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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.
1

Hydrophilic Polymers of Poly (2-Hydroxy Ethyl Methacrylate) with Tunable Properties for Drug Release, Sequestration of Blistering Agent, Preparation of Ultra-Strong Hydrogels & Thermal Stability of Various Organic Azides

Ananthoji, Ramakanth 01 January 2012 (has links)
The design and synthesis of new finely tunable porous materials has spurred interest in developing novel uses in a variety of systems. Zeolites, inorganic materials with high thermal and mechanical stability, in particular, have been widely examined for use in applications such as catalysis, ion exchange and separation. A relatively new class of inorganic-organic hybrid materials known as metal-organic frameworks (MOFs) has recently surfaced, and many have exhibited their efficiency in potential applications such as ion exchange and drug delivery. A more recent development is the design and synthesis of a subclass of MOFs based on zeolite topologies (i.e. ZMOFs), which often exhibit traits of both zeolites and MOFs. Bio-compatible hydrogels already play an important role in drug delivery systems, but are often limited by stability issues. Thus, the addition of ZMOFs to hydrogel formulations is expected to enhance the hydrogel mechanical properties, and the ZMOF-hydrogel composites should present improved, symbiotic drug storage and release for delivery applications. Herein we present the novel composites of a hydrogel with a zeolite-like metal-organic framework, rho-ZMOF, using 2-hydroxyethyl methacrylate (HEMA), 2,3-dihydroxypropyl methacrylate (DHPMA), N-vinyl-2-pyrolidinone (VP) and ethylene glycol dimethacrylate (EGDMA), and the corresponding drug release. An ultraviolet (UV) polymerization method is employed to synthesize the hydrogels, VP 0, VP 15, VP 30, VP 45 and the ZMOF-VP 30 composite, by varying the VP content (mol%). The rho-ZMOF, VP 30, and ZMOF-VP 30 composite are all tested for the controlled release of procainamide (protonated, PH), an anti-arrhythmic drug, in phosphate buffer solution (PBS) using UV spectroscopy. Blister agents are chemical compounds that induce severe skin, eye, mucosal pain and irritation. The research focuses on sequestering a blister agent analog, thioanisole in hydrogels. HEMA polymers and copolymers of HEMA with 2,3-dihydroxyproyl methacrylate (DHPMA) and vinyl pyrrolidone (VP) were synthesized with crosslinkers of various dimensions. These were: ethylene glycol dimethacrylate (EGDMA), diethylene glycol dimethacrylate (DiEGDMA), triethylene glycol dimethacrylate (TriEGDMA), tetraethylene glycol dimethacrylate (TetEGDMA) and neopentyl glycol dimethacrylate (NPEGDMA). Equilibrium swelling was characterized gravimetrically and pore size was estimated via scanning electron microscopy (SEM). Glass transition temperatures were measured by differential scanning calorimetry (DSC). The absorption of thioanisole in methanol was characterized with via ultra-violet (UV) spectroscopy. Poly(2-hydroxyethyl methacrylate) (PHEMA) composites constructed from a paddle-wheel, a secondary building unit (SBU) for metal organic frameworks, Cu2(p-OH benzoate)4(DMSO)2*2DMSO (CPW) were also investigated for a broad analysis of dielectric spectra. The dielectric spectrum of poly(2-hydroxyethyl methacrylate) and its copolymer with Poly(2,3-dihydroxy propyl methacrylate) (PDHPMA) are already reported in the literature. This study delineates the effects on the dielectric behavior as a result of CPW addition. The dielectric permittivity and the loss factor were measured using a dielectric analyzer in the frequency range of 1 Hz to 100 k Hz and between the temperature range of -140 and 250°C. The electric modulus formalism was used to reveal the viscoelastic and conductivity relaxations present in the polymers. Significant changes were observed as CPW concentration increased from 0.1 to 0.5 wt%. It was determined through DSC that the glass transition temperature increased with the filler concentration. The secondary dielectric relaxations were also affected as it was recorded that the activation energy for the γ, Β, and conductivity relaxation increased with CPW content. AC and DC conductivity are also evaluated. The ionic conductivity data revealed that the CPW impedes the ion mobility when compared to the neat PHEMA. Organic azides have become a very vital class of chemical compounds in synthetic organic chemistry and in many more fields due to their applications. Azido compounds are considered high-energetic compounds and are studied very little due to their explosive nature. There is an urge to evaluate the thermal stability of this wide variety of compounds which have tremendous applications in synthetic as well as organic chemistry. Here in we report the thermal stability of some organic azides such as sulfonyl, phosphoryl and carbonyl azides using differential scanning calorimetry (DSC) as an evaluating tool. Initial temperature of decomposition (Ti) and temperature of maximum decomposition (Tmax) are recorded. The area under exotherm peak during decomposition is used to determine the energy of decomposition (Ed) and is compared to threshold value for hazardous/explosive compounds. The effect of substituent groups at different positions, nature of the substituent groups (electron donating or electron withdrawing) and the steric hindrance on the thermal stability of these azides is studied in detail to verify the explosive nature of these compounds.
2

Polyvinyl alcohol (PVA) adhesives reinforced by microfibrillated cellulose (MFC) – adhesive properties and reinforcement mechanisms

Wloch, Daniela January 2019 (has links)
The aim of the project was to investigate a green and sustainable replacement for boric acid in polyvinyl alcohol (PVA) adhesives for solid paperboard production. Boric acid acts as a cross-linker and tackifier in the adhesive but is classified as a harmful substance. Microfibrillated cellulose (MFC) was therefore investigated as a possible replacement for boric acid since it is produced from renewable and sustainable resources. In addition, it has hydroxyl groups available for interaction with the PVA, can be used to modulate the viscosity and can function under a variety of pH-values.  For the industrial process, there are three basic characteristics which must be met by the newly developed adhesive, which have to be the same as for the boric acid-containing reference. These three are the viscosity, the pH-value, and the dry content. Furthermore, it is important that the initial wet tack and the final adhesive strength are at least as high as the reference’s.  In this context, eight types of samples were investigated in total. Two were references, one prepared on industrial and the second on a laboratory scale according to a current industrial recipe. In the other six samples, the boric acid from the recipe was replaced by three different weight percentages of MFC of two different industrial grades. Both the dry content and the pH-value were not noticeably influenced by the addition of MFC. The viscosity however increased drastically with the increasing amount of MFC. The addition of MFC was enough to reach the three basic characteristics. In addition it was observed positive effects on a couple of other parameters that is beneficial for the glue.   A test method for evaluating the initial wet tack of the adhesive was developed. It was shown, that the tack of the adhesive containing MFC is 40 % lower than the one of the reference material. Therefore, five additives were tested in the formulation, in combination with MFC. The most promising result led to a comparable initial tack and final strength as the reference.
3

INVESTIGATIONS TOWARDS THE PREPARATION OF PHOTORESPONSIVE POLYMERS BASED ON PHOTOCLEAVABLE TELLURIUM-CONTAINING CROSS-LINKS

Gendy, Chris 10 1900 (has links)
<p>The goal of this research project is to synthesize, characterize, and examine the properties of a material that undergoes a decrease in refractive index upon exposure to light. It is anticipated that such photoresponses could elicit previously unknown nonlinear phenomena including self-trapped black beams. An appropriate material for these investigations would be a polymer cross-linked by photocleavable groups causing a Δ<em>n</em> < 0. Organo-ditellurides, molecules that contain a Te-Te bond, would be appropriate for the crosslinks as their σ*<sub>Te-Te</sub> ← n<sub>Te</sub> transition usually absorbs light between 400 and 500 nm, and can lead to photodissociation of the chalcogen-chalcogen bond.</p> <p>Initial attempts to directly functionalize a polymer (polystyrene) resulted in intractable solids. A more promising approach relies on the preparation of cross-linking agents followed by co-polymerization. Despite literature claims, to date, there is no structurally authenticated photoresponsive molecule that simultaneously contains vinyl (CH=CH) and telluride (-Te-) functional groups. The work in this thesis has yielded what would be the first example, in addition to a crystal structure obtained by X-ray diffraction, the compound has been characterized by multinuclear NMR (<sup>1</sup>H, <sup>13</sup>C, <sup>125</sup>Te) and vibrational spectroscopy with the support of DFT calculations.</p> / Master of Science (MSc)

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