Theses supervised by Doç. Dr. Ali Ersin Acar
20 theses · Boğaziçi University
Synthesis of novel pressure sensitive adhesives for label applications
In the label adhesives industry, the accepted pressure sensitive adhesives (PSA) are acrylic based water dispersions. These acrylic polymer emulsions have excellent ultraviolet (UV) and chemical resistance. However, their adhesion values alone are not enough for market requirements. Due to this, producers compound these acrylic polymers with tackifier resin dispersions especially for paper labels. In this study, it is aimed to produce label adhesive using a new approach. The goal is to develop a new one-pot polymerization process for the filmic label market. In one pot system, the purpose is to synthesize ready dispersions for label adhesives by adding the tackifier resin during the polymerization to the acrylic monomer. By doing so, it is hoped to eliminate high cost dispersing machines and high level of surfactants used in the dispersion process of the tackifier resin. Elimination of the surfactant coming from the tackifier resin dispersion is a potential solution for the whitening problem of the filmic labels. Another advantage is to save energy from the high cost dispersing process
Synthesis of isoquinoline and pyrocatechol derivatives as potential drug molecules active against prostate cancer
Prostate cancer is one of the most common cancer types among male worldwide. It has been found that about 80 percent of prostate cancer patients have high level of androgen levels. Prior researches have stated that reducing the androgen level in the body can be a good solution to prevent the growth of cancer cells. Androgens are synthesized in both testes and adrenal glands. Hence, inhibition of androgen biosynthesis in not only testes, but also adrenal glands is essential to suppress the androgen biosynthesis. The last step of androgen biosynthesis in both testes and adrenal glands is catalyzed by a single enzyme, 17?-hydroxylase-17,20-lyase (CYP17). On account of this information, selective inhibition of CYP17 enzyme results in reduction or complete annihilation of androgen production. Thus, CYP17 is the foremost target enzyme for the treatment of prostate malignancy. Accordingly, computational screening method was used to find out lead compounds active against CYP17 enzyme by Prof. Metin Türkay and Assoc. Prof. Halil Kavaklı from Koç University. As a result of the drawbacks of steroidal compounds, a non-steroidal lead compound with an IC50 value of 35 µM was found. In order to find compounds with better IC50 values, derivatives of the lead compound were examined by using Autodock program. Among the derivatives, the compounds with better docking and binding energies were synthesized. In this project, synthesis of isoquinoline and pyrocatechol derivatives was targeted. For this purpose, ten compounds were synthesized. Biological tests were performed by the research group of Assoc. Prof. İbrahim Halil Kavaklı from Koç University. As a result, a new compound with hundred percent inhibition at 5 µM concentration was discovered.
Synthesis of novel pressure sensitive adhesives by emulsion polymerization technique
Acrylic based water dispersions are commonly employed in label adhesive industry as pressure sensitive adhesives (PSAs). Although acrylic polymer dispersions have excellent chemical and UV resistance, they cannot fulfill the desired performance requirements of the market. Because of this reason, acrylic polymer dispersions are compounded with tackifier resin dispersions by the PSA producers. However this compounding process requires use of high performance mixers which costs a lot, and use of high amount of surfactant which causes whitening problem in label adhesives when in contact with water. In this study one pot emulsion polymerization technique in the presence of a tackifier was employed to synthesize acrylic based pressure sensitive adhesives for filmic label market which should in principle, eliminate the use of high cost mixers and high amounts of surfactant and thus solve whitening problem of the filmic labels.
Synthesis of a novel formaldehyde-free crosslinker for waterborne binder dispersions in textile industry
Binders are emulsion polymers used in textile and nonwoven production to impart integrity, strength and durability. However, binders that do not have reactive functional monomers in their formulations are not efficient enough to provide these properties. Addition of self-crosslinking monomers to the binder system is a common method to improve the properties of textile and nonwoven products. Textile industry has used monomers such as n-methylolacrylamide (NMA) as functional group to crosslink upon curing. But, this crosslinking mechanism has a by-product. NMA generates formaldehyde when it is heated to crosslink. Formaldehyde remains in the products in which binders are used or is released into the environment. According to the 12th Report on Carcinogens published by the U.S. Department of Health and Human Services, formaldehyde is a substance listed in the category of known to be a human carcinogen. Because of its toxicity, reduction or elimination of formaldehyde emission is one of the focal points of development in textile industry. In this study, a novel formaldehyde-free crosslinking monomer was synthesized for waterborne binder dispersions and its performance was evaluated in comparison with NMA.
Synthesis of a novel benzophenone derived UV absorber acrylate monomer
Since the destructive effects of sunlight have been discovered, UV protection of materials have gained more importance. The weathering resistance of organic materials can be increased by coating their surface with UV absorber polymers. Benzophenones and triazines are the most common commercially availible UV absorbers which are sold under different trademarks. In this thesis, we have synthesized a novel benzophenone derived acrylate monomer which undergoes Photo-Fries Rearrangement when exposed to sunlight. The new compound has the ability to absorb the UV portion of the electromagnetic spectrum via proton transfer. When the radiation stops, the compound returns to its original form and release the energy as heat so that the material is protected from the UV light. The monomer was polymerized to give homopolymers and methyl methacrylate copolymers at different ratios, then the UV absorption behavior of the polymers before and after the UV radiation were investigated.
Synthesis and characterization of precursors for quinoxaline cyclization
Quinoxaline compounds are essential nitrogen containing heterocyclic compounds of various biological properties and have several pharmaceutical applications. In this work, several precursors to be used in quinoxaline cyclization were synthesized from diamine- and tetra-aminobenzene hydrochloride precursors. Our group added several substituents to phenylenediamine or used directly 1,2,4,5-Benzenetetramine tetrahydrochloride before a coupling reaction with 1,2-Acenaphthylenedione. The systematic characterization of the quinoxaline derivatives and final products were done via 1H-NMR and13C-NMR.
The synthesis and thermal characterization of tri-substituted triazines
Cyanuric chloride has huge application areas in chemical industries on drug, agriculture, polymer, dye and leather because of fact that cyanuric chloride is commercially cheap. In addition to this, its substitution reaction can be controlled easily via temperature. The most variety of application is in polymer industry. One of the applications of cyanuric chloride is polymerization of substituted s-triazines via a monomer with a nucleophilic group or end capping. In this study tri-substituted triazines were synthesized starting from cyanuric chloride and their thermal behavior were investigated in the presence of different nucleophiles to predict their potential for polymerization through trans-esterification reactions.
Synthesis of isoquinoline derivatives as potential drug molecules active against prostate cancer
Cancer is the most common neoplasm of the prostate in developed countries. About 80% of prostatic tumors are based on elevated levels of androgens because androgen stimulates the cellular proliferation of human prostate cancer. Therefore, deprivation of androgen level constitutes a good strategy in order to treat castration-resistant prostate cancer. Enzymes in androgen biosynthesis are favorable targets, such as CYP17A1. Although the androgens are secreted from three different sites, namely the testes, adrenal glands, and PCa cells, androgen production depends on catalysis by one enzyme, CYP17, which is also known as P450-C17. Being a pivotal enzyme in the biosynthetic route to steroidal hormones, CYP17A1 has a key role in the conversion of progesterone and pregnenolone to androstenedione and dehydroepiandrostenedione (DHEA) respectively, which constitute as the direct precursors of 5α-dihydrotestosterone (DHT) and testosterone (T). Since the crystal structure of CYP17 has been absent for a long term, natural substrates (pregnenolone and progesterone) have been used as scaffolds of potential drug candidates. Although Abiraterone was launched as a potent steroidal CYP17 inhibitor, due to the potential side effects of steroidal CYP17A1 inhibitors resulting from inhibition of other steroid receptors, there is a certain need to develop nonsteroidal inhibitors. In this project, several derivatives of a nonsteroidal lead compound were designed: Mainly the synthesis of isoquinoline derivatives was endeavored. Besides, a library of final products was built by synthesizing several aromatic carboxamides including benzofuran-2-carboxylic acid, benzo[b]thiophene-2-carboxylic acid and 4-(1H-tetrazol-5-yl)benzoic acid derivatives.
Screening of various polyethylene terephthalate chain extenders in a melt polymerization set-up
Polyethylene terephthalate (PET) is one of the most important and common polyester in the industry. It is produced by the reaction of ethylene glycol (EG) with terephthalic acid (TPA) or dimethyl terephthalate (DMT). The polymerization can be carried out through melt then, if high molecular weights are targeted, solid state polymerization. PET has excellent chemical resistance, high mechanical strength and high thermal stability. Therefore it is used in very different application areas. For every application area PET have different molecular weight values. As the molecular weight requirement increases the production of PET becomes difficult via melt polymerization. Solid state polymerization (SSP) is used for high molecular weight PET production. SSP's disadvantage is that reaction time is very long and therefore expensive. Also, during processing of PET, molecular weight decreases because of the heat applied. All these problems can be addresed via chain extenders. In this study, chain extension reactions of PET with four different chain extenders, carbonyl biscaprolactam, 1,3-phenylene-bisoxazoline, DE and SO were carried out and their effect on molecular weight were investigated. Structures of DE and SO will not be noted in this thesis due to the confidentiality of the study.
Formaldehyde-free crosslinker synthesis in waterborne binder dispersions for textile industry
In textile industry, the binders used are mostly water based acrylic dispersions. These binders provide strength, elastic recovery, soft hand, flexibility, color retention and also resistance to washing and aging to the textile and nonwoven. Nevertheless, binders having no reactive functional monomers are not very successful in imparting these properties. Self crosslinking monomers are used to improve the properties of textile and non woven end products. N-methylolacrylamide (NMA) is one of these monomers having functional groups for self-crosslinking. However, N-methylol acrylamide used in textile binders emit formaldehyde during crosslinking at high temperatures. This formaldehyde either remains in the end product or is liberated into the air. The U.S. Department of Health and Human Services published the 12th Report on Carcinogens and formaldehyde is listed in the category of known to be a human carcinogen. Researchers on textile sector are focud on the subject of formaldehyde emission due to the harmfull effects on both people and environment. In this study, a novel monomer that emmits no formaldehyde and have ability to self-crosslink was investigated for replacement of NMA and the performance results are compared with that of NMA.
Towards understanding polyethylene terephthalate hydrolysis and aminolysis in tire cords
Polyethylene Terephthalate (PET) is the most common thermoplastic in the industry. It is synthesized via polycondensation reaction between ethylene glycol (EG) and terephthalic acid (TPA) or dimethyl terephthalate (DMT). PET has variety of application areas and it is widely used in tire industry due to its high physical strength and chemical resistance. However, it is subjected to di erent types of degradations during synthesis and processing. PET tire cords su er especially from hydrolytic degradation during vulcanization where green tire is turned into standard tire with sulfur crosslinking with the help of accelerators. The degradation of PET is catalyzed by the released tertiary amines from the accelerators as a result of thermal decomposition. Quaternization was chosen as a method to address the problem which should block the tertiary amines' catalytic activities. TMP was chosen as an agent of methylation/quaternization. TMP was investigated for its methylation ability and chemical properties. Results show that both alkyl and aromatic amines can be quaternized/methylated by TMP. Then the study was focused to poly-2-vinyl pyridine containing latex (VP-latex), a coating used as an adhesion promotor in PET tire cords, which contain pyridine moiety that can potentially react with the TMP as a side reaction. First methylation of 2-vinyl pyridine units in VP-latex was investigated, then, its involvement in hydrolytic degradation was investigated via degradation studies.The results showed that VP-latex was not catalyzing the hydrolytic degradation of PET and it was inert to TMP.
Synthesis of sulfonated polyethylene terephthalate via melt polycondensation
Polyethylene terephthalate (PET) is an essential thermoplastic polyester that used in many industrial applications. The synthesis of PET has two pathways, which are the esterification of terephthalic acid (TPA) and ethylene glycol (EG) or transesterification of dimethyl terephthalate (DMT) and EG. PET can be produced via melt polymerization to obtain low to medium molecular weight. High molecular weight PET requires one additional step, solid-state polymerization (SSP). PET has distinctive properties such as high mechanical strength and solvent resistance. The hydrophobic nature of PET restricts its use in some applications, such as textile, dyeing, adhesion, and water absorption, in which polarity is necessary. Modifying the surface of the PET is necessary to enhance its wettability. In this study, to alter the hydrophobic nature of PET and introduce hydrophilicity, the effect of incorporation of the ionic monomers, SM_1 and SM_2, was investigated. The copolymers were synthesized via melt polycondensation, and their wettability were investigated by using contact angle measurements. The impact of incorporating additional monomers such as diethylene glycol (DEG) and triethylene glycol (TEG) on PET hydrophilicity was studied. Sulfonated copolymers of PET were synthesized on a large scale. Surface modification of PET with sulfonated monomers, DEG and TEG exhibited better hydrophilic properties than the pure PET.
The effects of additives on suspensionpolymerization of styrene and itsoptimizations
Nowadays, the incorporation of several novel additives such as colorants, flame retardants, and graphite into polystyrene is studied to tune its fire resistance, improve its cell structure, optimize its insulation properties, and give it an aesthetic look. However, there are not many studies about the stabilization of suspension polymerization in the presence of different additives, which may alter different features of the reaction, such as its viscosity, its ionic strength, its reaction rate, etc. The driving force of this study is to understand and optimize the reaction and the reaction conditions of incorporating different additives into polystyrene beads via suspension polymerization technique and free radical polymerization in the presence of graphite, colorant and flame retardants. The impact of various additives on the polymerization was systematically investigated, focusing on parameters such as suspension stability, Mw, and Tg. It was observed that the incorporation of different additives caused different viscosity behaviors. The adverse effects of incorporation of different additives were overcome by the addition of polymeric suspension stabilizers and anionic surfactants.
Syntheses of polymers using activated s-triazines and an investigation of s-triazine thermal rearrangement
Polycyanurates hold remarkable potential applications and are worth in-depth research. The study focused on synthesizing a novel s-triazine monomer for the melt polycondensation. The monomer, activated s-triazine, was synthesized in two steps from commercially available starting materials. Activated s-triazine was polymerized with bisphenol-A under reduced pressure in the presence of a basic catalyst. Initial polymerizations were found to show thermal rearrangement, which was further investigated. The thermal rearrangement reaction of s-triazines was studied through thermal exposure experiments, instrumental, and kinetic analyses. To suppress the thermal rearrangement in polycyanurates, solution polymerization at a lower temperature was performed with activated s-triazine in the presence of a basic catalyst.
Polietilen tereftalat sentezinin solüsyon polimerizasyon yöntemi ile incelenmesi
Poly (ethylene terephthalate) (PET) is a thermoplastic polyester commonly used in the industry owing to its good mechanical strength, thermal stability, high solvent resistance and low-cost production. According to application area, various molecular weight PET is produced mostly at high temperature at melt phase under vacuum. Although melt polymerization is feasible and widely used, there are disadvantages of the system such as degradation of PET due to the long reaction time at high temperature and formation of side products such as diethylene glycol. To avoid such degradations, melt polymerization is used to obtain PET's that are considered medium molecular weights then solid state polymerization is employed to produce higher molecular weight PET's. However, SSP requires very long reaction times (12-24 h) which makes it very inconvenient and expensive. Therefore, in the present work, an alternative pathway that could potentially replace the SSP process was investigated. The main goal was to synthesize PET-anhydrides, in other words, polyester anhydrides, that may act as chain extenders when reacted with –OH terminated medium molecular weight PET's. During such effort, syntheses of polyacid anhydrides, then PET polyesters, then finally PET polyester anhydrides were investigated. These reactions were all carried out by solution polymerization techniques which is not a reported technique for the synthesis of PET. The scope and the limitation of such a process for the synthesis, and its effect on the final polymer properties are discussed. The results from templatize chain coupling reactions of PET using the polyanhydrides and polyester anhydrides is presented.
Syntheses of novel acetal-based formaldehyde-free crosslinkers
Crosslinking of polymers is a fundamental process applied in industry to enhance mechanical and physical properties of polymeric materials. Wide variety of crosslinkers are available to be used for this purpose whose structures depend on functionalities of the polymers and desired characteristics of the products. Crosslinkers can be in the form of polymeric or small molecule. As polymeric crosslinkers, formaldehyde based resins and latex binders may be given as examples of commonly used ones in coatings, adhesives and textile. N-Methylol acrylamide is one of the most commonly used monomer in latex binder composition to have crosslinkable system since it has good chemical, physical properties and self-crosslinking ability. However, it emits formaldehyde to the environment during the handling and crosslinking reaction as a side product. Formaldehyde based resins also release formaldehyde by degradation or during condensation as a side product. Formaldehyde is known as a human carcinogen compound and is harmful to the human health and the environment. Therefore there is a general tendency to limit or completely eliminate formaldehyde based chemical goods. Previous studies performed in our research group involved the syntheses of novel formaldehyde-free crosslinkers that are free radically polymerizable and their incorporation into latex binders by incorporating them into the polymer chains. This manuscript focuses on the synthesis of new formaldehyde-free crosslinkers in the form of small molecules. New crosslinkers will contain cyclic acetals as functional groups and have tetra- or tri- functional analogues. They will be used to crosslink –NH2 and -OH containing polymer chains through trans-acetalization reactions, and their crosslinking ability at different temperatures will be investigated.
Investigation of reaction mechanism of epoxy resins with amide functional groups
Epoxy resins are used for many applications due to their noteworthy properties such as low creep, reasonable elevated temperature performance, chemical resistance and good adhesion to various substrate, etc. Epoxy resins gain such characteristics even at moderate level of crosslinking often referred as curings. There are various types of hardeners that initiate curing reaction, which all bring some characteristics to the material depending on their chemical and physical features. The information we have up to now, amides as hardener are not used as much as other kinds of curing agents like amines, anhydrides and acids, etc. Interestingly there are only a few reports on the reaction of epoxides with amides in general. Furthermore, in these limited studies done with amide and epoxy resins, there is little information about the effect of amide or the epoxide structure on these reactions, since the cured product analyses were mostly limited to FTIR analyses due to the solubility issues. Here, synthesis of soluble samples and their further spectroscopic analyses were aimed. Thus depending on these results about the structure of product, the idea about probable reaction pathway was developed. Also, temperature and heating time were adjusted to carry out the reaction under suitable conditions. Monomeric amide sources were used to avoid from complete crosslinked structure and provide solubility. Aromatic group containing amide and epoxy were used as well for comparison of effect of aromaticity and aliphaticity on reaction. In addition to FTIR and DSC, 1H-NMR and LS-MS analysis were realized for soluble samples.
Syntheses and characterization of polyesters derived from resorcinol and Iso/terephthaloyl chloride
Polyarylates are important class of polyesters, which are used for different application areas to improve thermal and mechanical properties of polymeric materials. They are also known as weatherable polymers that provide enhanced UV-protection. The different monomer compositions and their ratios in the polyesters affect the physical properties of polymers, such as flexibility or rigidity of polymer chains. On the other hand, linear and symmetrical monomer units make ordered packing while non-linear and non-symmetrical monomer units may produce cyclic oligomers. Therefore, they influence the glass transition temperatures (Tg) and the melting point (Tm) of the polymers. Previous studies performed in the literature involved the syntheses of polyarylates containing a composition of 1:1 ratio of 1,3 and 1,4 disubstituted acid chlorides. In this study, it was aimed to synthesize various polyesters with different ratios of these diacid chlorides to observe the structure-property relationship of the polymers. Furthermore, the syntheses of poly(ester-anhydrides) with the same monomers were performed to investigate the effect of anhydride linkages in the polymer backbone.
Effect of polymer topology on non-covalently bonded polyesters
Synthetic polymers have a crucial role in our daily lives. The irreversible nature of covalent bonding in conventional synthetic polymers makes them non-recyclable and prevents re-processing of the materials. Throughout the years with the development in technology, the demand for more advanced materials such as, reversible, recycable, and re-processable materials has increased. Supramolecular chemistry has emerged to solve this need for reversibility in polymer materials. Supramolecular polymers are more tunable and dynamic due to their non-covalent and reversible nature. Non-covalent interactions include metal-ligand coordinations, host-guest, π – π stacking, ionic interactions and hydrogen bonding. Ionic hydrogen bonding has the known characteristics of hydrogen bonding such as directionality, strength and versatility. For instance, a carboxylic acid and an amine give rise to ionic hydrogen bonding by acid-base complexation reaction. Thus, carboxyl-terminated polyesters, in principle, may coordinate with amines to produce supramolecular materials. In this study, the carboxyl-terminated polyesters and amines having different functionalities were mixed/reacted in a melt reactor to form acid-base coordinates. The thermal and mechanical properties of the amine treated polyesters were investigated through DSC and rheometric measurements, respectively.
Syntheses of polyesters and poly(ester-anhydrides) for industrial applications
Polyesters are one of the most important and widely used polymers in industry. Especially for powder coating application, the final properties of coating composition mainly depend on the polyester employed. These linear or branched polyesters are usually carboxylic acid terminated and thermally react with an epoxy hardener. The number of reactive end groups, the molecular weight, the viscosity, and the glass transition temperature (Tg) of polyesters affect the curing temperature and the levelling performance of the powder coating. For example, as the molecular weight of the polyester increases, Tg increases. This results in higher viscosity and thus poor levelling and surface quality. Therefore, in this study the aim was to synthesize poly(ester-anhydrides) that contains labile anhydride linkages. During the curing, those anhydride linkages will be broken and reacting with epoxy curing agents. In literature, poly(ester-anhydrides) are generally synthesized by acetic anhydride which limits its use in industry. In this study, aliphatic and aromatic cyclic anhydrides were examined for the synthesis of poly(ester-anhydrides) for industrial applications. They were melt mixed with carboxylic acid functional commercial polyesters that have different functionalities in order to investigate the effect of the total functionality on the poly(ester-anhydride) synthesis. Furthermore, a new polyester was synthesized and reacted with an aliphatic cyclic anhydride to gain know-how in polyesters and poly(ester-anhydride) syntheses. According to studies, the synthesis of poly(ester-anhydrides) with succinic anhydride (SA) seems more promising than pyromellitic dianhydride (PMDA) which has limited solubility. It is most likely that, high functionality of PMDA increased both the formation and scission of the targeted anhydride linkages.