Seryum(IV)-poliaminokarboksilli asit redoks başlatıcılı akrilamid polimerizasyonu

Abstract

Seryum (IV) sülfat çok hizlı elektron transferi yapabilen oldukça kuvvetli yükseltgen maddedir ve bu özelliklerinden yararlanılarak serbest radikal polimerizasyonunda bir organik asit beraberliğinde başlatıcı olarak kullanılabilmektedir. Bu çalışmada, akrilamidin poliaminokarboksilli asitler ile yapılan serbest radikal polimerizasyonunda organik bir asidin yardımıyla baş latıcı olarak Seryum(IV) kullanılmıştır. Titriplex I, Titriplex III, Titriplex V, Titriplex VI kullanılan poliaminokarboksilli asitlerdir. Çalışmada yapılan deneylerde sıcaklık, reaksiyon süresi, Sülfürik asit, Seryum(IV), Titriplex I, Titriplex III, Titriplex V, Titriplex VI konsantrasyonları değiştirilmiş ve bunların polimer verimi ile polimerlerin molekül ağırlığına etkisi incelenmiştir. Sonuçta düşük Seryum (IV) konsantrasyonlarında verimin düştüğü ve Seryum(IV) konsantrasyonunun artmasıyla verimin arttığı gözlenmiştir. Reaksiyon süresinin artmasıyla da polimer veriminde artış görülmüştür.

Free radical chain polymerizations have become most important polymerization method as far as their industrial utilization is concerned. "The propagating side is a free radical, an unpaired electron at the last carbon atom of the growing chain. A free radical polymerization thus involves many successive steps of growth. A monomer molecule is added to the chain, where by the radical side is reformed on the newly fixed last unit of the chain. Initiators : The free radical initiators can be classified in several groups, of which the most important are : a) Peroxides, organic or inorganic, like dibenzoyl peroxide or potassium peroxodisulfate b ) Hydroperoxides c ) Peresters d) Aliphatic azocompounds UV irradiation is used sometimes to help cleave the initiator molecule. Radical sides can also be created by a large variety of oxidation reduction processes, as in the examples quoted below : 3+ 2+ - Fe + H 0 ^ Fe + OH + OH 2 2 4+. 3+ + R-CH -OH+Ce > R-CH-OH+Ce +H 2 Mechanism of Radical Chain Polymerization Initiation Initiation : The initiation reaction is the attack of a monomer molecule by a primary radical originating from the initiator. This process involves two reactions. 1. Decomposition of the initiator to form primary radicals 2R 2. The actual initiation reaction R + M -> RM* Propagation : It can be written as RM' + M > RM* n n+1 Termination : By recombination R - M + R - M n p -> R - M - R n+p Acrylamide Polymer : This study deals primarly with acrylamide itself because it is the most important industrially and because its properties are the best known in the presence of free radicals acrylamide polymerizes rapidly to high moleculer-weight polymers. Common initiators are peroxides, azo compounds, redox pairs, photo- cnemical systems and x rays. Polymerization in aqueous solution is generally the preferred method. Organic liquids that are solvents for the monomer may be used as reaction media. In this event the polymer is newly always insoluble and precipitates as it forms. Drying problems are reduced, but the moleculer weight of polymer made in this way may be too low. Redox catalysts are used for aqueous polymerization. Common examples are the peroxydisulfate-bisulfite couple, and peroxide with ferrous ammonium sulfate, ionizing radiation has been studied extensively as an initiator for aqueous systems as well as for the crystalline monomer. Acrylamide solutions containing certain dyes polymerize rapidly when exposed to ultraviolet light. VI The mechanism of free radical polymerization of acrylamide has o been studied extensively. At 25 C the rate constant is reported as, 4 -1 -1 k = 1.8x10 1-mole -sec P 7-1-1 k = 1.45x10 1-mole -sec * -1 -1 -1 k = 2.2x10 1-mole -sec tm for propagation for termination for transfer The ratio k /k exceeds that reported for any other monomer, k St p y high and k rather low. Moleculer weight may be requlated by alcohols, as mentioned earlier, by mercaptans, and by other transfer agents. Some inorganic salts are highly effective. The bisulfite ion, present in many redox systems, has a chain transfer constant of about 0.17. Ferric and vanadyl ions are among the cations that terminate chains effectively and are themselves reduced by a one electron transfer. A useful property of acrylamide is its ability to form soluble polymers of extraordinarily high moleculer weight. Moleculer weights are difficult to measure accurately but may reach at least 10 million. The product may be water-soluble, but concentrated solutions and high temperature or very long reaction times tend to produce water-insoluble polymers. CH -CH 2 i CÜNH CONH CH -CH 2 CH -CH - 2 « C=0 NH + NH 4 C=0.CH -CH - 2 Substituted acrylamides and methacrylamides having the general formula. Vil Substituted acrylamides and methacrylamides having the general formula. R1" CH - C - 2 I CONR. R" yield polymers ranging from hard and brittle to soft and tacky. Polyacrylamide itself is substantially insoluble in nearly all organic liquids. Exceptions are some acids (acetic, acrylic, lactic and chlorinated acetic acids), some hydroxy compounds (ethylene glycol glycerol), and some nitrogen compounds (form-amide, molten urea). In the course of an investigation of the graft copolimerization. of acrylamide onto cellulosic fibers, it became desirable to study homopolymerization of acrylamide initiated by eerie ion, which had been found to be a side reaction of graft copolymerization initiation of radical polymerization by eerie ion is also known in the case of methyl acrylate. Mino proposed the following termination reaction : R* + Ce(lV) 5» Polymer + Ce(IIl) + H+ (R* = polyacrylamide radical) But the end group of the polymer thus obtained has not yet been determined CAVELL has studied the kinetics of radical polymerization of acrylamide in the presence of ferric or vanadium perchlorate and discussed the termination mechanism with those salts. Ce( IV) salts-reducing agent systems are well known initiators for vinyl polymerization, especially for graft copolymerization of vinyl monomer such as acrylonitrile and acrylamide. Block copolymers were also prepared with this system. The polymerization mechanism involves the generation of free radicals from the complex formed between Ce(IV) salt and reducing agent following the formation of free radical which initiates the polymerization of vinyl monomer. In this work, the Ce(IV) polyaminocarboxylic acids redoxs systems were used to initiate polymerization of acrylamide. vm Polymerization was carried out in a three necked flask. Aqueous solution of acrylamide and polyaminocarboxylic acid were added into the flask and the stirrer started. Ce(IV) salt solution was added dropwise in 3 minutes. After certain period of polymerization time, the content of the flask was poured into the acetone in order to. precipitate polyacrylamide. The precipitate was filtered, dried by desiccation. o Experiments have been carried out at 55 C in a thermostated bath. The total volume of reaction solution was 50 ml and initial acrylamide concentration was 0.6 M. Except EDTA which was studied at 2xl0~2 M and 4xl0~2 M, the other polyaminocarboxylic acids, NTA, DTPA, EGTA were studied at 2x10 M concentration. Initial Cerium (IV) sulfate concentration was in the range of 0.05-1.0 M. The length of reaction was 60 minutes. The effect of polyaminocarboxylic acid and Ce(IV) concentration, polymerization time and H SO concentration on the polymerization yield and molecular weight of polyacrylamide was studied. Polymers except EGTA, do not dissolve in water and probably make cross-link because of their high moleculer weight. From the curves of Ce(IV) concentration effect on polymer yield, shows that Ce(IV) concentration and the yield are proportional. By using low acid concentration, soluble polyacrylamide has been obtained which has a low molecular weight. The results of the effect of sulfuric acid concentration changes on the yield, agrees with the chance of formation of Ce ( IV ) sulfate complexes. At low sulfate concentrations formation of more active Cerium (IV) sulfate complexes also serve the termination of polymerization by Ce(IV) instead of mutual termination.