N-Karbazollerin yükseltgen polimerizasyon

Abstract

ÖZET Bu çalışmanın ilk bölümünde N-vinilkarbazol.karbazol ve N- etilkarbazolün seryum(IV) amonyum nitratın katalitik etkisiyle yükseltgen poiimerizasyonu elektrokimyasal polimerizasyonla karşılaştırmalı olarak incelenmiştir. Polimerizasyon reaksiyonuna monomer ve seryum(IV) derişiminin ve kullanılan çözücünün etkisi incelenmiştir. Susuz ortam olarak asetonitril (ACN) ve sulu ortam olarak toluen /su süspansiyon ortamı ya da polivinil alkol ve poliakrilik asit kullanarak oluşturulan dispersiyon ortamı seçilmiştir. Kullanılan seryum(IV) 'ün elektrokimyasal olarak geri kazanılacağı düşünülerek ACN ve ACN-H20 çözücü ortamlarında,anot ve katot bölmeleri ayrılmış elektrokimyasal hücrede polimerizasyonlar gerçekleştirilmiş, seryumun elektrokimyasal olarak geri kazanılması sonucu polimerizasyon veriminde artış sağlanmıştır. Elde edilen ürünler UV-Visible, FT-IR ve Floresans spektrofotometresi ölçümleri, elementel analiz v taramalı elektron mikroskobu (SEM), X-ray Floresans, pH, vizkozite, 4 nokta katı iletkenlik ölçümleri ve elektrokimyasal ölçümlerle karakterize edilmiştir. Monomer ve seryum(IV) konsantrasyonuna veya uygulanan potansiyele bağlı olarak polimerizasyon ortamında çözünebilen türde oligomerler ya da polimerler oluşabilmektedir. Seryum(IV) ile elde edilen polimerlerin ilk kez ölçülen iletkenlikleri kullanılan seryum(IV) miktarına ve ilave şekline bağlı olarak, literatürde diğer yöntemlerle elde edilen polimerlerin iletkenliklerinden daha iyi iletkenliğe sahip polimer elde edilmesinin mümkün olduğunu göstermektedir. İletkenliklerde daha fazla artış sağlamak üzere iletken özelliğe sahip olan pirol ile bu monomerlerin kopolimerleri sentezlenmiş iletkenliklerde artış elde edilmiştir. Çalışmanın ikinci bölümünde elde edilen polimerlerin bazı uygulamalardaki davranışları test edilmiştir. Polivinil karbazole suda çözünür özellikler kazandırarak değişik uygulamalarda kullanılabilirlik sağlamak amacıyla protein(BSA) ve poliakrilik asit matrisleriyle etkileşimleri incelenmiştir. Fotoiletken bir polimer olan beyaz PVCz ve fotokromik özeliklere sahip olan bazı spiro bileşiklerinden oluşan fotoduyarlı bir sistemde, PVCz'un spirobileşiklerin fotokromik aktivitesini azaltmadan tersinir olarak davranabileceği uygun bir polimer matrisi olduğu gözlenmiştir. NVCz'un CAN ile yükseltgen poiimerizasyonu sonucu elde edilen PVCz'den yüzeyde kimyasal olarak oluşturulan polimer filminin fotoaktif davranışları test edilmiştir. Yüzeyde oluşturulan polimer filmlerinin fotoaktif özellikler gösterdiği bulunmuştur. vııı

SUMMARY OXIDATIVE POLYMERIZATION OF N-CARBAZOLES The first paper on photoconductive polymers appeared in the early 1960s. The systematic research in this field came later. Poly(N-vinylcarbazole) (PVCz) has been extensively investigated one of the most promising thermal and photoconducting polymer. Although the conductivity of PVCz (1 0`5-1 0`7 S.cm`1) is lower by several orders of magnitude than that of polypyrrole or polythiophene (about 102 S.cm`1), PVCz still remains attractive owing to its properties e.g. electrochromism and photoconductivity. Several other possible applications such as image storage systems, photothermoplastic imaging, photovoltaic devices and non-conventional imaging systems have been reported in literature which have yet to be exploited commercially. A photoimaging system based on PVCz has been described by Smets. The component of the system are PVCz, CBr4 and a dye precursor, di- p- naphtospiropyran (DNSP). PVCz serves both a reactant in the image formation chemistry and as a binder. The mechanism involves photoproduction of acid (HBr) from the PVCz:CBr4 charge transfer complex. PVCz + CBr4 ^=± CTi hv CTi > HBr 405 nm Followed by reaction of the acid with the DNSP to produce a blue pyrylium dye latent image. Polycarbazole is a conductive polymer whose conductivity is comparable to that of polypyrrole. During the investigation on the electrochemistry of carbazole in different non-aqueous solvents such as acetonitrile, methylene chloride, a green film on the electrode surface which also exhibit specific catalysis in electrooxidation of organic molecules has been generated. IXThe industrial and academic studies have played a significant role in advancing the understanding of photoelectronic phenomena in organic and polymeric solids. The polymerization of carbazole derivatives especially NVCz has lately attracted the attention of many researchers. Although there is some reports on polymerization of NVCz by using oxidizing metal salts, mechanism of polymerization has not been clarified completely. The monomer N-vinylcarbazole is readily polymerized by free-radical and cationic methods. This results from its ability to stabilize electron-deficient centres by resonance involving the nonbonding electron pair on the N atom of carbazole ring. Attempts to polymerize to monomer anionically were unsuccessful. Polymerization by Ziegler-Natta type catalysts has been questioned. The related N-alkyl-2-3-, and -4-vinylcarbazole monomers can be polymerized by radical, cationic and anionic methods. In the first part of this thesis, oxidative polymerization of N-vinylcarbazole (NVCz) N-carbazole (Cz), N-ethylcarbazole (ECz) by using eerie ammonium nitrate (CAN) as catalyst in acetonitrile were studied comparatively with electrochemical polymerization. Depending upon the relative concentration, the precipitation of brownish and dark green powder were obtained for NVCz, Cz and ECz respectively. For NVCz at high nmon/nCAN ratios precipitate of PVCz in white colour also formed. Polymerization products analyzed by elemental analysis, FT-IR, X-Ray Fluorescence (XRF), Scanning Electron Microscope (SEM), viscometry, pH, electrochemical and four probe conductivity measurements suggest that initiation process was most likely to be of the electron transfer type. Polycarbazoles obtained with oxidative polymerization by using CAN have higher conductivities than obtained by electrochemically If the monomer and CAN concentration are lower than a critical concentration soluble intermediates formed in acetonitrile. The solutions were analyzed by UV-visible spectrophotometer. The appearance of new absorption bands in visible range suggest the formation of oligomers. At the end of oxidative polymerization Ce(IV) is reduced to Ce(lll), which can be electrochemically regenerated and can be reused to initiate the polymerization. On the other hand, studies on the electropolymerization of acrylamide with carboxylic acid-Ce(IV) show that the electrolysis method comparing with nonelectrolytic or conventional method at a very low concentration have many advantages. This process is especially suitable for commercial polymerization of vinyl monomer because the initiator can be continuously in-situ generated and, lower Ce(IV) concentration is required by comparing with conventional method.So in this study, effect of electrogeneration of Ce(lll) on the polymerizaiton yield firstly applied to N-vinyl carbazole in a divided electrochemical cell. According to all results obtained, a suitable mechanism for chemical and electrochemical method was proposed. ®CH2- CH I nNVCz >. -<CH2`fH^ N 55 White PVCz For the electroregenerated conditions Ce (III) can be electrochemically oxidized to Ce(IV) and reused for initiating the polymerization: NVCz +Ce(IV) = NVCz+- + Ce (111) Electroregeneration XIOxidation -e` I) CAN 'OApplied Potential R-Cz at low CAN concentrations Polymerization Dark green polymers R= - CH = CH2 ( N-vinylcarbazole, NVCz) - H ( Carbazole, Cz) - C2H5 (N-ethylcarbazole, ECz) XllWhile there is some literature on the role of water in the preparation of conductive polypyrrole, polymerization of carbazole derivatives in water has not been attracted the attention because of their insolubility in water. In the second part of this study, oxidative polymerization of NVCz, Cz and ECz in water in the presence of water soluble polymers such as poly(vinylalcohol) and polyacrylic acid as dispersion agent firstly applied with the aim of enhancement in the conductivity. It is known that suspension polymerization of N-vinylcarbazole in toluene/water-solvent induced by FeCI3 yields a polymer with appreciably higher conductivity than that of a conventionally prepared PVCz. These biphasic system firstly applied to carbazole and ethylcarbazole by using CAN as catalyst instead of iron (III) chloride. It is found that presence of PAA and PVA leds better dispersion of monomer and resulting polymers has the conductivities lower tan 1 0`6 S/cm. On the other hand, since the monomers are soluble in toluene, both the polymerization yield and conductivities are higher than in the case of dispersion polymerization. Attempt have been made to copolymerize different kinds of heterocyclic compound with the aim of improving the properties of the resulting copolymers. For this purpose, N-vinylcarbazole, carbazole and N-ethylcarbazole was copolymerized with pyrrole since the oxidation potentials of the monomers are comparable and the conductivity of polymer of the latest monomer is better than the others. Although the electrochemical copolymers of pyrrole and N- vinylcarbazole have been studied, copolymerization of pyrrole with carbazole and N-ethylcarbazole by using CAN is out of our knowledge. The copolymers characterized by FT-IR spectroscopy, exhibits improved conductivities and decreases the brittelness relative to homopolymers of carbazoles. In the last part of thesis some applications of polymer were tested. Some interaction between protein (Bovine Serum Albumin, BSA) or anionic polyelectrolyte (Polyacrylicacid.PAA ) and PVCz was investigated with the aim of testing possible applications of PVCz as a biopolymer. The other possible application of photoconductive PVCz is to use of it a photosensitive system containing carbontetra chloride as activator and some spirocompounds as dye-precursor which can be used as latent image formation. It this system effect of white PVCz obtained by oxidative polymerization with CAN, on the decolorization reaction of spirocompounds has been investigated by UV-visible spectrophotometric measurements. It is found that PVCz binder is not only a matrix in which the photochemical free-radical mechanism proceeds, but it plays active role in the latent-image formation as well as in its optical development through complex formation with carbon tetrachloride. On the other hand, white PVCz which polymerize only through vinyl groups is a water-insoluble photoconductive polymer having a high optical transparency. This property makes it resistant to humidity and environmental xiiiperturbation and gives some advantages for using as a photoconductive polymers. Transparent poly(N-vinylcarbazole) film was prepared by casting from toluene+cyclohexanone solutions on the Pt and pyrite electrodes. To remove the rest of the solvent samples were dried in vacuum. Then photoactivity of PVCz coated electrodes were investigated. It was found that chemically prepared transparent PVCz film on pyrite surface exhibit better photoactivity than that of on Pt surface due to some interaction between pyrite and polymer. XIV