAXD techniques to study the effect of molecular packing in the solid state of these wholly aromatic polyesters for three different series of polymers, which contained either symmetrically or unsymmetrically substituted biphenol residues in their mesogenic groups. The unsymmetrically substituted polymers showed considerably reduced crystalline order or perfection as expected, compared to the symmetrically substituted polymers which had very high degree of crystalline order or perfection. Copolymerization of both types of monomers reduced the degree of crystallization order or perfection and the melting or flow temperatures of the resulting thermotropic polyesters, as expected.
43

pH-dependent structural reorganization of phosphatidylcholine vesicle membranes by copolymers of 2-ethylacrylic acid and methacrylic acid

You, Hong 01 January 1991 (has links)
Copolymers of 2-ethylacrylic acid (EAA) and methacrylic acid (MAA) were prepared in bulk and in N,N-dimethylformamide (DMF). Best-fit terminal model reactivity ratios were determined by a non-linear least squares technique to be r$\sb{\rm MAA}$ = 1.14 and r$\sb{\rm EAA}$ = 0.23 in bulk, and r$\sb{\rm MAA}$ = 1.91 and r$\sb{\rm EAA}$ = 0.09 in 50% DMF solution, respectively. Examination of $\sp{13}$C NMR spectra provided convincing evidence for the formation of statistical copolymers. The pH-dependent structural reorganization of dipalmitoylphosphatidylcholine vesicle membranes could be effected in aqueous phosphate buffer solutions of EAA-MAA copolymers. The reorganization process is sensitive to the composition of the copolymer. Decreasing the 2-ethylacrylic acid content in copolymer shifted the 'critical' pH to lower values. Copolymers of 2-ethylacrylic acid content equal to or less than 40 mole % showed complicated aggregation in the interaction with dipalmitoyl phophatidylcholine vesicle membranes. Results from potentiometric titrations suggested that the shifts in the critical pH in the structural reorganization of DPPC vesicle membranes should be attributed to the different hydrophobic interactions of polymers. Photosensitive 3,3$\sp\prime$-dicarboxydiphenyliodonium bisulfate and hexafluorophosphate, which produced the strong acids (H$\sb2$SO$\sb4$, HPF$\sb6$) upon irradiation at 254 nm were prepared. Using these iodonium salts as proton sources, the structural reorganizations of phosphatidylcholine vesicle membranes by poly(2-ethylacrylic aicd) were demonstrated by optical density measurement and by monitoring the efflux of the calcein in entrapped vesicles. Copolymers of EAA and MAA were employed in specific enhancement of cytotoxicity of immunotoxins. It was found that the copolymer of 49 mole % 2-ethylacrylic acid content is not toxic to HeLa cells and potentiates the action of 5E7-gelonin immunotoxin. To improve the potentiating effect the copolymer was modified to have 0.9 and 1.6 mole % disulfide linkage in the side chain for attachment to the 5E7-gelonin molecule.
44

Stereochemical aspects of Ziegler-Natta catalysts

Vizzini, James Charles 01 January 1991 (has links)
The advent of MgCl$\sb2$ supported Ti catalysts and more recently the chiral ansa-bridged metallocene homogeneous systems has sparked interest concerning the stereochemical nature of these two classes of Ziegler-Natta catalysts. A classical method of separating chiral sites in heterogeneous systems is by the introduction of an optically active third component and studying the physical properties of the fractionated polymer obtained from the polymerization of racemic monomer. In the homogeneous case an optically pure catalyst may be obtained and as described above, information may be gleaned from racemic monomer polymerization. The system MgCl$\sb2\cdot$3ROH/phthalic anhydride/TiCl$\sb 4$/dialkylphthalate//triethylaluminum/phenyltriethoxysilane was studied. The effect of changing the alkyl group of the ester was that the bulkier alkyl resulted in poorer stereospecific yields of the system. Magic angle spinning cross-polarization $\sp{13}$C NMR revealed that the ester was rigidly bound to the support and that the above system had clearly more than one type of complexation of the ester unlike an earlier supported system indicating more diverse defect structures on the surface. The system was modified with (R,S)- and (S)-2-methyl-1-butanol accompanied by the respective phthalate esters. Activities of 3- and 4-branched $\alpha$-olefins were more depressed than that of earlier supported systems. Active site counting in the polymerization of 4-methyl-1-pentene with a supported system revealed that fewer active sites are available for this monomer than for propylene. Polymerizations of racemic monomer were stereoelective but for the 3-branched monomer the polymer produced was more stereoirregular than those from earlier supported systems. Polymerization of racemic 4-methyl-1-hexene with the homogeneous (S)-ethylenebis($\eta\sp 5$-tetrahydroindenyl)zirconiumbis(O-acetyl-(R)-mandalate)/methylaluminumoxane system produced more optically pure and stereoregular polymer than the heterogeneous systems. The existence of fractions in the polymer of opposite optical rotation suggests that at least two stereochemical environments exist during the course of the polymerization, disputing earlier beliefs that this system is stereochemically rigid. Also, it was found that the type of solvent used in the polymerization could affect the stereochemical distribution of the system.
45

Synthesis and interfacial activity of copolymers with specific functionality and architecture

Viviano, Katrina Rose 01 January 1994 (has links)
This thesis has two main objectives (1) synthesizing block copolymers containing specifically functionalized segments in well-defined locations and densities and (2) studying the interfacial activity of these copolymers as a function of composition. Interfacial activity is assessed through adsorption at the solution/solid interface and the polymer/air interfaces. The approach for preparing these functionalized diblock copolymers involved anionically copolymerizing an unfunctionalized monomer with a functionalized monomer. The functionalized copolymer, poly (styrene-co-(p-hydroxystyrene)), because of the acidity of the phenolic group protective group chemistry was required. Therefore the protected monomer, 4-(tert-butyldimethylsilyl)oxystyrene, was synthesized. Poly (styrene-co-(p-hydroxystyrene)) of known composition and structure was synthesized through the copolymerization of styrene and 4-TBDMSoxystyrene. Subsequent desilylation of the tert-butyldimethylsilyl ether generated the phenol functionality. This deprotection was quantitative, generating poly (styrene-co-(p-hydroxystyrene)). The protected and the deprotected copolymers were used to characterize the copolymer's composition. The adsorption behavior of poly (styrene-co-(p-hydroxystyrene)) was studied at the solution/solid interface. The amount of polymer adsorbed was studied as a function of copolymer composition. Using UV depletion, adsorption was studied from THF to alumina generating for each polymer studied adsorption isotherms. At each molecular weight, polystyrene served as a control and the amount of copolymer adsorbed was found to be a function of composition. The adsorption results agreed qualitatively with theoretically predicted behavior. The reactivity of the phenol functionality was used as a reactive handle to incorporate surface-active groups (perfluoroalkyl groups) at defined locations and densities along the copolymer chain, generating a surface-active polymer (SAP) of known composition. The adsorption behavior of these SAPs was studied from a 10K polystyrene matrix. Adsorption was studied as a function of SAP concentration and composition. Heat treated 10K polystyrene films served as a control. At all SAP compositions studied there was an enrichment of the surface region with SAP. The perfluoroalkyl groups preferentially adsorbed at the polymer/air interface as indicated by XPS and contact angle data. The amount of SAP adsorbed was found to be a function of composition. This adsorption data provides experimental evidence that copolymer composition influences adsorption behavior and ultimately surface composition.
46

The versatile chemistry of azidoalkyl enol ethers and their equivalents

Liddon, John Timothy Ruskin January 2015 (has links)
This thesis describes the synthesis and intramolecular cycloaddition products of azides tethered to olefins bearing a heteroatom in an attempt to access a proposed triazolium intermediate 77. Chapter 1 covers the synthesis and reactivity of simple di- and trisubstituted azidoalkyl enol ethers. These substrates were found to provide isolable 1,2,3-triazoline products, but displayed a propensity to aromatise to 1,2,3-triazoles upon ionisation. Difficulties in synthesising fully-substituted azidoalkyl enol ethers have precluded a detailed study in this project, though a bias towards α-alkoxy imine formation was suggested. Chapter 2 covers the chemistry of azidoalkyl vinyl bromides. Simple vinyl bromide substrates were found to yield 1-azadienes upon thermolysis, presumably via the dehydrobromination of an α-bromo imine intermediate in situ. In Chapter 3, a brief diversity-oriented synthesis (DOS) campaign was undertaken to demonstrate the potent reactivity of 1-azadiene substrates. 1-Azadienes were found to be versatile intermediates, and a small DOS library was built by exploiting several key reactivity modes. In Chapter 4, two miscellaneous routes towards the desired triazolium intermediate are discussed, and finally an Appendix chapter deals with an attempted total synthesis of salinosporamide C.
47

Supramolecular devices as selective receptors

Roshandel, Sahar 01 October 2015 (has links)
<p>We have found that calixarenes are good receptors of choline (trimethylammonium group) and they have strong affinity to form host-guest complexes with a variety of molecules carrying this moiety. Furthermore, the ability of lower rim carboxylic acid calix[n]arenes and upper rim phosphonic acid functionalized calix[4]arene to transport choline-conjugated drugs through a liquid membrane was discovered. The results demonstrate that these systems are highly efficient toward transporting choline-conjugated targets, as well as neurotransmitters that possess ionizable amine termini. The breadth of compounds that are transported is significant, facing limitations only when the payloads become extremely lipophilic. These developments reveal new approaches towards attempting synthetic receptor mediated selective small molecule transport in vesicular and cellular systems.
48

Vapor phase combustion

Karsten, Andrew, January 1922 (has links)
Thesis (Ph. D.)--Ohio state University, 1922. / Autobiography.
49

Vapor phase combustion,

Karsten, Andrew, January 1922 (has links)
Thesis (Ph. D.)--Ohio state university, 1922. / Autobiography.
50

Structure and excitation energy in retinals and retinal proteins

Ren, Lei. Birge, Robert R. January 2004 (has links)
Thesis (Ph. D.)--Syracuse University, 2004. / "Publication number AAT 3132711."

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