Akrilonitrilin Poliakrilik Asit Varlığında Kimyasal Ve Elektrokimyasal Yöntemlerle Yükseltgen Graft Kopolimerizasyonu

Abstract

Bu çalışmada, boya ve ilaç sanayinde çokça kullanılan dispersiyon polimerleri elde edilmeye çalışıldı. Bu amaçla, monomeri suda az miktarda çözünen, polimeri ise çözünmeyen Akrilonitrilin (AN), çalışmanın ilk kısmında Ce(IV) varlığında kimyasal ve elektrokimyasal yöntemlerle polimerizasyonu gerçekleştirilerek. Bu yöntemler üzerine polimerizasyonda kullanılan değişkenlerin etkisi incelendi (monomer, başlatıcı, asit, konsantrasyonları ve zamanın etkisi). Çalışmanın ikinci kısmında dispersiyon polimerizasyonu gerçekleştirmek üzere, akrilonitrilin polimerizasyonu sırasında yapılan denemeler, dispersant olarak poliakıillk asit kullanılarak ile tekrar edildi ve değişik koşullar ve parametreler kullanılarak optimum dispersiyon koşullan elde edilmeye çalışıldı. Bu yöntemle çökme polimerizasyonu ile polimerteşen akrilonitril poliakirllik asit varlığında İnce tanecik boyutunda ve dispers halde elde edilmiş oldu. Elde edilen numunelerin tanecik büyüklüğü tane boyut ölçüm cihazında (Multî Sizer) alınan değerlerin, diğer deney koşulları ile olan ilişkisi incelendi. Polarize mikroskop kullanılarak gerçekleştirilen ölçümlerle tane boyut değerleri karşılaştırıldı. UV-visible Spektrofotometre ile yapılan ölçümler sonucu elde edilen absorbans değerlerinden, reaksiyon kinetiği ile ilgili bilgiler elde edilere, bu sistemin Rayleigh eşitliğine uyup uymadığı kontrol edildi. Ayrıca bu çalışmada elde edilen tanecik boyuttan denel koşullara bağlı olarak dar tanecik boyut dağılımı göstermektedir ve bunların denel koşullara bağlı olmak üzere 1-5 um arasında olduktan gözlenmiştir

Electroinduced Graft Copolymerization of Acrylonitrile with Polyacrylic Acid, Resulting Monodispers PAA-g-PAN Particles. Micron size monodisperse polymer particles are used in a wide variety of applications such as tuners, instrument calibration standarts, cloumn packing materials for chromatography, model systems, and biomedical and biochemical analysis. Because of the commercial and scientific interest in these particles, preparation of these microspheres has been an active research field in recent years. Monodispers particles in the micron-size range are diffucuit to obtain because this size is just between the diameter range of particles produced by conventional emulsion polymerization (0.1-0.7 um) and suspension polymerization (50-100 um). Dispersion polymerizations have received much attention as a simple and convenient method to prepare monodispers polymer particles in the micron size range. Dispersion polymerization is commonly used as a unique method forming particles in a single step with sizes ranging from ca. 0. lum up to ca. 15um. Under appropriate conditions these particles may be formed with a very narrow size distribution. Such particles, prepared from a variety of monomers ie.. styrene, chloromethylestyrene,... The mechanism of dispersion polymerizatiom is complex and poorly understood. Dispersion polymerization processes are composed of two major stages: (a) nuclei formation and then (b) nuclei growth. At the start of the process, the monomer, stabilizer (surfactant), and initiator are dissolved and form a homogeneous solution in the continuous phase. Upon polymerization, the initatior radicals react with solute monomer molecules to form oligomeric radicals which at a critical chain length precipitate as small nuclei. These nuclei may then grow to the final size by a variety of mechanisms, ie.. agglomeration of small nuclei, polymerization of the monomer in the swelled nuclei, and seeded polymerization of the monomer on the nuclei surfaces. The stabilizer in the dispersion polymerization is adsorbed on the particle surfaces and thereby stabilizes the particles by a process which is only qualitatively understood. The particles stop growing when all of the monomer consumed and/or when the stabilizer is adsorbed and forms a retatievly packed coating on the particle surfaces. The stabilizer adsorption on the particles surfaces depending on its packing, may prevent, or significantly decrease, some or all, of the processes previously described through which the nuclei grow to their final size. Dispersion polymerization processes were previously investigated in two main continuous phase classes: hydrocarbons and polar solvents, such as alcohols. It was clearly demonsrated that various conditions, such as the nature of the stabilizer, stabilizer concentration, initiator concentration, etc. play may important role in determining size, size distribution, and moleculer weight of the formed particles. However, there is still a lack of basic understanding of the reason for these changes and also inconsistency in the reports on yhe effect of a few of these changesj.e., a few reports claim that increasing the stabilizer or initatior concentration causes a decreases in the particles size while other claim no significant change. Barett has prepared poiymethyl methacrylate monosize microbeads in hydrocarbon media. Almong et al. have reported the preparation of monosize polystyrene and poiymethyl methactylate microbeads up to 5 um. Corner has described polystyrene microbeads produced in aqueous ethanol media using poliacrylic acid as the steric stabizer. Ober and his coworkers have produced monosize polystyrene microbeads up to 9 um by polymerization of styrene in a variety of solvent systems (e.g., 2- methoxyethanol/ ethanol ) by using different nonionic cellulosic polymers as steric stabilizers (e.g., hydroxypropylcelluiose) with no charged cosurfactants. They were also successful in forming large monosize copolymer microbeads by dispersion polymerization in the presence of poryacrylic acidas asteric stabilizer. Paine et al.studied dispersion polymerization of styrene in alcoholic media in the presence of poly(N-vinyl pyrrolidone) as a steric stabilizer. They have reported the production of monosize polymer microbeads up to 18 um in size. Paine has also proposed a simple mathematical model to predict the particle size in dispersion polymerization of styrene in polar solvents. Okubo et al. Have reported preparation of monosize polymer microbeads having chloromethyl groups by following two-step polymerization in a dispersion medium consisting of water/ethanol mixtures. In this study chemical and electrochemical dispersion polymerization of acrylonitrile was carried out in the presence of polyacrylic acid, cerium(IV), sulfuric acid, under various experimental conditions. By the electrochemical method anode and cathode seperated from each other by a frit. The effects of poliacrylic acid, acrylonitrile, cerium(IV), and sulfuric acid concentration on the polymerization and size of the dispersant was studied in detail. For comparison purposes electrochemical and chemical polymerization of acrylonitrile was carried out under different experimental conditions. The results were given in Table (1 ). From the Table (1), can be seen that increase in the monomer concentration and than it reaches a constant value. XI Table 1 Effect of monomer concentration on the chemical and electrochemical polymerization of acrylonitrile on the reaction yield. >(Ce(IV))=3.3. lfJ3M, (H^O^O- 1 3 M, T=50°C/ 1 =90 minute" Chemical and electrochemical polymerization of acrylonitrile in the presence of polyacrylic acid as a dispersant was also studied under different experimental conditions. Chances in the monomer concentrations does not effect the size of the particles which is between 1.18-1.20 um (Table2). Solids content of the solution of the polymer does not also show increase due to precence of poliacrylic acid both in the beginning and end of the reaction (Table2). Table 2 Effect of the monomer concentration on the chemical and electrochemical solution polymerization of acrylonitrile in the presence of polyacrylic acid on particle mean diameter and solid content. "(Ce(PV))=3.3.10"3 M, (HsSO^O.lS M, (PAA)= 0.12M, T=50°C, t =180 minute *MD=Mean Diameter, SC=Solid Content Effect of the initiator on the chemical and electrochemical dispersion polymerization of acrylonitrile by cerium (IV) shows an increase in the solids content of polymerization reaction by increasing cerium(IV) concentration up to about l.öö.lO^M for chemical polymerization (Table 3 ). But on the other hand elctrochemical polymerization of acrylonitrile in the presence of poliacrylonitrile exhibits an increase in the mean particle diameter from about 1.0-2.0 um to 8.0-9.0 um by increase in cerium(rV) concentration. This might be due to the presence of more micelles which is formed by coagulation of acrylonitrile particles with poliacrylic acid, the production of more micelles of high concentration of cerium (IV) is due to regeneration of cerium (III), on the cerium (IV) elctrode surface which causes more electron transfer from cathode results radical anions. XU Table 3 Effect of the initatior concentration on the chemical and electrochemical solution polymerization of acrylonitrile in the presence of polyacrylic acid on particle mean diameter and solid content. "(AN}=0.40 M, (H2SO4)=0.13 M, (PAA)= 0.12M, T=50°C, t =180 minute"MD=mean Diameter, SC=Solid Content The efffect of surfactant (polyacrylic acid) and acid concentration on the chemical and electrochemical dispersion polymerization of acrylonitrile also causes a slight increase in the solid content of reaction solution (Table 4.5). Table 4 Effect of the surfactant concentration on the chemical and electrochemical solution polymerization of acrylonitrile in the presence of polyacrylic acid on particle mean diameter and solid content. "(AN)=0.40 M, (H2SO4)=0.13 M, (Ce(IV))= 3.3. 10"3 M, T=50°C, t =180 minute"MD=Mean Diameter, SC=Solid Content Table 5 Effect of the acid concentration on the chemical and electrochemical solution polymerization of acrylonitrile in the presence of polyacrylic acid on particle mean diameter and solid content. "(AN)=0.40 M, (CeOV)=3.3.10"3M, (PAA)= 0.12M, T=50°C, t =180 minute"MD=Mean Diameter, SC=Solid Content XUl For the effect of the temparature on the chemical and electrochemical dispersion polymerization of AN, temparature was increased it was found the temparature causes a slightly decrease in the solid content of the reaction solution. For chemical dispersion polymerization causes a gradual decrease in the particle size diameter (Table, 6). by decrease in temparature, this might be due to the homopolymer of AN. Tablo 6 Effect of the temparature on the chemical and electrochemical solution polymerization of acrylonitrile in the presence of polyacrylic acid on particle mean diameter and solid content. "(AN)=0.40 M, (Ce(IV)=3.3.10"3M, (PAA)= 0.12M, T=50°C, t =180 minute"MD=Mean Diameter, SC=Solid Content Reaction mechanism which was proposed for the AN polymerization in PAA dispersion medium is following: /; Initiation Ce(IV) M R« Ce(lll) (1) and/or X(H2Q) 2) Propagation R« RM- M RM« RMn* (2) 3) Termination RMn- + RMn- Rmn» + Ce(IV) " or anodic RMn-nMR (Polymer) (3) RMn (Polymer) For this study following conclusions can be drawn: Yield of homopolymerizatlon of acrylonitrile in electrochemically induced polymerization about 3 times higher than chemical polymerization. By chemical and electrochemically in polyacrylic acid stabilizer, acrylonitrlle polymerization (using ceriun(IV)) give homogenous dispersion polymerization In electrochemically induced polymerization of acrylonitrile in polyacrylic acid stabilizer in the presence of cerium(rV) gives micron size particul containing dispersions, with a narrow size distribution. XIV BOLUM 1 GİRİŞ ve AMAÇ Dispersiyon polimerizosyonu, mikron büyüklükteki monodispers polimer taneciklerinin hazırlanmasında kullanılabilecek en kolay ve en pratik yöntemdir [I]. Dispersiyon polimerizasyonunun mekanizması çok kompleks ve anlaşılmazdır. Çekirdeğin oluşumu ve büyümesi olmak üzere iki aşamadan oluşur [2]. Dispersiyon polimerizosyonu ile tek basamakta 0.10 um'den 15 um'ye kadar çeşitli büyüklükte tanecikler elde edilebilir [3]. Mikron büyüklükteki mono dispers polimer taneciklerinin; kalibrasyon aletlerinin standardizasyonu, kromatografik kolonların kaplanması, biyomedikal ve biyokimyasal analizler... gibi birçok kullanım alanı vardır [4]. Ticari ve bilimsel açıdan, bu tür taneciklere duyulan ihtiyaçtan dolayı son yıllarda bu alandaki çalışmaların sayılan çok artmıştır. Ce(IV) tuzlarının sulu asidik çözeltilerinin vinil monomerlerini polimerleştirebildikleri bilinmektedir [6]. Ce(IV) ve indirgeyici bir madde örneğin alkol [7.8], keton [9], glikol, aldehit, karboksilli asit [10] arasındaki redoks reaksiyonlarıdır. Bu reaksiyonlar sonucu Ce(IV) vinil monomerlerini polimerleştirebilecek şekilde radikaller oluşturur. Bu çalışmanın ilk kısmında da, grubumuzda daha önce yapılmış çalışmalar gözönüne alınarak [5]. Akrilonitrilln (AN), seryum (IV) sülfat (Ce(IV)) tuzuyla kimyasal ve elektrokimyasal yöntemlerle polimerize edilmesi amaçlanmıştır. Polimerizasyon yöntemleri üzerine, polimerizasyondaki değişkenlerin ( monomer, asit, başlahcı konsatrasyonlan ile zamanın) etkilerinin incelenmesi amaçlanmıştır. Çalışmanın ikinci kısmında ise, birinci kısımdan elde edilecek sonuçların ışığında, akrilonitril monomerinin poliakrilik asit varlığında kimyasal ve elektrokimyasal yöntemlerle dispers edilmesi, ilk kısımda olduğu gibi bu yöntemlere reaksiyon ortamındaki değişkenlerin etkisinin incelenmesi ile optimum dispersiyon polimerizayonu koşullarının elde edilmesi amaçlanmıştır.