Polimer mikro küreleri üzerinde polianilin sentezi ve amin, amino asit immobilizasyonunda kullanımı
Preparation of pani coated polymer microspheres and their use as michael acceptor for direct immobilization of amines and amino acids
Yazar: HASAN ONUR ERDEM
Danışman: PROF. DR. NİYAZİ BIÇAK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Ana Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: Kimya = Chemistry
Dizin: Blok polimerler = Block polymers ; Radikal polimerleşme = Radical polymerization ; Stiren polimerleşmesi = Styrene polymerization

Özet:
Poli anilinin (PANI) ucuz maliyetinin yanında iletken bir polimer özelliği göstermesi, hava oksidasyonuna karşı dayanıklı olması, basit hazırlanabilme özellikleri sebebiyle üzerinde uzun yıllardır çalışılmıştır. Günümüzde de bu özelliklerinin yanında diğer kullanım alanları ortaya çıkmış ve üzerinde hala yoğun olarak çalışılmaktadır. 
Bu çalışmada PANI tabakası, poli (stiren-divinil benzen) (PS-DVB) küreleri üzerinde oluşturuldu. Bu amaçla öncelikle süspansiyon polimerizasyonu ile PS-DVB küreleri sentezlendi ve küreler atom transfer radikal polimerizasyonu (ATRP) için bromlandı. Daha sonrasında bromlanan uçlardan ATRP ile poli stiren saçaklar oluşturuldu. Bu saçaklardaki stiren grupları sülfirik asit ile fosfor pentaoksit varlığında sülfolandı. Sülfolanmış mikro küreler anilin ile nötralize edildi. Nötralize edilen anilin potasyum persülfat ile polimerleştirildi ve 'Emeraldine green' yapısı elde edildi. Sonrasında oksidasyona devam edilerek 'Pernigraline' yapısı oluşturuldu. Küre yüzeyinde oluşturulan 'Emeraldine green' ve 'Pernigraline' tabakaları SEM-EDX, FT-IR, TGA ve kalitatif ölçümler ile kanıtlandı. Ayrıca beyaz olan kürelerde 'Emeraldine green' tabakası oluşturulduğunda renk yeşile, 'Pernigraline' tabakası oluşturulduğunda ise renk kırmızıya döndü. Bu renkler de polimerlerin kendi özgül renkleridir. Reaksiyon akışının kalitatif gözlemle takibi bu yolla sağlandı.
Mikro kürelerin SEM fotoğrafları incelendiğinde sülfonlanmış kürelerin, düzgün yüzeyli küresel yapıda olduğu görülmüştür. Sülfolama ve nötralleştirme reaksiyonlarında, reaksiyon buz banyosunda gerçekleştirildi. Bu sayede kürelerin ortaya çıkan ısıdan zarar görmesi engellendi. Oksidasyon sonunda ise kürelerin küresel yapısı bozulmadığı SEM analizi ile belirlendi. Fakat oksidasyonun oda sıcaklığında gerçekleştirilmesinden dolayı, küre yüzeylerinde kısmi olarak hasarların oluştuğu görüldü. 
Dört uç metodu ile yapılan iletkenlik ölçümlerinde, sentezlenen sülfolanmış ve Pernigraline kaplı mikro küreler yalıtkan özellik gösterdi. Emeraldine formu ise beklenildiği üzere iletken özellik gösterdi.
Pernigraline yapısı etkin bir 'Michael Akseptör' özelliği göstermektedir. Bu özelliğinden faydalanarak amin, amino asit ve poli amin gruplarının küre yüzeyinde immobilizasyonu araştırıldı. Katılma reaksiyonun gerçekleştiği; kütle artışından ve FT-IR ölçümlerinde katılma veren bileşiklerin içerdiği spesifik pikler ile ispatlandı. 
Çalışma sonucunda Pernigraline kaplanmış küreler amin gruplarının immobilizasyonunda kullanılabilirliği ortaya konmuştur. Bu sonuçlardan yola çıkılarak, gelecek çalışmalarda bu yapının amino asit kiral ayrımında kullanılması planlanmıştır.

Abstract:
Polyaniline (PANI) is one of the most important and oldest members of inherently conducting polymers. Its tunable electrical conductivity, excellent stability to air oxidation and simplicity of its preparation from cheap materials makes it promising candidate for preparing light-weight batteries, electrochromic devices, sensors and electro-luminescent devices.
Traditional method of aniline polymerization involves oxidation of anilinium salts with the oxidants such as, potassium or ammonium persulfates, FeCl3 and MnO2 in aqueous solutions. This method yields insoluble PANI, so called "Emeraldine Green". A great deal of work has been devoted to enhance solubility and conductivity of PANI. Interestingly, polymerization of aniline in the presence of polyacids such as, poly (4-styrene sulfonic acid) and polyacrylic acid has been reported to give doped and soluble PANIs. This can be ascribed to template effect of the polyacids.
Catalytic air oxidation of aniline without acid has been demonstrated to give high molecular weight and soluble PANI in Emeraldine base form. Recently Kitani group developed electro-polymerization process yielding microspherical PANI in the presence of DNA as template. Zhang et al described preparation of urchin-like PANI microspheres without using template. Microspherical PANI has been considered as potential candidate as sensor materials due to its relatively easy modification especially by Michael addition via quinonimine moieties of its Pernigraline form. Having considerable reactivity for Michael addition, fully oxidized form of PANI, pernigraline was considered as good candidate for immobilizing appropriate reagents and catalyst carriers.
Taking these into consideration, in the present work we have studied polymerization of anilinium salt formed on sulfonic acid functional linear poly (styrene) brushes tethered to the cross-linked poly (styrene-divinyl benzene) (PS-DVB) micro spheres. The base material was prepared starting from (PS-DVB) micro beads (210-420 μm) in three steps:
 i) Immobilization of bromoacetyl groups,
 ii) Surface initiated ATRP of styrene,
 iii) Sulfonation by sulfuric acid-phosphorous pentoxide mixture.
Two resin materials with 176.7% and 550.4% PS graft yields were prepared by copper mediated ATRP of styrene starting from bromoacetyl surface groups (0.81 mmolg−1 ) by assuming 0.7 as average initiation efficiency of the surface-bound initiator groups, such graft densities account for about 30 and 93.2 average repeating units in the graft chains. Sulfuric acid–phosphorous pentoxide mixture (or so called Eaton reagent) was employed for sulfonation of PS grafted beads after swelling in CH2Cl2. Titration of the sulfonated resins indicated 4.2 and 4.8 mmolg−1 of the sulfonic acid groups. For preparing PANI coated micro beads, the sulfonated samples were soaked into an aniline–water mixture (1/10) in an ice-bath, to avoid mechanical disintegration of the particles due to the heat of the neutralization.
After that, aniline is first fixed on sulfonic acid groups forming anilinium sulfonate salt. In the second stage, the surface bound aniline polymerizes by persulfate addition alongside the graft chains. Initiation of the aniline polymerization can be followed visually by immediate darkening of the microspheres upon addition of persulfate. The spaces between the graft chains must be filled up with PANI. PS–DVB microbeads represent perfect spherical shapes after four step modifications yielding sulfonated polymer brushes, as shown in the SEM picture. A significant mass increases occurred in polymerization of aniline, while retaining the spherical shapes. However, surfaces of the deep black particles gain somewhat roughness, probably due to local effect of the heats of neutralization. Although the salt formation of the sulfonic acid groups is performed in an ice bath, the neutralization causes to local heating and some mechanical disintegration. Indeed when the neutralization is carried out at room temperature, the spherical shape of the particles disappeared almost completely as visually observed through an optical microscopy.
The anilinium sulfonate moieties generated on the surface brushes were first oxidized to Emeraldine Green and then to Pernigraline. The quinoneimine moieties of the Pernigraline layer are expected to show high reactivity for the nucleophylic additions (Michael addition) as in the case of quinones. There appears to be few reports on chemical modification of PANI in various oxidation states, such as sulfonation, chlorination and diazo-coupling reactions. Han and Jeng reported nucleophilic addition of amines and thiols to quinonimine rings of pernigraline as a powerful method for the post-modification of PANI. The addition of sulfite ions has been demonstrated to give ring sulfonation in high yields. It is important to note that, these reactions occur in reasonable yields, although PANI has very limited solubility in most cases and the quinoneimine rings of pernigraline form turn to benzenoid rings by nucleophilic addition. In the current study, Michael addition capability of fully oxidized PANI was studied for addition of amino acids (glycine and l-alanine) and some polyamines (polyethylene imine) and triethylene tetramine in addition to benzyl mercaptane. 1 M aqueous amino acid solutions were used in the experiments and extents of the Michael additions were assigned by analysis of residual amino acids using the ninhydrine method.
The addition reactions were carried out by contacting alcohol solutions of amines and thiols. Acid and base titration methods were employed for the estimation of the amine and thiol additions respectively. The addition yields of the selected nucleophyles are listed. All the addition experiments showed detectable mass increases. For instance, addition of benzyl mercaptane and poly (ethylene imine) showed significant mass increases (19% and 14% respectively). To prove the Michael addition of TETA, a qualitative test was carried out in which 0.5 g TETA adduct was treated with 20 mL of 0.1 M CuSO4 solution. An immediate characteristic deep violet color developed on the microspheres, but no color was observed in the aqueous phase. This indicates chelating of TETA with copper; hence it's bonding to the solid surface via Michael addition. FT-IR spectra of the Michael adducts, however did not show characteristic peaks different from those of the pernigraline. For instance, FT-IR spectrum of the glycine treated sample shows only intensifying peak at 1640 cm−1. This band appears also in the spectrum of the oxidized PANI. Additional broad band in 3300–3600 cm−1 range that can be ascribed O–H stretching vibration of the carboxyl group. Moreover, the N–H plane bending vibration bands of the added amines and amino acids are not discernible due to presence of the peak of the base material in the same region. To attain clear cut evidence, the PANI sample was treated with 2- cyanoethylamine in situ generated by reaction of ammonia solution with acrylonitrile. The FT-IR spectrum of the resulting product shows a characteristic nitrile group stretching band at 2249 cm−1 indicating addition of the amino group to the quinonimine.
As a conclusion anilinium salts of sulfonated polystyrene brushes on PS–DVB microspheres can be oxidized to give dark microspheres possessing nearly 23–26% PANI. The reaction takes place selectively on the particle surfaces and gives a conducting PANI layer as evidenced by four-pointprobe technique. In TGA measurements the PANI or Pernigraline coated microspheres do not show any mass loss up to 700 °C under nitrogen flow. In air atmosphere however decomposition of PANI or pernigraline layer simultaneously with sulfonic acid groups in 306–512 °C range. Further oxidation of the PANI layer turn into a non-conducting Pernigraline which is a high capacity. The Michael acceptor solid matrix is capable of adding various nucleophyles including amino acids. Such an amino acid binding of surface bound Pernigraline via Michael addition has not been reported so far. Amino acid immobilizing capability of the pernigraline might be useful for preparing chiral stationary phases for chiral separation of amino acids etc.