M.S. Theses

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An investigation of the effect of CD, HG and ZN on the growth of two species of blue green algae
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1983., 1983.) Ağlarca, Zeynep.; Çalgan, Dilek.
In this research, effects of three metals, cadmium, mercury and zinc were investigated on two species of blue green algae, Anabaena flos aquae and Gloeocapsa. Cells were grown in sterile medium free of combined nitrogen and under continuous illumination. Metal ions were introduced as chloride salts and different concentrations of the metal ion solutions were used. Absorbance and cell counts were determined for each concentration of the metal ion solution and results were evaluated in terms of these two criteria. Zinc was found to be the most toxic metal for both Anabaena flos aquae and Gloeocapsa whereas the other metals showed inhibitory and stimulatory effects depending on the concentration of the metal ion solution. This showed that effect of the metal whether inhibitory or stimulatory is dependent on the species used and the metal ion itself.
Preparation and properties of white-pine-PMMA composites
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1983., 1983.) İnhan, Günseli Ayşe.; Küsefoğlu, Selim.
Wood-polymer composites fromTurkish White pine (pinea siber)-Polymethylmethacrylate (PMMA), are prepared by heat catalysis method. Monomer loss during polymerization i s prevented by impregnation of wood in PMMA + MMA solution and subsequent polymerization. Volatility of MMA is decreased in a significant degree. % conversion values greater than 85% are obtained. A.S.E. values are determined. It is observed that A.S.E. values for PMMA-MMA impregnated, polymerized samples are higher than pure MMA impregnated, polymerized ones, probably due to MMA shrinkage during polymerization which occurs less in the first case. A.S.E. values greater than 70% are observed for 70% polymer load for PMMA-MMA impregnated samples. Different results are obtained for hardness parallel to grain and for hardness perpendicular to grain. An increase of about 2 fold is observed in case of hardness perpendicular to grain whereas i n case of hardness parallel to grain a 3 fold increase is obtained. Staining wood samples with Rhodamine B dye and subsequent examination under U.V. showed that PMMA had penetrated inside the wood and polymer distribution was mainly along the grain.
Preparation of oleophilic perlite by polymer encapsulation
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1985., 1985.) Bayraktar, Durata.; Küsefoğlu, Selim.
A new oil adsorbing material was synthezised' using expanded perlite . To render perlite oleophilic and hydrophobic it was coated with a suitable hydrocarbon polymer. Perlite was first size classified to assure uniformity and purified from metallic oxide impurities by floatation in ether. After evaporation of adsorbed atmospheric water- it kiss coated using different polymers and different methods. Four subtances were chosen for coating: paraffin, polystyrene, high molecular weight polyethtylene and low molecular weight polyethylene. These substances were solvent deposited on perlite usingappropriatesolvents at suitable temperatures and the solvent was subsequently evaporated. Paraffin due to its volatility could be vapor deposited on perlite under vacuum without the use of solvent. Both paraffin and low molecular weight polyethylene were melt deposited on perlite because of their low melting temperatures. Using these techniques samples with various levels of coating of each material were obtained. These samples were then tested for their oil and water adsorption capability. Further they were conpared among themselves with respect to oil adsorption and cost to choose the best adsorbent. A coating method was also chosen to optimize cost and ease o f manufacture using t h e adsorbent with the highest oil adsorption capacity . Reproducility of the above experiments was tested to calculate accuracy and precision of the work performed. The best adsorbent was found t o be the 48 % low molecular weight polyethylene coated perlite obtained by the melt deposition method. The solid material thus prepared adsorbs 7.4 times its weight in liquid oil, no water, and costs about 108 TL/ Kg. Finally the capacity of the 48% low molecular weight polyethylene coated perlite for hydrocarbon vapor adsorption was tested by passing n-heptane saturated a i r through it. The material adsorbed about one to two its weight in gaseous hydrocarbon. The results were as expected : coating perlite with hydrocarbonlike polymers considerably decreased its water affinity and increased tremendously its oil adsorption capacity. This new material can be used as an efficient sorbent for adsorbing oil and other non-polar organic substances from water surfaces and city water, as well as hydrocarbon vapors from flue gases. It can probably be used in any field requiring oil or non-polar substance removal.
Trace element analysis of metallic artifacts from Gedikli hoard by atomic absorption spectroscopy
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1985., 1985.) Benglian, Ani.; Özbal, Hadi.
The object of this study was to determine the trace and alloying elements of the metal artifacts recovered from Gedikli during excavation between 1964-1967. Most of the artifacts were from a cremation burial sight dated to Early Bronze Age, which includes pins, awls, ring , bracelets etc. About 20-25mg. samples, obtained from over 100 artifacts by drilling, are analysed using atomic absorption spectroscopy. The results showed that most of the samples were copper and copper alloys. Both tin and arsenic were present as an alloying element in some samples at about 7% and 5% respectively. Nearly half of the objects had both tin and arsenic together but at about 1% or less.Silver and iron were the other two elements that were present in almost all samples at trace levels. Zinc and lead concentrations were quite variable from trace levels to up to 27,4% and 15,5% respectively. Artifacts are classified according to type, shape and to presence or absence of certain elements. Histograms, correlations and cluster analysis were carried out on the trace element distribution of these groups to determine particular trends, manufacturing techniques and common are sources. The results showed that, there was no general trand in the trace element distribution in general for all artifacts. However, certain trends could be observed when artifacts are arrand-ged into subgroups. Umbrella headed pins were all tin bronzes with similar trace metal distribution. Two clusters were also observed between artifacts having tin, arsenic, lead and nikel elements which may indicade two different are sources. Even though the artifacts recovered, cover a relatively short time span, the heterogeneity of the trace element distribution could be an indication of different are sources, manufacturing techniques and trade routes. A complete examination of the sight will show if the objects are locally manufactured or not. Chronological arrangement of the artifacts would yield information on the technological development as well as on trade relations. This preliminary study shows that complete excavation of Gedikli could bring light to the metallurgy of the Bronze Age in the area.
The predicted environmental distribution of substituted benzene derivatives
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1986., 1986.) İşeri, Reyhan.; İnel, Yüksel.
The aim of this study is to calculate environmental equilibrium distributions of substituted benzenes and thus to indicate where each of them goes and what relative concentrations they adopt i n the environmental compartments. With the diversity of chemicals, reasons for predicting their environmental behaviour from their physicochemical properties such as vapor pressure, water solubility and n-octanol-water partition coefficient are obvious. In this study, Mackay's Level I Fugacity Model based on fugacity, a thermodynamic quantity related to chemical potential or activity that characterizes the escaping tendency from a phase, is used for calculations. The fugacity calculations are applied to an evaluative environment, " unit world" consisting of compartments of homogeneous air, soil, water, biota, suspended solids and sediment. Each compartment is assigned a reasonable volume and properties and I the equilibrium distributions of those chemicals are calculated using fugacity capacities that are calculated from physical and chemical data and partition coefficients. When the results are designed to yield priorities for each compartment, it is found that alkyl benzenes except butylbenzenexylenes, mono- and di -fluorobenzenes, mono- and di-bromobenzenes , mono-, di- tri-chlorobenzenes, iodobenzene for the air compartment, all phenols, all anilines , acetophenone, benzylcohol, butylbenzene, anisle, nitrobenzenes , diiodobenzenes , chlooiodobenzenes, bromoi odobenzenes, bromochl orobenzenes, iodobenzene, di bromobenzenes , tri bromobenzenes for the water compartment, diiodobenzenes, tribromobenzenes, hexachlorobenzene, bromoiodobenzenes, chloroiodobenzenes, tetrachlorobenzenes, pentachlorobenzene.for the biota, soil , sediment, and suspended solids compartments are priorities. During this work, good correlations between the mass partitioning of halobenzenes and total molecular surface area, molar volume and T hydrophobic substituent constant are obtained. The mass percentage values calculated by using the correlation equations obtained from this study are in agreement with those calculated through Mackay's Level I approach. Thus these correlations make it possible t o calculate the likely equilibrium distribution by using only one property.
A parametric study of laboratory scale manifacture of sodiumallysulfonate
(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Scieence and Engineering, 1986., 1986.) Börekcioğlu, Pınar.; Arıcan, Haluk.
The main aim of this work involyes the manufacture of sodium allylsulfonate from allylbromide and sodium sulfite by using laboratory scale testing of the commonly used industrial batch method(1). Yield of sodium allylsulfonate by processing conditions were examined. Sodium allylsulfonate (SAS), is mainly used in nickel electroplating bath as a brightening and levelling agent . It improves the throwing power of thebath, thus; yielding deposits of high brightness and good adherence. At the same time, it possesses the other properties of brightening agents by being a rapid adsorber on the cathode withit subsequent incorporation into the electrodeposit. It has strong inhibition action on the discharge of nickel ions without significantly affecting the discharge of hydronium ion . SAS also possesses the ability to considerably decrease the Nickel current efficiency within crease in SAS concentration in the electrolyte. Sodiumallylsulfonate, besides the other unsaturated sulfonates, is an important copolymerizable emulsifying agent in copolymerization with larger proportions of acrylonitrile for the preparation of dyeable acrylic fibers with improved whiteness. Because of the molecular structure; having a double bond; a sulfonate group and low molecular weight, Sodiumallylsulfonate is the preferred copolymer among the other unsaturated sulfonates. The compound was synthesized by using a new reagent other than recommended in literature. Allylbromide was used instead of allylchloride and methanol was used as the solvent in the reaction mixture. The analysis of the samples obtained from experiments, showed the identical properties with the commerciallyl used sample synthesized by allylchloride as the primary reagent. A number of experiments were carried out based on the same procedure but with different experimental reaction parameters . Physical and chemical tests were carried out on the products obtained . A process was then chosen to optimize the cost and ease of manufacture with the optimum results. The repetition of the experiments at the selected reaction conditions were examined, and it was found that at 44 and 180 minutes of reaction time the best yield and quality of SAS samples were obtained.
The effect of selected pesticides on the growth and nitrogen fixation in cyanobacteria
(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1992., 1992.) Güner (Sıvacı), Sima.; Çalgan, Dilek.
Algae, in general, are the primitive form of higher plants and they are found in water bodies and in moist locations such as tree trunks, walls, rocks and damp soil. Many species are found in all parts of the world, from the tropics to the polar regions. Water , light, temperature and the chemical composition of the medium are the factors that may stimulate or prevent the growth. The elements essential for the growth of algae are the same as those necessary for the growth of higher plants. Algae are used for the removal of pesticides from the aquatic environment, therefore their functions and responses to external effects resulting from the use of chemicals are of concern. The choice of algal species for bioassays is partly based on algae being the primary producers in aquatic ecosystems. Since pesticides are pollutants, it is better to analyze them on these living organisms, which can give an information about other higher plants. Contamination of aquatic and soil environments by pesticides results from agricultural origin. Pesticides enter the environment by direct or indirect routes. These agents can be sprayed on crops or dispersed in the field as a granular substance. Such pesticides are introduced directly into the aquatic environment. The cleaning of industrial mixing equipment, disposal of waste and accidents increase the amount of pesticides found in soil and water. Rain and other precipitation can carry pollutants to the fresh water systems, so causing harmful effects for the algae. The application of pesticides for plant protection and their persistent residues has direct effect on the fresh water algae and consequently the soil fertility. These pesticides applied directly or indirectly to soil may upset the ecological balance of the soil. This situation clearly explains the importance of studying the effects of pesticides on the different physiological and biological processes. Algal studies are recently well documented. Recent studies involve the use of some pesticides on algal cultures in order to examine their effects on growth and nitrogen fixation. Effects of chemical agents could quickly be investigated with blue-green algae before testing pesticides on higher plants. The aim of this study was to examine the toxicity effects of a herbicide 2,4- dichelorophenoxyacetic acid (2,4-D) and an insecticide methyl parathion on two algal species, one being a heterocystous filamentous cyanobacteria Anabaena cylindrica and the other, unicellular cyanobacteria Gloeocapsa. Toxicity determinations were based on the growth measurements of these species. Moreover, a specific property of blue-green algae, nitrogen fixing ability was determined by using acetylene reduction technique. During the experiments light intensity, temperature and pH were under the control.
Heterogeneous photocatalytic activity of transition-metal cation impregnated TiO2
(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1993., 1993.) Rakshandeh (Bazargan), Parisa Deljouie.; İnel, Yüksel.
Irradiation of aqueous Ti02 dispersions containing metal ions with light of energy equal or greater than the bandgap of the catalyst. leads to a deposition on the semiconductor particle surface. This photodeposition process may be a phtotoreduction or an irreversible photosorption process depending on the redox potential of the couples in the solution. In this study, preparation of Ti02 impregnated by some selected cations of the first transition series: ( Cr(III), Mn(II), Fe(III), Fe(Il), Co(II) and Ni(II)] using dark and photocatalytic impregnation methods has been demonstrated. and the photocatalytic activity of these samples in photodegradation of 4-chlorophenol in aerated aqueous solutions has beeinvestigated by gas chromatography techniques. The effect of sulfate anion on the degree of 4-chlorophenol photooxidation to C02 has also been studied by the same method. The addition of alcohols, which scavenge the holes of the illuminated TiO2 renders the photodeposition process more efficient by preventing the recombination of holes with electrons on the catalyst's surface. This effect has been examined by using methanol as a model hole scavenger. Finally, BET surface areas for Co(II) and Ni(II) impregnated Ti02 samples were measured in a Micromeritics Flowsorb II 2300 instrument.
Photocatalytic degradation of phthalic anhydride and dicarboxylic acids
(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1994., 1994.) Ökte, Ayşe Neren.; İnel, Yüksel.
Exposure of Ti02 particles to light with an energy equal or greater than its bandgap leads to the creation of electrons and holes which are able to degrade toxic chemicals. In this study, in the presence of Degussa P25 TiO2, photocatalytic oxidation of phthalic anhydride, malonic acid, succinic acid, and adipic acid has been investigated by means of gas chromatography techniques following the CO2 formation. The alteration of pH of the aqueous suspension, TiO2 loading, anhydride or acids concentrations, irradiation time, flow rate, and light intensity changed the rate of formation sf C02 which has been investigated by the same method. It was also observed that the rate of CO2 formation increases linearly by increasing the temperature sf the suspension. The order of the reactions as well as the rate constants could be determined for the photocatalpic oxidation processes. As a consequence, by altering the concentration of malonic, succinic, and adipic acids we observed that their disappearance fits a Langmuir-Hinshelwood kinetic model. In other words, the photoocatalytic xidation reactions take place in the adsorbed phase, i.e., on the surface of Ti02. Rate constants was also calculated by including the correction term a(T) which stands in order to take into account the decrease in the solubility of CO2 with increasing temperature. These results led to the calculation of activation energy as: 3.19 kj/mole, 9.99 kj/mole, 15.59 kj/mole, and 14.38 kj/mole for phthalic anhydride, malonic acid, succinic acid, and adipic acid respectively. Finally, 0.43X10 -6 quantum yield for the CQ formation has been estimated from the proposed mechanisms.
Conformational analysis of 2-[(4-substituted-phenyl)seleno]-1,3-dithianes: |a theoretical approach
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Sciences and Engineering, 1997., 1997.) Şenyurt, Nurcan.; Aviyente, Viktorya.
In this study the conformational analysis of 2-(4-substituted-phenyl)seleno-1,3-dithiane with H, Cl, F, CH3, CF3, NO2, OCH3 and N(CH3)2 substituents have been studied computationally both in gas phase and in solvent with the semi-emprical PM3 method and ab initio HF/6-31G* basis sets. The optimized geometries have been discussed in terms of endo and exo anomeric effects and their presence in the axial conformers have been confirmed. The conformational free energies have been calculated in gaseous phase in solvent. Comparison between experimental and calculated values has shown that PM3 as well as HF/6-31G* can be used confidentially to treat conformational equilibrium for cyclohexane derivatives with S and Se.
Removal of impurities from copper and its alloys using ancient refining techniques
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Sciences and Engineering, 1998., 1998.) Uluocak, Berivan Bilge Gedik. .; Özbal, Hadi.
There were two major objectives of this study both related to purification of impure copper metal using primitive refining techniques believed to have been used in antiquity. First part of the study was to remove iron impurity from bronze that is introduced when iron containing tin (hard-head) is used as source of tin. In the second part, simple refining methods are applied to highly impure copper metal obtained by smelting polymetallic copper ores. "Hard-head" which is a mixture of iron-tin compounds are biproduct of tin smelting process where cassiterite is contaminated with iron oreas. It was not possible to remove all of the tin held in hard-head and some tin is inevitably lost. Hard-head prills were prepared composed of 20 per cent iron ans 80 per cent tin under controller conditions, in clay crucibles. The hard-head prills were then added onto the molten copper metal in the furnace at 1200C. since all compositions of Sn-Fe compounds at 1200C and Cu and Fe does not make an alloy, tin is expected to be extracted by copper while rejecting the iron from the medium. The iron was then oxidized selectively either by the addition of natural fluxes (powdered marble and sand) or by fire-refining method. Experiments were carried out and it showed that, under addition of suitable fluxes, it was possible to remove over 85 per cent iron present in hard-head, leaving the concentration of iron in bronze under 0.5 per cent. The loss of tin, however was less than 20 per cent. It is concluded that unrefinable hard-head can be economically used in the production of bronze. Most primary copper ores are polymetallic in character and contains iron, lead, arsenic, nickel, antimony and zinc in varying amounts. There is ample evidence that such ores were smeltedtogether in antiquity yielding highly impure copper metal containing Pb, Zn, Sb, Ni, and Fe. To use such copper, it must be excessively refined. Fire refining methods were applied on the purification of impure copper that contains 20 per cent Pb, 5 per cent Zn, 5 per cent Sb, 2 per cent Ni, and 3 per cent Fe. Without any flux and using only air blast on the molten alloy, it was possible to remove about all of iron and zinc, and up to 50 per cent of the Pb, Sb, and Ni.
The isolation and identification of sesquiterpene lactone constituents of the plants Centaurea Cheirolopha Wagenitz and Centaurea Cuneifolia sm.
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1998., 1998.) Yetüt, İzlem.; Halfon, Belkıs.
The aim of this study is the isolation and identification of the physiologically active terpenic constituents of the plants Centaurea cuneifolia Sm. (Compositae) and Centaurea cheirolopha Wagenitz (Compositae). Former studies with Centaurea species have resulted in the identification of terpenoids as well as flavonoids and other natural compounds. Centaurea cuneifolia Sm. yielded two sesquiterpene lactones which have been identified on the basis of Infra Red and Nuclear Magnetic Resonance Spectra. The two sesquiterpene lactones identified are Dihydromelitensin and 8a-(3,4-dihydroxy-2-methylene butanoic acid) ester of Dihydromelitensin.Centaurea cheirolopha Wagenitz yielded four sesquiterpene lactones. Infra Red, Nuclear Magnetic Resonance, and Mass Spectra have been used in the identification of the four sesquiterpene lactones, namely Aguarin B, Cynaropicrin, 8a-(2,3-dihydroxy-2-methyl propanoic acid) ester of Zaluzanin-C and 15-deschloro-15-hydroxychlorojanerin. Eventhough 15-deschloro-15-hydroxychlorojanerin has been formerly isolated from other plant species, this is the first study where it has been isolated from Centaurea species. The structure of this sesquiterpene lactone has been identified on the basis of 13C NMR (Attached Proton Test-APT) in addition to the previous spectroscopic methods.
Reactions of dichlorozirconocene with nitrogen containing heterocycles and related compounds
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1999., 1999.) Ünal, A. Özge Akdeniz.; Bulak, Ece.
In this study the reaction of 16 e- system, dichlorobiscyclopentadienyl- zirconium(IV) with N-containing, S-containing and thioamide containing ligands were studied. In the presence of a non-coordinating solvent, CH2Cl2, thioacetamide coordinated to Cp2ZrCl2 through C=S unit with participation of the NH group. This complexation was proved by the new bands appearing in Zr-N and Zr-S stretching region, also by the blue shift of thioamide band I and the red shift of thioamide band IV of thioacetamide. Deprotonated ethanethiol with Cp2ZrCl2 gave a dimeric complex with the formula (Cp2ZrClSCH2CH3)2. Without deprotonation ethanethiol did not coordinate to Cp2ZrCl2.
Conformational equilibria of alpha-substituted cyclohexanones with different chalcogens (O, S, Se)
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1999., 1999.) Duran, Emine Sevim Dilek.; Aviyente, Viktorya.
The conformational analysis of alpha-substituted cyclohexanones with different chalcogens (OH, SH, SeH, OC6H5, SC6H5, SeC6H5) has been studied in gas phase with semi-empirical PM3 and ab initio HF/6-31G*. The para F, Cl, Br, NO2, NH2, OCH3, alpha-phenoxy, alpha-phenylthio and alpha-phennylseleno substituted cyclohexanones have been investigated in gas phase. The optimized structures (alpha-OH, SH, SeH, OCH3, SCH3, SeCH3, OC6H5, SC6H5, SeC6H5) have been analyzed in polar medium using a continuum Self Consistent Reaction Field (SCRF) model. Computations have provided data on the structure, the dipole moments and the thermodynamic properties of the compounds of interest. Justification of the experimental results has been followed by predictions on similar substituents and overall generalization.
Synthesis and polymerization of plant oil monoglyceride maleates
(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1999., 1999.) Can, Erde.; Küsefoğlu, Selim.
In this study, rigid thermoset polymers were synthesized from radical copolymerization of the soybean oil monoglyceride maleates with styrene. In the first part of the study, soybean oil monoglycerides (SOMG) were obtained from the reaction of soybean oil with glycerol at 220-2400C. An optimization of the glycerolysis reaction was achived through the use of a large amount of excess glycerol and with a rapid cooling process at the end of the reaction to maximize the monoglycride yield. In the following step, soybean oil monoglycerides (SOMG) were reacted with maleic anhydride at temperatures around 1000C to produce the SOMG maleate half esters. Different catalysts and different reaction conditions were examined to increase the maleate half ester's yields. The reactions were followed by IR and 1H-NMR and the products were charecterized by mass spectrometry. In the final step, the radical initiated copolymerization of the SOMG maleates with styrene produced rigid, thermoset polymers. The SOMG maleates were found to be effective emulsifying agents, thus the emulsion copolymerization of the SOMG maleates with styrene was also carried out successfully without the addition of an emulsifier. The obtained polymers were characterized by IR and 1H-NMR, the cross linked net work structure of the coploymers was examined with the swelling behaviour in different solvents. The resulting copolymers of SOMG maleates with styrene are suitable for fiber reinforcement and can be used as a liquid molding resin with the right fiber reinforcement.
Scrap rubber recycling in nitrile rubber composites
(Thesis (M.S.) - Bogazici University. Institute for Graduate studies in Science and Engineering, 2001., 2001.) Şahin, Yeşim Müge.; Nugay, Nihan.
In this study, scrap rubber were recycled by blending with nitrile rubber composites, having carbon black as filler. Resulting composites have been investigated, in terms of rheological and dynamic-static mechanical properties as well as their dimensional stabilities in organic solvents, as a function of carbon black-ground rubber compositions together with the size of ground rubber and their surface modification. Results have shown that, replacement of carbon black with ground rubber in a composite, has performed more reasonable rheological properties as well as improved dynamic properties, with respect to the composites having only carbon black as filler. The loss in swelling and some static mechanic values of the composites due to this replacement, can be tolerated by using small-sized and silanized ground rubber. In the light of this study, it has been observed that by tailoring the composition, size and modification of ground rubber, it is possible to obtain composites having optimum rheological and mechanical properties, maximum vibrational damping capacity as well as minimum swelling in hydrocarbon media.
Stereoisomers resulting from the hindered rotation in N-(o-ARYL)-2,4-oxazolidinedione derivatives
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2001., 2001.) Ordu, Öznur Demir.; Doğan, İlknur.
In this study, sterically hindered 5-methyl-3-(o-aryl)-2,4-oxazolidinediones and 5,5-dimethyl-3-(o-aryl)-2,4-oxazolidinediones have been synthesized by the reaction of the o-aryl isocyanates with (S)-(-)-ethyllactate or ethyl á-hydroxyisobutyrate, respectively.Diastereomeric isomers of the 5-methyl-3-(o-aryl)-2,4-oxazolidinediones have been detected by using 1 H NMR. Enantiomeric isomers of the 5,5-dimethyl-3-(o-aryl)-2,4-oxazolidinediones have been identified by 1 H NMR and 13 C NMR, also in the presence of the chiral auxiliary. Activation barriers to hindered rotation around C-N single bond have been determined for o-methyl and o-chloro substituted enantiomers by using DNMR. The conformational preferences of the diastereomers have been investigated by 1 H NMR and by HPLC on an optically active sorbent. The rotation in the o-fluoro derivatives was found to be too fast to make the rotational isomers observable by NMR, whereas the rotational isomers of the ortho bromo compounds were found to be separable at room temparature. Using HPLC on cellulose carbamate the isomers were separated and for the diastereomeric isomers of 5-methyl-3-(o-bromophenyl)-2,4-oxazolidinedione, the equilibrium constant and the energy barrier for the conversion of the less stable conformation to the more stable one were determined by following the equilibration of the isomers at constant temperature.In addition, the reactions of halogen substituted 5-methyl-3-(o-aryl)-2,4-oxazolidinediones with methanol have been studied. The compounds were found to react with methanol, causing a ring opening reaction. The products were identified by 1H NMR.
Thermoset polyester with phase changeable fillers for heat storage
(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2003., 2003.) Çaylı, Gökhan.; Küsefoğlu, Selim.
In this study, emulsions and sols of unsaturated polyester, containing phase changeable fillers (PCM) PEG-4000, paraffin, and Wood's metal, were prepared. Unsaturated polyester was the continuous phase and fillers were the discrete phase. These fillers were well distributed and dispersed in unsaturated polyester. Emulsions and sols containing different proportions of fillers were prepared, and the continuous phase was cured with initiator, methyl ethyl ketone peroxide (MEKP) and accelerator; cobalt naphtanate. After curing, the product becomes a thermoset polyester composite which was filled with homogenously distributed PCMs. Mechanical, thermal properties, and surface hardness of cured material were examined. DMTA (Dynamic Mechanical Thermal Analysis), DSC (Differential Scanning Calorimeter), SEM (Scanning Electron Microscope), and shormeter were used for these purposes. The mechanical properties of cured resins vary with PCM content. In paraffin and Wood's metal filled samples, the filler is a load bearing component. At phase change temperatures of the fillers, the samples show observable changes in dynamic mechanical properties. Maximum working temperatures of cured samples also decrease with increasing filler amount. Neat polyester does not show any melting transition, however, paraffin and Wood's metal filled samples show melting transitions. PEG-4000 filled samples do not show melting transition. Around the melting point of fillers materials absorbs a certain amount of heat. Except PEG-4000 filled samples, paraffin and metal filled samples show an endotherm around the melting point of filler while materials themself show no indication of melting externally and retain their physical shape.
Synthesis and photopolymerizations of new methacrylate crosslinkers and antibacterial quanternary ammonium monomers
(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2004., 2004.) Ayfer, Burcu Sunam.; Avcı, Duygu.
In the first part of this work, new amine monomers were synthesized from the reaction of 3-(acryloyloxy)-2-hydroxypropylmethacrylate (AHM), acrylamide and methacrylamide with various amines and then reacted with various alkylhalides to give six new quaternary ammonium monomers. The photopolymerization of the monomers was investigated by photo-DSC at 30 0C. The reactivities of quaternary ammonium monomers were highly depended on monomer structures. The antibacterial activities of the synthesized amine and quaternary ammonium monomers, their homopolymers and copolymers with 2-hydroxyethylmethacrylate (HEMA) were investigated using S. aureus and E. Coli. It was found that as the alkyl chain length increased, the antibacterial activities of methacrylamide-pyridine QACs increased.In the second part of this work, three new ester-linked diacid monomers and two ether-linked diacid monomers were synthesized from the reaction of succinyl chloride, adipoyl chloride and dodecanedioyl dichloride with tert-butyl ?-hydroxymethyl acrylate and Bisphenol A and triethyleneglycol with tert-butyl ?-bromomethyl acrylate followed by hydrolysis of t-butyl groups with CF3COOH. The structure-reactivity relationship of the monomers was investigated using photo-DSC. TBHMA-Succinyl diacid monomer had highest reactivity and conversion at 40 0C. All monomers showed higher rates of polymerization at 60 0C than the those of 40 0C. Incorporation of 2 per cent crosslinker to HEMA increased the rate of polymerization.
Modeling the structure-reactivity relationship of acrylates
(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2005., 2005.) Değirmenci, İsa.; Aviyente, Viktorya.
Photoinitiated polymerization of acrylates is one of the most common processes for therapid production of polymeric cross-linked materials with defined properties. Acrylicmonomers have different reactivity behavior during the free radical polymerization depending on the position of substituents on the monomer. In this study, the free radical polymerizationof alkyl ??-hydroxymethyl acrylates, itoconic acid derivatives and substituted methyl acrylatesare modeled by using the ab initio (B3LYP/6-31G*) quantum mechanical calculations.Transition states for the radical addition, the chain transfer and the disproportionation reactions are located. The reaction rates are calculated by using the classical Transition StateTheory in order to understand the structure-reactivity relationship of acrylates. The variablessuch as the activation energies, the entropy of transition states and the Boltzmann averageddipole moments of the monomers are discussed. The lability of the hydrogen atoms in the monomers and radicals has been determined. The disproportionation rate constant, kd, is usedin the kp/kt1/2 ratio to evaluate the rate of polymerization. It has been found that in generalbulky groups decrease the rate of polymerization while electron withdrawing substituents and polar molecules enhance the polymerizability of the monomers.

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