Theses supervised by Prof. Dr. Yusuf Yağcı

İstanbul Technical University · Institute of Graduate Studies in Science

Photochemical routes to hyperbranched polymers

Light plays an important role in many processes in nature, such as atmospheric ozone production and photosynthesis. In the light-induced reactions, absorption of light generates excited state species that may take place in a number of different reactions such as isomerization, dissociation, abstraction, electron transfer and bond formation. Such light induced processes represent several advantages over conventional thermal techniques regarding the level of control since they can be accurately moderated in terms of wavelength, polarization direction and intensity, allowing spatial and temporal of the reactions. Light is used also in polymerization reactions following different mechanisms including radical, cationic, anionic and step-growth polymerization routes. In recent years, light induced processes are successfully employed also in controlled/living polymerization and click reactions for the formation of various complex macromolecular architectures. Hyperbranched polymers (HBPs), a unique class of dendritic macromolecules, have received continuous interest from macromolecular scientists due to their inherent properties such as high level of functional terminal units, high solubility and low viscosity. Despite enormous efforts devoted to the synthesis of HBPs by traditional methods, there are limited attempts to employ light induced processes. Until now, numerous strategies for the synthesis of HBPs have been reported. Depending on the number of monomers used in the polymerization, they can be classified in two categories; single-monomer methodology (SMM) and double-monomer methodology (DMM). SMM is the synthetic method that allows the syntheses of hyperbranched macromolecules by polymerization of only one type of monomers (ABn or latent ABn type). The SMM method covers various specific approaches: (a) polycondensation of ABn monomers; (b) self-condensing vinyl polymerization (SCVP); (c) self-condensing ring-opening polymerization (SCROP) and proton-transfer polymerization (PTP) and (d) chain-walking polymerization; and (e) dialkyne polycyclotrimerization. In 1995, Fréchet et. al. reported a new versatile synthetic strategy, SCVP which considers the polymerization of AB* type vinyl monomers. This strategy can also be defined as 'inimer route'. Inimers (AB*) are specific vinyl monomers consisting of pendant groups that can be converted into an initiating moiety by an external stimulus. In AB*structure, the A group serves as a vinyl moiety and the B* group signifies the initiating site. The chain initiation is realized through the addition of an initiating B* group to the double bond of another monomer. Hence, a dimer form comprised of two active sites B* and A* with one double bond is generated. The created dimer acts as an AB2 monomer, and lead to yield hyperbranched structure. This method fundamentally relies on the difference between the activities of chain propagation of the growth sites and the initiating sites. This behavior results a lower degree of branching (DB) in comparison to the DB of the HBP formed by polycondensation of AB2 monomers. The theoretical maximum DB of SCVP reaches 46.5%. The SCVP approach has been readily applicable to diverse type of controlled polymerization methods, such as living ionic, group transfer polymerization, ring opening and controlled radical polymerization (CRP) by suitably selected inimer structure variations. Taking account of the unique advantages of SCVP, we focused on the development of light induced processes for the synthesis of hyperbranched polymers with various architectures.In the first part of the thesis, a self-condensing vinyl polymerization for the preparation of hyperbranched polymers is explored on the basis of Type II photoinitiated system using benzophenone (BP) and camphorquinone (CQ) under UV and visible light. In this approach, 2-hydroxy ethyl methacrylate (HEMA) or 2-(dimethylamino)ethyl methacrylate (DMAEMA), and methyl methacrylate (MMA) were used as hydrogen donating inimers and comonomer, respectively.In the second part, branched polymers with different branching densities and their cross-linked analogues were synthesized by photoinduced self-condensing vinyl xxi polymerization (SCVP) via benzodioxinone photochemistry. Thus, MMA was copolymerized with two different comonomers, namely HEMA and DMAEMA in the presence bisbenzodioxinone (BBNZ) under UV light. Upon irradiation, BBNZ undergoes irreversible decomposition leading to the formation of benzophenone photosensitizer and bisketene. The released benzophenone is further photoexcited at the same wavelength to give the initiating radicals through hydrogen abstraction from the inimer. In the case of HEMA, additional branching sites were formed by the reaction of bisketen with the hydroxyl functionalities of HEMA.Finally, a novel photoinduced metal free ATRP approach was developed for the preparation of HBPs by SCVP. The approach relies on the copolymerization of MMA and styrene (S) with respective structurally antagonist inimers; 2-(2- bromoisobutryryloxy)ethyl methacrylate (BIBEM) and 4-vinylbenzylbromide (VBB) in the presence of perylene under visible light. In the process, excited state perylene directly reduces alkyl bromides to form carbon-centered radicals capable of iniaiting the polymerization of MMA and S, while BIBEM and VBB inimers contain both polymerizable vinyl moiety and bromide groups to generate branching points. As the halide groups remain at the chain ends, the methodology was shown to be a suitable candidate to form core-shell type block copolymers carrying hyperbranched and linear structures at the inner and outer spheres, respectively.

Cansu Aydoğan

İstanbul Technical University · Fen Bilimleri Enstitüsü

Counterion effect of amine salts on ring-opening polymerization of 1,3-benzoxazines

Polymers are advanced materials with a wide range of use in our daily lives, as a remarkable area where many researchers have been working. Recently, applications of polymers in science, technology and different areas of the industry and simple synthesis with the help of many different processes for these applications have highlighted the important features of the polymers. According to the changes by heat, polymers can be divided into two classes as thermoplastic and thermoset polymers. Thermoplastics are polymers which can be reshaped by heat. They have a wide range of uses depending on the structural differences such as poly(hexamethylene adipamide), poly(ethylene terephthalate), poly(vinyl chloride). As thermoplastics can be re-melted, they can also be used many times. Thermoset polymers can not re-melt because of their cross-linked structure. Due to these cross-linked structures, they are rigid and insoluble in solvents. Although there are types of phenolic resins such as phenol-formaldehyde, melamine-formaldehyde, and urea-formaldehyde, when looked the world-wide production schemes, phenol-formaldehyde resins appear to have a great importance. These phenolic resins, which are the first man-made thermoset plastics, are used in many areas, especially in the wood and wood industry, and are synthesized by the reaction of phenol, formaldehyde solutions. Although the traditional phenolics have excellent thermal and mechanical properties, there are disadvantages such as the formation of voids during vulcanization which prevents the formation of a void-free composite product. As since the first days of development of polybenzoxazines have eliminated almost all deficient due to their properties such as near-zero volumetric change upon curing, low water absorption, for some polybenzoxazines Tg much higher than cure temperature, high char yield, release of no toxic by-product during curing and no strong acid catalysts required for curing, they have became a good competitor against to traditional phenolic resins. When synthesized the first benzoxazine monomer by Holly and Cope in 1944, phenol, formaldehyde and primary amine groups used in the synthesis were varied and different benzoxazine monomers were developed. The polymerization of the benzoxazines is accomplished by heat, light and with catalysts. The polymerization occurs via ring opening reaction of the oxazine ring of benzoxazine. In addition to the many properties that make the benzoxazine structure in the polymer field superior to the classical resins and which are superior to the conventional resins, the high opening temperature (curing temperature) in the polymerization, which is one of the disadvantages of the industrial applications, requires new processes in production and increases the energy consumption significantly. Benzoxazines can be cured with acid catalysts at room temperature. However, the use of these catalysts is not preferred as it requires extra equipment and production scheme in terms of production. Many studies have been carried out based on the lower curing temperature benzoxazine synthesis due to the temperature sensitive side groups they have and the reducing of the curing temperature of the benzoxazines. In this thesis, the counterion effect of amine salts as catalyst has been investigated via the proposed mechanism for the purpose of reducing the high ROP of 1,3 classical benzoxazines. Aliphatic and aromatic different amine salts with Cl-, Br-, I-, NO-3 that provided the reduction on curing temperature for the synthesized P-a, P-Bn, B-a benzoxazine monomers was followed by DSC. In our results, it was observed that the amine salts decreased the ring-opening temperature and these decreases were interpreted according to the effect of the nucleophilic character of the counterion species of the amine and ammonium salts. As well as the nucleophilic character of counterions, the solubility and ionization of the amine salts in the melted benzoxazines have also been shown to play an important role on catalytic activity. The thermal properties of the cured polymers were analyzed by TGA. The latent (hidden) catalyst character of the amine salts was analyzed by using 1H NMR in solvent and at room temperature. This analysis showed that even after 24 hours the oxazine ring of benzoxazines was protected and the HX salts could be stored in the same container together with the benzoxazines in the long storage period. Accordingly, at the end of the study, it has been shown that the HX salts in the formulations can be used as strong and cost effective latent catalysts for the ring-opening polymerization of 1,3-benzoxazines.

Buket Akkuş

İstanbul Technical University · Fen Bilimleri Enstitüsü

Photoinduced step-growth polymerization of N-ethylcarbazole

Conjugated polymers have been an interesting research area due to their applicability in varied electronic and electrooptic devices. Organic photovoltaics, batteries, electrochomic devices, light emmiting diodes and sensors can be based on conjugated polymers, therefore there is a growing interest in this area. Some known strategies for the synthesis of these polymers are electropolymerization, oxidative polymerization, coupling reactions (e.g. Suzuki and Yamamoto). In 1862, polyaniline, which was the first conducting polymer, had been synthesized by Letheby, but features of this polymer were not totally understood, so it was not applied in industrial way. Then, polyacetylene, the first known conjugated polymer, was synthesized by Natta, in 1958. In the next decade, Hideki Shirakawa, accidently synthesized polyacetylene as silvery thin film, the conductivity of this film was much more conductive than previously synthesized polyacetylene. This was the milestone for these research area and made a great impact on researchers. Although polyacetylene has many superior characteristics, their applicability is restricted because of its structure can be disrupted easily when exposing water or oxygen in air. Therefore, this drawback leads the researches to create new stable conjugated polymers such as polythiophene, polypryrrole, polyphenylene and polycarbazole for overcoming these limitions. These polymers, which are synthesized with heterocyclic organic monomers, are used in the industrial applications. Though there are many methods for synthesizing the conjugated polymers, electrochemical and oxidative polymerization are frequently used. The conductivity of these polymers depend on the synthetic method, substances, doping agents and surface morphology. Photopolymerization; a general method of polymerization by photoinitiators and photosensitizers in which the reaction is initiated by the action of light, the functional monomers, oligomers and polymers being converted into higher molecular weight polymers. Photopolymerization is the most common method in terms of usage area and much faster than other polymerization methods, and therefore, leads to an economical and efficient process. According to the thermal polymerization methods, photopolymerization, which is an environmentally friendly method due to its low energy requirement, with high product yields and short reaction times. In the 21st century, photopolymerization has receieved prominence in the industrial sense and has been introduced in a wide range of the fields. In the industrial fields, photopolymerization method is used in the synthesis of adhesives, polishers, coatings, electronic device designs, tooth fillers, optical waveguides and paints. The photopolymerization method consists of four main stages. The photoinitiators interacts with the light in the "initiation" stage, using the energy from the light to initiate the reaction by interacting with the monomer. In the "growth" step, chain growth occurs using monomers. The chains that grow in the "chain transfer" phase continue their reactivity through a dehydrogenated molecule while the reactants terminate their hydrogen by removing hydrogen from other molecules present in the medium. In the "termination" stage, the reagents in the medium interact with each other and terminate the reaction by losing their activity. Although photopolymerization is studied under many headings, free radical and cationic photopolymerization are more widely used methods. There are two types of initiators in free radical photopolymerization: Type I, where the reaction begins with a single molecule, and Type II, including the photoinitiator as well as the coinitiator. Cationic photopolymerization can be examined under two main headings: direct and indirect photolysis. In this thesis, A noval method for photochemical step-growth systhesis of poly(N-ethylcarbazole) (PCE) via consecutive diphenyliodonium hexafluorophosphate (Ph2I+PF6-) mediated electron transfer and coupling reaction of the excited N-ethylcarbazole (EC) in the presence of Ph2I+PF6- as oxidizing salt proceeded efficiently giving EC radical cations. Subsequently, the protons released concomitantly with coupling of two EC radicals cantions. The successive reactions involving excitation, electron transfer, proton release, and coupling lead to the formation of PEC. The electrochemical properties and surface morphology of the thin films of the formed polymers before and after dedoping were investigated by cyclic voltammetry, differential pulse voltammetry, and atomic force microscopy techniques, respectively.

Erdem Sarı

İstanbul Technical University · Institute of Graduate Studies in Science

LED and visible light-induced metal free ATRP using reducible dyes in the presence of amines

Solar energy is the basis of all changes in nature. Most typical chemical reactions such as photosynthesis is sum of a series of step reactions using solar energy. Such naturally occuring reactions give inspiration to the chemists to apply photochemical strategies on varios chemical synthesis. Photochemical synthesis holds significant advantages over the traditional routes such as thermal and spatial control and low-energy requirements. More recently, the choice of sustainable, low-energy demanding processes compare to the conventional strategies become dominant which seems to be reasonable due to the changing financial and ecological patterns of the world. The year 2015 was declared to be the "International Year of Light" by UNESCO, emphasizing the indispensable quality of light in scientific, cultural, medical and social platforms. Applications of the light energy to the polimer science spread to a broad scale resulting in an increasing number and quality of the efforts on the topic. However, the development and utilization of environmentally friendly, reusable and low-energy using light-induced processes is still below satisfactory levels from the point of view of both academic and industrial demands. In addition, synthesis of macromolecular structures with well-defined structures and functional groups, and controlled molecular weights has become an important research field for polymer scientists. Among the controlled radical polimerization methods, atom transfer radical polymerization (ATRP) is the most-widely used method as it has high tolerance towards many functional groups present in the initiator and monomer structure and is applicable to a wide range of monomers. The major drawback associated with the ATRP process is the requirement of the low oxidation state copper halide catalytsts, which are hard to remove from the polymers obtained. The residual inorganic materials in these polymers prevent the application of these materials espacially in bioapplications. In addition, these are thermal processes and application of photochemical strategies to overcome these advantages are insufficient. Thus, additional innovative research is required due to the insufficiency of adaptation of light into the present technologies and the existence of drawbacks in the proposed strategies. In the preparation of macromolecular structures, linear polymer and network structured polymers, based on epoxy systems, synthesis deserve special attention. In this respect, photochemical methodologies are widely used as they provide low-energy requirements and simpler experimentation procedures. Recently, it has been demonstrated that some controlled polymerization techniques can be performed in the absence of inorganic catalysts by the help of light energy. Moreover, it has been also shown that the industrially applied epoxy curing can be achieved by photochemical procedures. Limited number of the existing technologies in this field proves that the topic is open to new developments and innovations. A new photoinitiating system involving electron acceptor dyes, namely eosin Y and erythrosin B in conjunction with alkyl halides and amines for photo-induced ATRP of (meth)acrylates and vinyl monomers in the absence of inorganic catalysts is reported. The polymerizations could be efficiently activated by the photomediated redox processes producing polymers with controlled chain end functionality and narrow molecular weight distribution. The dye/amine system was shown to be efficient under various colors of LED and industrially available visible light irradiation. The livingness nature of the polymerization was proved by GC analyses and the irradiation dependency of polymerization was confirmed by light on/off experiments.

Ceren Kütahya

2016

Functional polymersPhotoactivityCopolymers+1

Functional high performance polybenzoxazines and their properties

Phenolic resins are leading the polymer market due to their widespread applications such as adhesives, structural applications materials in aerospace, printed circuit boards, conductive polymer elements, and encapsulation materials for electronic applications. Phenolic resins, acrylates, bismaleimides, polyesters, epoxy resins and isocyanate polymers are the best known members of the thermosets. High processing temperatures and void formation during curing are the main challenges must be overcome regarding application of these materials. Lately, benzoxazine based phenolic resins has been developed and attracted significant attention as a novel type of phenolic resin. Polybenzoxazines have various outstanding properties, including good thermal stability, high glass transition temperature, high char yield, no need of catalysts for curing, near-zero volume changes during curing, low moisture absorption and no volatile release. Recently, owing to the design flexibility of benzoxazine and related polymeric benzoxazine precursors, various smart materials were synthesized by innovative strategies including self-healing materials, electrochemically activated smart coatings, smart sorbents for heavy metals, hydrophobic surface applications and porous polybenzoxazine resins. Taking account of the unique advantages of these strategies and attractive characteristics of polybenzoxazines, in this thesis, we focused on the combination of various functional groups with benzoxazine precursors and then investigated the resulted products properties. In the first part of the thesis, a self-healing strategy for poly(propylene oxide)s bearing benzoxazine units (PPO-Benz) through supramolecular attractions is described. Poly(propylene oxide) bisamine (PPO) with a molecular wieght of 2000 Da were reacted with formaldehyde and bisphenol A to yield desired PPO-Benz with 12360 Da. The cross-linked polymer films were then prepared by solvent casting of suitable compositions of PPO-Benz and carboxlic acid containing benzoxazine monomer (Carb-Benz) in chloroform followed by thermal ring opening reaction of benzoxazine groups at 200 °C. Thermal curing and thermal stability of the film and final products were investigated. It was demonstrated that the self-healing capacity of the films were improved by employing Carb-Benz in the formulation. Figure 1 : Self-healable film preparation from carboxylic acid containing benzoxazine monomer and PPO-Benz. In the second part of the thesis, a novel strategy to obtain sulfur rich polybenzoxazine copolymers by reacting allyl functional benzoxazine (BA-ala) and elemental sulfur was described. Simultaneous inverse vulcanization and ring-opening reactions of benzoxazine generated soluble copolymers in specific feed ratios. Parameters such as monomer structure and feed ratios on the polymerization were studied. The thermal stability of the copolymers was investigated and compared to that of polybenzoxazines derived from neat BA-ala by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The surface properties of the materials as examined by scanning electron microscope (SEM) confirmed that elemental sulfur and benzoxazine copolymers can be produced without a phase separation at micrometer level. Moreover, a sponge like insoluble macroporous polybenzoxazine networks was obtained at the 20%-wt feed ratio of sulfur. Figure 2 : A novel strategy to obtain sulfur rich polybenzoxazine copolymers by reacting allyl functional benzoxazine (BA-ala) and elemental sulfur. Finally, side-chain benzoxazine functional polybutadienes was synthesized by photoinduced hydrogen abstraction process. First, photosensitive benzoxazine compounds possessing both chromophoric carbonyl and hydrogen donating sites in the structure were synthesized using vanillin or 4-hydroxybenzophenone in the conventional benzoxazine synthesis. Irradiation of neat polybutadiene (PB) in the presence of the corresponding benzoxazines, namely benzophenone benzoxazine (BPh-ptol) and vanillin benzoxazine (Van-a) under 300–350 nm light gave PBs with approximately 4-5 benzoxazine units per chain. Successful modification was confirmed by the spectral and thermal investigations. It is shown that benzoxazine modified PBs undergo thermally activated curing in the absence of any catalyst forming polybutadiene thermoset with high char yield. Figure 3 : Photoactive benzoxazines having both chromophoric carbonyl and hydrogen donating sites were synthesized using vanillin or 4-hydroxybenzophenone by conventional benzoxazine synthesis methodology.

Mustafa Arslan

İstanbul Technical University · Fen Bilimleri Enstitüsü

2016

İstanbul Technical University · Institute of Graduate Studies in Science

Photoinitiated metal-free controlled/living radical polymerization using polynuclear aromatic hydrocarbons

Recently, photoinitiated polymerization has received revitalized interest as it congregates a wide range of economic and ecological anticipations. Because of the excellent advantages, photoinduced polymerization has widely been applied in coatings, adhesives, inks, printing plates, optical waveguides and microelectronics. Theadvantegesofthismethodarehighrateofpolymerizationatambienttemperatures, low energy consumption, solvent-free polymerization, spatial and temporal control over the processes. There currently exist a few methods, where photo induced polymerization can be applied including controlled/living radical polymerizations such as iniferter, nitroxide mediated radical polymerization(NMRP), reversible addition-fragmentation chain transfer polymerizations (RAFT) and atom transfer radical polymerization (ATRP). Among them, ATRP became the most commonly used method as it has higher range of tolerance not only to the initiators but also to various number of monomers. Traditional ATRP requires a low-oxidation state transition metal complex (commonly CuX/L, X = Cl or Br and L = ligand) in conjunction with an appropriate alkyl halide (R-X). The photochemical initiation both enables the easy control of the polymerization under ambient temperature even for heat-sensitive monomers and tends to minimize side reactions like chain transfer or depolymerization. In this thesis, photo-initiated metal-free controlled living radical polymerization of (meth)acrylates, and vinyl monomers was investigated using the polynuclear aromatic compounds,pyreneandanthracene. Fluorescencespectralanalysesalongwithnuclear magneticresonancestudieswereperformedtodeterminetherateconstantsofinitiator radical formation and investigate the mechanisms of polymerization. The obtained polymers were analyzed by spectral and chromatographic methods. Results show that the excited state anthracene undergoes a faster electron transfer reaction with the alkyl halide initiator than the excited state of pyrene. Pyrene excimers, which are formed at higher concentrations, also react with alkyl halides to form initiator radicals. Although pyrene monomers and excimers are acting slower, polymers with higher control over the chain end functionalities and molecular weight characteristics are obtained in comparison to anthracene as sensitizer.

Andrıt Allushı

2016

İstanbul Technical University · Fen Bilimleri Enstitüsü

Mn2(CO)10 based visible-light photo initiating systems for distinct macromolecular structures

Light is a particularly fascinating stimulus because it can be precisely modulated in terms of wavelength, polarization direction and intensity, allowing spatial and temporal of the chemical reactions. Photochemical reactions involve the absorption of light to create an excited species that may undergo a number of different reactions such as dissociation, isomerization, abstraction, electron or energy transfer, and bond formation. These reactions have been studied quite extensively in various fields including organic chemistry, molecular biology and electronics etc. Photoinduced chemical reactions can advantageously be utilized in the field of polymer chemistry. Among them, photoinitiated polymerization which is a process that transforms monomers into polymers under light irradiation, has many advantages over other polymerization methods. It is fast, uses little energy, and readily occurs at room temperature. It has been estimated that energy costs can be reduced 30% by switching from thermal polymerization to photoinitiated polymerization. Therefore, it has been the basis of numerous conventional applications in surface coatings, printing inks, adhesives, microelectronics, printing plates and three dimensional imaging and micro-fabrication processes. Additionally, there is a huge number of photoinitiators for such photo-induced systems. Among them, dimanganese decacarbonyl (Mn2(CO)10) in conjunction with organic halides appears as an ideal photoinitiating system for the preparation of polymers with various topologies. Additional attractive features of the transition metal carbonyl compound include efficient light absorption in the visible region and solubility in a wide variety of reactive monomers. Many different applications of Mn2(CO)10 chemistry including initiation of free radical polymerization, promotion of cationic polymerization, mechanistic transformation, graft copolymerization, iodine degenerative transfer polymerization, preparation of telechelics and hyperbranched polymers have been reported and reviewed. Taking account of the unique advantages of Mn2(CO)10 photochemistry, in this thesis, we focused on the development of new Mn2(CO)10 based photochemical approaches for the synthesis of macromolecular structures with various architectures. In the first part of the thesis, polyolefin graft copolymers were prepared by combining ring-opening metathesis polymerization (ROMP), hydrobromination, and visible light-induced free radical polymerization. First, cis-cyclooctene (COE) was polymerized via ROMP in the presence of a chain transfer agent and quantitatively hydrobrominated to give bromo functional polyethylene (PE-Br). Subsequent irradiation of PE-Br in the visible range using dimanganese decacarbonyl (Mn2(CO)10) initiated free radical polymerization of tert-butyl acrylate (tBA) resulting in the formation of polyethylene-graft-poly(tert-butylacrylate) (PE-g-PtBA). The effect of Mn2(CO)10 concentration and irradiation time on the grafting density and efficiency was evaluated. Then, the tBA moieties of PE-g-PtBA were hydrolyzed into acrylic acid functionalities by acidolysis to obtain hydrophilic polyethylene-graft-poly(acrylic acid) (PE-g-PAA). In the second part, a new photoredox catalyst system for Atom Transfer Radical Polymerization (ATRP) is developed on the basis of visible light photocatalysis using Mn2(CO)10 that initiates and controls the polymerization at ambient temperature. The polymerization was performed by Mn2(CO)10/alkyl halide system with visible- or sunlight in the presence of parts per million (ppm) copper catalysts. The photogenerated •Mn(CO)5 radicals are not only able to abstract halogen atoms from alkyl halides to generate carbon centered radicals but also reduce the copper(II) bromide (CuIIBr2) to copper(I) bromide (CuIBr) directly, which was used as activator in the ATRP of vinyl monomers such as methyl methacrylate, methyl acrylate and styrene. The method was also used to synthesize graft copolymers from commercially available poly(vinyl chloride) without additional modification. Finally, a new photoinitiating system for living cationic polymerization of vinyl ethers is reported. In the current approach, visible-light irradiation of Mn2(CO)10 in the presence of an alkyl bromide results in the formation of carbon-centered radicals. The photochemically generated radicals were then oxidized by diphenyliodonium ions to the corresponding cations. These cations can add vinyl ether monomers, which are then rapidly deactivated by the bromide anions to give α-halide functional end groups. Poly(vinyl ether) chains are then grown through successive photoinduced radical oxidation/addition/deactivation (PROAD) in a controlled manner. The living nature of the system is evaluated through kinetics studies and block copolymer formation.

Mustafa Çiftçi

2017

Atom transfer radical polymerizationGraft copolymersElectrochemical polymerization+7

Poli(Fenilen vinilen) türevlerinin görünür bölgede katyonik polimerizasyon için fotobaşlatıcı olarak kullanımı

Conjugated polymers have been widely studied as materials due to their interesting optical and nonlinear optical properties and electronic conductivity that lead to a wide range of practical applications such as information storage, optical signal processing, substitutes for batteries, solar energy conversion, and optical signal processing. Moreover, electroluminescence from conjugated polymers is a rapidly increasing a great deal of research has gone into research interest since the first report of polymeric lightemitting diodes (PLEDs) based on poly(phenylene vinylene) (PPVs). Current interest in among a variety of conjugated polymers, In particular, PPV and its derivatives have attracted much attention for the most promising class of high performance polymers due to their relatively high photoluminescence (PL) and electroluminescence (EL) quantum efficiencies as well as good colour tunability through molecular structure designs. They also show high chemical and excellent mechanical properties, thermal stability that allows the fabrication of electronic devices such as flexible LEDs. PPV itself has a rigid structure and is inherently insoluble, thus making it impossible to process these materials into thin films required for the most applications. As a result, considerable effort has been directed toward the preparation of well-defined conjugated polymers with improved solubility, processability and stability. Incorporation of conformationally mobile, relatively long and flexible side chains onto the polymer backbone has been important for synthesizing fusible and soluble rigid-rod conjugated polymers. Taking into consideration the substantial interest not only in the synthesis of new types of polymers, but also in the modification of commodity polymers to improve their properties to meet the requirements for high-tech applications, with a soft coil polystyrene (PSt) or poly(ε-caprolactone) (PCL) has been used in which nanostructured photoactive conjugated oligo(phenylene vinylene) segments are attached as side chains to the backbone. It is possible to form a new polymer with novel and interesting properties. Utilization of several conjugated aromatic compounds for the sensitization of onium salts has prompted us to apply PPVs as photosensitizers for cationic polymerization. Therefore, in order to overcome solubility problems of bare PPVs associated with the rigid structure, PPVs with polystyrene and poly(ε-caprolactone) grafts (PPV-g-PSt and PPV-g-PCL, respectively) were synthesized. The first step in the synthesis of the desired PPVs was to obtain precursor macromonomers. In the preparation of macromonomers, controlled polymerization methods were delibaretly employed so as to obtain polymers with desired functionalities at the chain ends, and combine with proper molecular weights and polydispersities Dibromo-benzene functional polystyrene (DBB-PSt) was synthesized by Atom Transfer Radical Polymerization (ATRP) of styrene by using 1,4-dibromo-2-(bromomethyl)benzene as initiator in the presence of CuBr/bpy as catalytic system. The corresponding poly(ε-caprolactone) derivative (DBB-PCL) was prepared by Ring Opening Polymerization (ROP) of ε-caprolactone by using [2,5-dibromo-(4-hydroxymethyl) phenyl)]methanol as bifunctional initiator, in the presence of stannous octoate. In the next step, these polymers were coupled with (4-formylphenyl)boronic acid by Suzuki coupling to give aldehyde functional macromonomers. Finally, the obtained polymers were coupled with p-xylylenebis(triphenylphosphonium bromide) by the Wittig reaction in the presence of potassium tert-botoxide to yield the desired conjugated polymers. The resulting main chain conjugated graft copolymers were soluble as were the starting macromonomers and PPVs showed blue or green fluorescence in solution. Even tough photopolymerization can be initiated radically, cationically and anionically, much effort has been devoted to free radical and cationic systems mainly due to the availability of a wide range of photoinitiators and the great reactivity of monomers. The majority of industrial applications of photoinitiated polymerizations for various techniques deal with free-radical systems. However, there are some drawbacks associated with this type polymerization such as the inhibition effect of oxygen and post-cure limitations which may affect the properties of the final product. Therefore, photinitiated cationic polymerization holds considerable promises in the future, particularly as a means of overcoming these limitations. Some important examples of these initiators are iodonium and sulfonium salts. These onium salts give an irreversible photochemical reaction in response to UV excitation due to their thermal stability, solubility in monomers and efficiency in generating reactive species. However, these onium salts only absorb in the region of 220–300 nm. This means, in visible region, they are either poorly responsive or completely insufficent. Thus, their use in applications requiring long wavelength light emitting sources is limited. This drawback can be evaded by using an activator that broadens the spectral sensitivity of the onium salt photoinitiators. These activators are photosensitizers and they can initiate polymerization in the near-UV or visible wavelengths of light. In this work, we report the use of PPVs derivatives for electron transfer photosensitization of onium salts. For this purpose, PPV-g-PSt and/or PPV-g-PCL were used as photosensitizers. The excited state emission characteristics of the compounds were investigated by means of fluorescence and phosphorescence spectroscopic measurements. The cationic polymerization of typical monomers, such as cyclohexene oxide (CHO), isobutyl vinyl ether (IBVE) and N-vinylcarbazole (NVC) with the described initiating system was also tested at room temperature at appropriate wavelengths in the presence of oxidizing salts such as diphenyliodonium hexafluorophosphate (DPI), and N-ethoxy-2-methylpyridinium (EMP). The initiation mechanism, as correlated with optical absorption and fluorescence spectroscopic measurements, free energy changes (ΔG) and proton scavenging studies, involves formation of exciplex by the absorption of light in the first step. Subsequently, an electron transfer from the excited PPV-g-PSt or PPV-g-PCL to oxidizing salt occurs to yield radical cations of the PPV backbone. Thus, formed radical cations abstract hydrogen from the surrounding monomer or the solvent to release a Bronsted acid, which initiates the polymerization. Triphenylsulphonium hexafluoroarsenate (TPS) was found to be inefficient in the photoinduced electron transfer process due to the unfavorable thermodynamic conditions.

Semih Erdur

İstanbul Technical University · Institute of Graduate Studies in Science

Activated clayAtom transfer radical polymerizationComposite polymers+4

Polimer/kil nanokompozitlerin hazırlanmasında yeni yöntemler

Polymer/clay nanocomposites have exhibited immensely enhanced properties and higher performance as compared to both their conventional polymer composites and pure polymers. Currently polymer/clay nanocomposites can be prepared by three ways such as solution mixing, melt blending, and in-situ polymerization. Solution mixing method consists to solubilize polymer in an organic solvent, then the clay is dispersed in the obtained solution and subsequently either the solvent is evaporated or the polymer precipitated. The large quantities of volatile solvent necessary for this approach make it less attractive as an industrial process. Melt blending is a solvent-free method to enable mixing of the layered silicate with the polymer matrix in the molten state. However, very careful attention has to be paid to finely tune the processing conditions to increase the compatibility of clay layer surfaces with the polymer matrix. In the in-situ polymerization technique, the monomer, together with the initiator and/or catalyst, is intercalated within the silicate layers and the polymerization is initiated by external stimulation such as thermal, photochemical or chemical activation. The chain growth in the clay galleries triggers the clay exfoliation and hence the nanocomposite formation.The in-situ polymerization can be initiated by externally stimulation such as thermal, photochemical or chemical activation. The growth of polymer chains within the clay galleries may lead to the clay exfoliation and hence the nanocomposite formation.Recently, a highly efficient method, namely copper (I) catalyzed azide/alkyne cycloaddition (CuAAC) "click" reaction, in which exfoliation is rooted in the functional groups of the intercalant that readily react with the antagonist groups of the preformed polymershas been established. To take advantage of click chemistry, azide and alkyne partners could each be incorporated in either the clay surface or polymer chain. The quantitative efficiency of coupling reaction coupled with tolerance to a wide variety of functional groups and reaction conditions make this coupling process highly attractive for the nanocomposite preparation. However, there are limited examples in the literature to date regarding the preparation of polymer/clay nanocomposites via the CuAAC click reactions. In the first part of thesis,an efficient protocol, atom transfer radical nitroxide coupling chemistry (ATNRC), for the preparation of polymer/clay nanocomposites via grafting-onto strategy with well-defined polymer synthesized via atom transfer radical polymerization has been described. The highly efficient ATNRC chemistry was based on mixing a nitroxide-containing organoclay with corresponding halide-containing polystyrene in the presence of Cu(I)Cl/PMDETA catalytic system was developed.The radical coupling, taking place between the clay layers, not only leads to attach the polymer chain but also successful nanocomposite formation with highly exfoliated morphology. Spectroscopic and microscopic investigations revealed that successful nanocomposite formation has been achieved by this method. By addition of small amounts of layered silicate loadings resulted in remarkable improvements of thermal properties of nanocomposites. In the second part of thesis,a series of A3-type star poly(methylmethacrylate)/clay nanocomposites has been prepared by in-situ atom transfer radical polymerization (ATRP) initiated from organomodified montmorillonite containing quaternary trifunctional ATRP initiator. The first order kinetic plot showed a linear behavior, indicating the controlled character of the polymerization. The resulting nanocomposites were characterized by spectroscopic, thermal and microscopic analyses. Spectroscopic and microscopic investigations revealed a complex morphology, with partial intercalation/exfoliation, which depends on the concentration of clay.The exfoliated nanocomposite was obtained when polymerization was conducted with 1% of organic clay loading.However, with increasing the clay loading to 3, 6 and 10%, the degree of exfoliation of the nanocomposites decreased, which confirmed by both spectroscopic and microscopic analyses. Thermal analyses show that all nanocomposites had higher glass transition values and thermal stabilities compared to neat polymer. In the third part of thesis, the preparation of polymer/clay nanocomposites by specific hydrogen bonding interactions between surface functionalized silica nanoclays and 2-ureido-4[1H]pyrimidinone-bonded supramolecular poly(ethylene glycol) or poly(ɛ-caprolactone)s, which has self-association capability through quadruple hydrogen bonds was described. An 2-ureido-4[1H]pyrimidinone (UPy) motif with self-association capability (through quadruple hydrogen bonds) was successfully anchored onto montmorillonite clay layers. Polymer/clay nanocomposites were prepared by specific hydrogen bonding interactions between surface functionalized silica nanoclays and UPy-bonded supramolecular poly(ethylene glycol) or poly(ɛ-caprolactone). The mixed morphologies including intercalated layers with a non-uniform separation and exfoliated single layers isolated from any stack were determined by combined spectroscopic and microscopic analyeses. Thermal measurements showed that all nanocomposites have higher decomposition temperatures and thermal stabilities comparedto neat polymer. Thedifferential scanning calorimetry data implied that thecrystallinity of polymers did not show essential changes upon introduction of organomodified UPy clays.

Muhammed Aydın

İstanbul Technical University · Fen Bilimleri Enstitüsü

İstanbul Technical University · Institute of Graduate Studies in Science

Organik ve sulu ortamlarda serbest radikal polimerizasyonu için tek bileşenli tip II fotobaşlatıcı olarak poli(vinil alkol)-tiyoksanton

In recent years, photoinitiated polymerization has received revitalized interest as it congregates a wide range of economic and ecological anticipations. The most important elements of photoinitiated polymerization are the photoinitiators, which absorps the light to yield the species responsible for the initiation of polymerization. Thus, development of new photoinitiating systems became an important subject for the synthetic researchers in the past few years. Both free radical and cationic photoinitiators are intensively examined and their initiating mechanisms are examined in detail. Free radical photoinitiators can be divided into Type I (α or less common β cleavage) and Type II (H-abstraction). Some of the most influential Type I initiators are benzoin ether derivaties, benzil katals, hydroxylalkylphenones, a-aminoketones and acylphosphine oxides. Besides that typical Type II photoinitiators include aromatic carbonyl ssuch as benzophenone and derivatives thioxanthone (TX), benzil, quinones, and organic dyes, however alcohols, ethers, amines, and thiols are used as hydrogen donors. Type II photoinitiators are the most widely used in many technologically important UV curing applications because of their excellent light absorption characteristics. The radicals formed on the thioxanthone moiety do not actually participate in the initiation process on account of the steric hindrance and delocalization of the single electron on the π-system. Although they exhibit excellent initiation efficiency, the hydrogen donor compounds at high concentrations, have several intrinsic disadvantages such as offensive odor, toxicity, and migration in UV-curing technology. Several strategies have been developed to overcome these problems. The usual approach is to chemically incorporate the hydrogen-donating sites into TX chromophores. In this current work, TX moiety was incoperated to the side chains of commercially available poly(vinyl alcohol) (PVA) by a simple acetalization reaction. Initially, the designed thioxanthone structure with aldehyde functionality (TX-A) was facilely synthesized. Afterwards, the obtained TX-A was linked to the PVA counterpart by a simple addition reaction to yield the desired PVA-TX macroinitiator. PVA-TX polymeric photoinitiator exhibits typical TX absorption characteristics and soluble in water and some polar organic solvents such as DMF and DMSO. Moreover, PVA-TX displays one-component nature and initiates the polymerization in both organic and aqueous media without the necessity of additional hydrogen donor donor due to the presence of remaining hydrogen donating hydroxyl groups in the structure.

Senem Körk

BiopolymersConducting copolymers

Fonksiyonel konjuge polimerler

The considerable role of conjugated polymers (CPs) in emerging synthetic bio-applications, optical, electronic, diodes, and display technologies, represents the promising way in which considerable endeavors have been directed towards the realization of many aspects of conducting organic polymers. Conducting polymers are known as "synthetic metals", making them fundamental materials in many research fields because of their outstanding characteristics. They exhibit both excellent conductivity and high mechanical strengths and processability. The use of CPs as an excellent immobilization platform for biomolecules led to the development of efficient biosensors, which were easy to process, had the ability to conduct electricity at any desired level, had a low cost, and straightforward preparation techniques. CPs provide high surface area, adjustable morphology by arranging the thickness of the polymer film and offer extensive stability of the enzymes incorporated in them. Furthermore, these materials also facilitate structural and electronic modifications which can be used in detecting a target compound in any test solution. The polymer structure can be tuned to accomplish the desired properties, producing a sensitive and reproducible microenvironment for biological reactions to mimic the naturally occurring environments of the biological molecules. Among vast number of CPs, poly(p-pheneylene)s (PPP)s and polythiophenes (PT)s are the most promising class of polymer in terms of relatively high photoluminescence, electroluminescence quantum efficiencies and thermoxidative stability and so on. Conjugated structure of CPs can create excellent one-dimensional surface for energy transport of electrons and strong UV absorption. Especially, their fluorescence feature is one of the most susceptible to environmental change and this allows for eminent selectivity in signaling reporter group materials and provides advantages for CPs to be used in sensor technologies including pH sensors, temperature sensors and recently developed biosensors. Recent innovative strategies for the syntheses of functional polymeric structures bearing polypeptides, amino-rich and water soluble groups have received enormous interest in the fields of biomedicine, drug delivery, biomineralization, bioconjugations, and tissue engineering. Taking account of the unique advantages of these strategies, in this thesis, we focused on the combination of PPPs and PTs with polypeptide, amino and water soluble groups in the same conjugated backbone. In the first part of thesis, a simple and efficient approach for the electrochemical deposition of polypeptides as bio-based covering materials for surface design is described. The method involves N-carboxyanhydride (NCA) ring-opening polymerization from its precursor to form a thiophene-functionalized polypeptide macromonomer (T-Pala), followed by electropolymerization. The obtained conducting polymer, namely polythiophene-g- polyalanine (PT-Pala), was characterized and utilized as a matrix for biomolecule attachment. The biosensing applicability of PT-Pala was also investigated by using glucose oxidase (GOx) as a model enzyme to detect glucose. The designed biosensor showed a very good linearity for 0.01–1.0 mM glucose. Finally, the antimicrobial activities of newly synthesized T-Pala and PT-Pala were also evaluated by using the disc diffusion method. In the second part of thesis, we report a novel approach for fabrication of multifunctional conjugated polymers, namely poly(p-phenylene)s (PPPs) possessing polypeptide (poly-L-lysine, PLL) and hydrophilic poly(ethylene glycol) (PEG) side chains. The approach is comprised of the combination of Suzuki coupling and in situ N-carboxyanhydride (NCA) ring-opening polymerization (ROP) processes. First, polypeptide macromonomer was prepared by ROP of the corresponding NCA precursor using (2,5-dibromophenyl) methanamine as an initiator. Suzuki coupling reaction of the obtained polypeptide and PEG macromonomers both having dibromobenzene end functionality using 1,4-benzenediboronic acid as the coupling partner in the presence of palladium catalyst gave the desired polymer. A different sequence of the same procedure was also employed to yield polymer with essentially identical structure. In the reverse sequence mode, low molar mass monomer (2,5-dibromophenyl)methanamine, and PEG macromonomer were coupled with 1,4- benzenediboronic acid in a similar way followed by ROP of the L-Lysine NCA precursor through the primary amino groups of the resulting polyphenylene. In the third part of thesis, a novel approach for bioconjugation associated with a fluorescent conjugated polymer is demonstrated. For this purpose, a conjugated polymer, poly(p-phenylene) (PPP), with lateral substituents, namely primary amino groups and poly(ethylene glycol) (PEG) chains, as a potential building block for polymer bioconjugates was synthesized and characterized. The synthesis was achieved through Suzuki polycondensation reaction in the presence of Pd(PPh3)4 catalyst by using independently prepared PEG and amino functionalized dibromo benzenes in conjunction with benzene diboronic acid. For the evaluation of the bioactive PPP labeled with folic acid (FA) as a potential targeted cell imaging probe, HeLa and A549 cancer cells were used. Cytotoxicity assay showed that the polymer was not toxic to either of the cells. Additionally, the fluorescence images showed that, depending on the level of the FA receptors on the cell surfaces, the fluorescent intensity in HeLa cells was obviously higher than A549 cells when treated with FA conjugated PPP-NH2-g-PEG polymer. The resulting FA/PPP-NH2-g-PEG conjugate was successfully used as a bioconjugate for targeting and specifically imaging FA receptor positive HeLa human cervical cancer cells. Summary, we successfully achieved the systhesis, characterization and some bioapplications of complex macromolecular architecture based on conjugated polymers bearing polypeptide, water soluble pendant ,PEG, and primary amine groups. The systhesis of polypeptide squences were achieved by NCA-ROP technique based on transformation of α-amino acids to urethane derivatives which have possibility to obtain polypeptides in the well-designed and desicive control of molecular weight with one spot intra-molecular cyclization reaction in the presence of primary amino functional initiators. We succesfully used the primary amino functional thiophene and phenyl compounds as NCA-ROP initiator to obtain macromonomers having electropolymerization ability and possibility to give Suzuki coupling polymerization. After the obtaining of conjugated polymers bearing polypeptide and primary amine groups based on PPP and PTs, some biofunctional material was used in the step of bioapplications.

Hüseyin Akbulut

İstanbul Technical University · Institute of Graduate Studies in Science

Atom transfer radical polymerizationBlock polymersPhotoactivity+6

Makromoleküler sentezler için fotokimyasal yöntemler

Photo-induced reactions have been receiving a revitalized interest as it congregates a wide range of academical, commercial, economical and ecological anticipations. In the area of synthetic polymer chemistry, most of the research intensively focused on photopolymerizations, which is typically the process that transforms a monomer into a polymer by the help of the incident photon energy. Even when monomers are exposed to light of appropriate frequencies, polymers can be obtained. However such reactions are generally low-yielded reactions and almost always an additive is required to increase the efficiency. This additive is known as a photoinitiator which absorbs the light and decomposes to give the reactive species which are responsible for initiation of polymerization. Both free radical and cationic polymerizations are known and their mechanisms were investigated in detail. Both polymerization mechanisms have its own advantages and the researchers are generally interested in the development of new photoinitiating systems for both polymerizations. The reason behind the research for such developments lies on the fact that no photoinitiating system can be perfectly applied to all industrial applications. There has been tremendous effort to develop photoinitiators with enhanced absorption characteristics, solubility, low odor, low migration, and non-yellowing properties. Specifically, the development of photoinitiators absorbing light in the near UV-visible light range of the electromagnetic spectra is a key challenge in the last decade due to the fulfillment of green chemistry demands. Utilization of photochemistry to the synthetic polymer chemistry is not only based upon the photopolymerization methodologies, but also the use of photon energy for the triggering of various reactions. In such processes, the photo-inductions provide spatial and thermal control over the processes under mild conditions compare to the thermal modes. Recently, numbers of papers reported the use of photochemistry to induce the very well-known atom transfer radical polymerization and click chemistry reactions. Both processes require first oxidation state copper salts (CuCl or CuBr) and by photochemical reductions, it was demonstrated that one can generate Cu(I) starting from Cu(II) salts by using various photoinitiators. Thus, the necessity of preserving easily oxidizable Cu(I) species by cumbersome reaction conditions (i.e. inert atmosphere requirements, freeze-thaw pump cycles etc.) can be eliminated as a result of the stability of Cu(II) salts. In this thesis, three different publications are presented, which are mainly based on the photo-induced processes for macromolecular syntheses. In the first part, the synthesis, characterization and initiation efficiency of a novel polymeric Type II photoinitiator, namely poly(ethylene oxide) dimethylammonium thioxanthonemethyl-carboxylate (PEO-NH+(CH3)2 TX-CH2COO-) possessing both photochromophoric and hydrogen donating groups in the structure is demonstrated. In contrast to existing Type II photoinitiators, the present photoinitiator initiates free radical polymerization by counter anion excitation even in the absence of added hydrogen donors. The photoinitiator can be applied to the polymerization of monomers soluble in organic solvents or water. Thus both hydrophobic and hydrophilic polymers can be easily obtained using this photoinitiator developed. In the second part of the thesis, a novel visible light sensitive photoinitiating system for the cationic polymerization of typical monomers, e.g. of oxiranes such as cyclohexene oxide, vinyl ethers such as iso-butyl vinyl ether, and other vinyl monomers such as N-vinylcarbazole, using fullerene derivatives is described. The cationic polymerization of these monomers was initiated at room temperature upon irradiation in the visible region (λinc > 400 nm) in bulk or chlorobenzene solutions with polystyrene-C60 (PS-C60) adduct or bare C60, respectively in the presence of oxidizing salts such as silver hexafluorophosphate (AgPF6) and diphenyliodonium hexafluorophosphate (Ph2I+PF6-). A feasible mechanism, as correlated with optical absorption measurements, free energy changes (ΔG), and proton scavenging studies, involves formation of exciplex by the absorption of light in the first step. Subsequent electron transfer from excited C60 or PS-C60 to oxidizing salt yields radical cations of the fullerene derivatives. Both radical cations and strong Bronsted acid derived by hydrogen abstraction initiate the cationic polymerization of variety of monomers. Finally, development of a long wavelength photoinduced "Copper (I) Catalyzed Azide-Alkyne Cycloaddition (CuAAC)" click reaction based on the electron transfer reactions of excited states of polynuclear aromatic compounds such as anthracene, pyrene and phenothiazine and Cu(II), is presented. Although at different rates, all the sensitizers were shown to efficiently reduce Cu(II) to Cu(I) that catalyzes click reaction between model organic compounds. The applicability of the method for the construction of various macromolecular architectures including telechelic polymers and block copolymers was demonstrated. Spectroscopic and chromatographic investigations revealed that successful macromolecular syntheses were achieved.

Ali Görkem Yılmaz

İstanbul Technical University · Institute of Graduate Studies in Science

İstanbul Technical University · Institute of Graduate Studies in Science

ZnO yarı-iletken nanopartikülleri kullanılarak heterojen fotokataliz sistemi ile azid-alkin çıt-çıt reaksiyonu

In the past decade, selectivity, efficiency and diversity are the most important and required subjects for various reaction systems. "Click chemistry" can be given as an example for these systems offering remarkable advantages. Copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reactions between azides and terminal alkynes which developed by the groups of Sharpless and Meldal, have become the most popular click reactions to date. These reactions are versatile, regiospecific, and exhibit a high efficiency under mild reaction conditions with little or no by-products. Although there are a variety of metals that can be used as a catalyst for the azide-alkyne cycloaddition reactions, copper stands out as the only metal for the reliable, simple, fast and 1,4-regiospecific catalysis. With all these excellent features, CuAAC has found precious applications in different fields such as drug discovery, biochemistry, polymer chemistry and materials science. Recently, there is an explosive growth of research in the field of nanomaterials due to their operation for materials and devices using different techniques at nanometer scale. Nanoparticles are a part of nanomaterials that are defined as a single particles 1–100 nm in diameter and they have been a common material to develop new cutting-edge applications in communications, energy storage, optics, transmission, environmental protection, cosmetics, biology, and medicine due to their attractive optical, electrical, and magnetic properties. Moreover, nanoparticles can be combined with a wide range of metals and semiconductor core materials that bring in advantageous properties such as fluorescence and magnetic treatment. Amongs all the various types, zinc oxide - semiconductor metal oxide nanoparticles- are the most preferred type with their own importance due to their vast area of applications, such as, gas sensor, chemical sensor, bio-sensor, cosmetics, storage, optical and electrical devices, solar cells, and drug-delivery. In this thesis, a visible light-induced copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) strategy is carried out benefiting from the electron transfer reactions of zinc oxide nanoparticles (ZnO NPs) to achieve the required catalyst for the coupling process. Semiconductor ZnO NPs as a heterogeneous photocatalyst releases electrons on UV/VIS irradiation resuting in the photoreduction of air-stable copper(II) ions to copper(I) which is the catalyst of the CuAAC reaction A variety of azide and alkyne components has been examined and the system tolerates different substrates in the click reaction well. 1H-NMR and FTIR spectroscopy are used for the characterization of the reactions and it was determined that a triazole forms with the consumption of the starting azide and alkyne molecules.

Kadriye Özde Yetişkin

İstanbul Technical University · Fen Bilimleri Enstitüsü

Uç alkinler ile tiyollerin Cu(I) bağlanmış Schiff baz ağ polimeri katalizörü eşliğinde oksidatif çapraz dehidrojenatif birleştirme reaksiyonları

Alkynes are an important class of organic molecules because of their versatile applications in materials science and organic synthesis as building blocks. Sulfur-containing compounds have also a crucial role in synthetic organic chemistry since sulfur moiety acts as an important auxilary functional group. There has been an effort to combine these alkynes with sulfur-containing compounds by using metal-acetylides and sulfuryl halides or disulfides. However, these methods require a prefunctionalization progress of terminal alkyne or sulfur-containing coupling partners. This situation causes large number of side product formations which results in a dramatic decrease in the yields of reactions. Hence, the discovery of a new method to perform these reactions in high yields and better conditions gains a considerable attention. There are lots of studies on designing an useful catalyst to remove prefunctionalization processes and provide high yields and resusability. The term "catalysis" was first employed by Bezelius in 1836 tı ¸sdentify a new entity capable of promoting the occurrence of a chemical reaction by a "catalytic contact". In his view, the catalyst was seen as something that is added to the reaction to speed up the rate of the reactin (catalytic force) without being consumed or produced in the process. It is important to recognize that the catalysis can be traced back to the ancient terms. However, catalysis started to play a major impact on the chemical industry starting from the begining of twentieth century, nowadays more than 95 percent of chemicals being produced via a process that is at least includes at least one catalytic step. Traditionally, catalysts were distinguished into homogeneous and heterogeneous; subsequently, heterogenized catalysts were also introduced. This distinction is linked to the fact that the catalyst operates respectively in the same phase where the reaction occurs (homogenous catalysts) or in a different phase (heterogeneous or heterogenized catalysts). The main difference between a homogenous and heterogeneous catalyst is the fact that in case of homogeneous catalysts, every single catalytic entity can act as a single active site. This makes homogeneous catalysts more active and selective compared to traditional heterogeneous catalysts such as oxides or supported metal particles. A major drawback of the homogeneous catalysts is the difficulty of their recovery from the reaction medium. Precipitation with subsequent recovery or distillation of the reaction products, which is an energy intensie process, are typically needed in order to re-utilize homogeneous catalysts. Such operations may often deactivate the catalyst. Despite of these considerable advances, the problem with the homogeneous catalysis still remains to be unsolved. It is difficult to seperate catalyst from reaction mixture and reuse it. In contrast, design of an heteregenous catalysis should take increasingly more attention due to its possible advantages such as reusability, waste minimization derived from reaction workup and help to the development of green chemistry concept. xix Zhao et al. reported application of a hexagonally-ordered mesoporous material (MCM-41) supported bidentate nitrogen copper(I) complex [MCM-41-2N-CuCl] as a highly efficient and recyclable copper catalyst for the direct oxidative cross-dehydrogenative coupling of terminal alkynes with thiols using O2 as the sole oxidant under mild conditions to selectively afford a variety of alkynyl sulfides in good to excellent yields. According to their results, mesoporous material (MCM-41) has a extremely high surface area, large and uniform pore size, bidentate nitrogen copper complex can be easily formed and this complex can catalyze the coupling reaction between an alkyne and a thiol. In this thesis, the copper(I) incorporated microporous polymers' catalytic activity towards thiol-alkyne oxidative cross-dehydrogentavie coupling reactions without any prefunctionalization process was studied. In the first part of the thesis, the microporous network polymer was synthesized by melamine and terephtalaldehyde monomers through Schiff base chemistry. As known, the porous nature comes from the unique properities of monomers and frame of the polymer. In general, microporous organic polymers includes functional polar pendant groups such as amines, phenols or carboxylic acids since these groups can coordinate with metals. The rigid frame is also important for a ordered microporous structure. For that reason, aromatic conjugated structures or kinked aromatic high-performance polymers are used to have a rigid frame. Our choice of melamine and terephtalaldehyde as monomers is compatible with these criteria. Afterwards, the copper ions were incorporated into this microporous polymers and these materials were characterized. In the second part of the thesis, copper incorporated microporous Schiff base network polymer was used as a catalyst in the alkyne-thiol oxidative cross-dehydrogenative coupling reactions. The spectral and molecular weight analyses were applied to characterize the products.

Organic chemistry

Yonca Alkan