Tübingen, Univ., Diss., 2003.

Inaug.-diss.--Strassburg.

No description available.

Building upon existing synthetic methods, we have optimized the synthesis of Thiele’s methyl ester to an efficient and scalable methodology. As part of a study of chemo- and regioselective transformations within the Thiele’s ester scaffold, we designed and synthesized a new suite of molecular scaffolds incorporating a broad range (from 123° to 176°) of cleft angles. In addition to this, we compared two competing conceptual models for their ability to rationalize the selective formation of Thiele’s ester and two minor regioisomers which arise during the formation of the target product. We found that radical stabilization arguments (based on Deslongchamps’ seminal work) outperformed the classic frontier molecular orbital theory model in predicting the regioselectivity of Thiele’s ester dimerization. When this method was combined with simple steric arguments, we arrived at a general algorithm to rationalize Thiele type dimerization, including all the known homo- and heterodimerizations in the literature as well as a novel phosphine oxide-containing Thiele acid analogue discovered as part of this thesis work. In order to stimulate the use of Thiele’s ester chemistry in a diverse range of applications, we took advantage of our Thiele’s ester methodology to achieve a mono ester-substituted dicyclopentadiene (colloquially referred to as a “half” Thiele’s ester), and used this as the precursor of a novel functionalized polydicyclopentadiene (fPDCPD) ROMP polymer. The resulting fPDCPD has the highest glass-transition temperature reported for any polydicyclopentadiene material and allows for the facile manipulation of the surface chemistry through alteration of the embedded functional group. A long-term goal in the Wulff lab is to use Thiele’s ester as a scaffold for the generation of conformationally restricted (“peramivir-like”) neuraminidase inhibitors. Setting the groundwork for this, we explored the selectivity of various peramivir derivatives toward group-1 vs. group-2 neuraminidase enzymes. To this end, we coupled a wide range of alkyl chains and aromatic rings with different length and size parameters onto the primary amine of peramivir. We found that our de-guanidinylated peramivir analogues showed a rare target selectivity against group-2 neuraminidases instead of group-1 neuraminidases, which might due to the ring geometry of peramivir as well as the reduced electrostatic interaction between the amino group from our analogues and the Asp147-His150 residues from the enzyme. This suggested that it is possible for group-2 neuraminidases to have a more open 150-cavity state than group-1 neuraminidases. Additionally, the respectable IC50 values for these compounds, together with their significantly reduced polarity (relative to peramivir itself) may prove advantageous from a bioavailability standpoint. / Graduate / 2019-04-30

One of the major classes of polymer matrix resins under consideration for structural composite applications in the infrastructure and construction industries is the dimethacrylate matrix resin. An investigation of the relationships between the chemical structures and properties of these dimethacrylate/styrene networks has been conducted. Oligomer number average molecular weights of the polyhydroxyether ranging from 700 to 1200g/mole were studied with systematically varied styrene concentrations to assess the effects of crosslink density and chemical composition on glass transition temperatures, toughness, tensile properties and matrix strain. Network densities have been estimated from measurements of the rubbery moduli at Tg + 40°C. Within this rather small range in vinyl ester molecular weight, toughness of the resultant networks improved tremendously as the vinyl ester oligomer Mn was increased from 700g/mole to 1200g/mole due to improvements in the resistance to crack propagation. As styrene concentration was increased along all series' of materials, brittleness increased even though the molecular weight between crosslinks increased. This was attributed to the inherent relative brittleness of the polystyrene chemical structure relative to the polyhydroxyether component. This may also be related to the reactivity ratios dictating styrene and vinyl ester sequence length and warrants further investigation. As expected, the volume contraction upon cure also decreased significantly as styrene was decreased, and thus residual cure stresses may be reduced in fiber-reinforced composites. Vickers microhardness values decreased for each of the series when molecular weight increased and styrene content decreased. Two different cure procedures were compared to assess the effects of conversion on the physical and mechanical properties. All mechanical properties investigated (i.e. fracture toughness, tensile strength, and microhardness) were dependent on the cure procedure. Materials cured at 140°C were harder, more brittle, had lower elongations and higher rubbery moduli than those cured at 25°C followed by a 93°C postcure. A maximum in the degree of conversion occurred with increasing polymerization temperature and can be explained by the competition between the chemical reaction and molecular mobility. The overall shrinkage per moles of vinyl groups converted was the same when the materials were cured at 25°C or 140°C. However, in the room temperature cured samples, there was essentially no further densification of the network during postcure, regardless of the postcure temperature. A mono-methacrylate analogue of the dimethacrylate terminated poly(hydroxyether) oligomer was synthesized and copolymerized with styrene to study the effects of chain transfer during elevated temperature reactions. / Ph. D.

Thesis advisor: James P. Morken / The Suzuki-Miyaura cross-coupling reaction is a common strategy for the formation of a new carbon-carbon bond in organic synthesis. However, intramolecular coupling of allylboron ester and aryl electrophiles has never been reported. Herein, Pd-catalyzed intramolecular cross-coupling of allylboronic pinacol ester and vinyl or aryl bromides is presented. Pt-catalyzed 1,2-diboration of 1,3-dienes give α-chiral bis-allylboronic esters, which can undergo diastereoselective additions to carbonyl electrophiles tethered to vinyl or aryl halides to generate a new allylboronic ester moiety. Under Suzuki coupling conditions, the allylboronic esters moiety and the vinyl bromides in the allylation products can cross-couple in an intramolecular fashion to afford highly substituted four-, five-, and six-membered rings with excellent yields and moderate diastereoselectivity. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

We report a method of increasing fracture toughness (KIc) and strain energy release rate (GIc) of vinyl-ester (VE) matrix by adopting a hybrid (dual) reinforcement strategy. The idea of using this strategy was to trigger intrinsic polymer-nanoparticle interaction such as carbon nanotube (CNT) pull-out and interface sliding to enhance energy absorption during fracture. Additionally, we included a second reinforcement, graphene nanoplatelets (GNP), to promote crack-deflection, crack bridging and cross-linking density. Both reinforcements were dispersed into the polymer in three states: non-functionalized (nf>); functionalized with COOH (f>); surface-treated with Triton X-100 (TX100). We embarked on numerous experiments with many combinations of these variables. We measured KIc and GIc using ASTM D5045-14. We conducted an exhaustive iterative investigation with three systems (f>CNT-VE; f>GNP-VE; f>CNT-f>GNP-VE) to determine the best weight-percentage for the nanocomposite system that produced the highest KIc and GIc values when compared to neat-VE. We found that 0.5wt% f>CNT with 0.25wt% f>GNP in the VE matrix resulted in the highest fracture toughness values and was termed the optimized hybrid nanocomposites (OHN) system. Subsequently, we explored further increasing the KIc and GIc of OHN through altering the nanoparticle surface characteristics, which led to four OHN groups: f>CNT-f>GNP-VE; f>CNT-f>GNP-TX100-VE; nf>CNT-nf>GNP-TX100-VE; nf>CNT-nf>GNP-VE. We discovered that the OHN group with non-functionalized nanofillers that were TX100 surface treated (0.5wt%nf>CNT-0.25wt%nf>GNP-TX100-VE) generated the greatest improvements in KIc and GIc. Ultimately, we observed that the KIc of neat-VE increased by 65%, from 1.14 to 1.88 MPa*(m½). The improvement in GIc was even greater with an increase of 166%, from 370 to 985 J/(m2). Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) studies showed a minor shift in glass transition temperature (Tg) by up to 8°C when comparing neat-VE specimens to OHN specimens. A similar increase in maximum thermal decomposition temperature (Tp) of up to 8°C was observed through thermogravimetric analysis (TGA) and derivative TGA (DTG). Scanning electron microscope (SEM) studies revealed that the source of improvements in fracture toughness and thermal properties was primarily the three-dimensional hybrid nanostructures (3DHN) that formed by binding CNT and GNP together, which caused an increase in nanoparticle surface area and inhibited agglomerations. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Thesis (doctoral)--Christian-Albrechts-Universität zu Kiel, 2002.

Tomorrow’s lightweight, high-performance composite systems will be made of structures built with materials that have unprecedented intrinsic properties for performing a wide range of functions, such as EMI shielding, thermal management, flame resistance, lightning strike protection, acoustic damping, and health-monitoring. Current structures require parasitic components, e.g., metal strips, copper wire meshes, strain gauges, and heat sinks to provide these functions. By eliminating parasitic components, future high-performance multifunctional systems can achieve the intended objectives, while maintaining optimum weight, reliability, cost, and fuel efficiency. With the continuing growth of polymer composites in industries, such as aerospace, automotive, and wind energy, research and development on lightweight, high-performance composites that possess extraordinary properties for future multifunctional systems has generated considerable interest and excitement. Recent advances in nanomaterial synthesis and functionalization have shown that tailored property combinations are possible with reduced parasitic content to achieve multifunctionality. Cyanate ester (CE), a class of high-performance thermosetting resins (high T [subscript g], >250°C), has received considerable attention due to its good mechanical properties, thermal stability, flammability properties, ease of process, and volatile-free curing process. Multiwall carbon nanotubes were selected due to their unique combination of excellent mechanical, electrical, and thermal properties. The principal objective of this work is to determine the extent to which several different processing techniques will affect the MWNT dispersion and corresponding nanocomposite properties, such as thermal, flammability, mechanical, and electrical properties. A processing-structure-property relationship, as well as performance of this class of carbon-based CE nanocomposite, will be established. Therefore, a major scientific contribution of this study will be the development and characterization of a novel, multifunctional CE nanocomposite. Different mixing instruments, such as high shear mixer, ultrasonicator, planetary centrifugal mixer, etc. were used to disperse the nanotubes in the cyanate ester resin matrix. Microstructural morphology characterizations by SEM, STEM, and TEM show that various degrees of dispersions of MWNTs were obtained by the different mixing techniques. An attempt to quantify the MWNT dispersion was made. Electrical resistivity of samples processed by both stand mixer and three-roll mill passes the ESD requirement; however, the MWNT percolation thresholds by the two techniques are different. Thermal analysis shows that the addition of the Fe³+ catalyst or the coupling agent lowers the glass transition temperature and degrades the mechanical properties (e.g., storage modulus, tangent of phase angle delta) of the CE resin. On the other hand, processing techniques only affect the mechanical properties of the resin. Thermal stability of CE is only slightly affected by different processing techniques, as well as the addition of MWNTs. Much more significantly, flammability characterization shows that the incorporation of either the Fe³+ catalyst or the coupling agent substantially increases the peak heat release rate (PHRR) relative to the neat CE resin value. / text

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