Redoks polimerizasyon yöntemi ile aren uç gruplu poliakrilamid sentezi

Abstract

Seryum(IV) sülfat, çok hızlı elektron transferi yapabilen oldukça kuvvetli yükseltgen bir maddedir. Bu özelliğinden faydalanılarak serbest radikal polimerizas- yonunda bir aren eşliğinde başlatıcı olarak kullanılmıştır. Bu çalışmadaki amaç kimyasal ve elektrokimyasal rejenerasyonla akrilamidin aren ve Seryum(IV) başlatıcılı serbest radikal polimerizasyonunun incelenmesidir. Kullanılan arenler antrasen, fenantren, naftalin, asenaften, asenaftilen ve pirendir. Bu amaçla; yapılan deneylerde ürün verimine (polimer miktarına) zaman, sıcaklık, Seryum(IV), H2SO4. aren konsantrasyonlarının ve kullanılan çeşitli elektrotların etkisi incelenmiştir. Sonuç olarak; düşük seryum (IV) konsantrasyonlarında grafit elektrotlar kullanılarak elde edilen polimer miktarı, aynı şartlarda elektrolitik olmayan yöntemle elde edilen polimer miktarından daha az bulunmuştur. Yüksek Seryum(IV) konsantrasyonlarında ise grafit elektrotlar kullanılarak elde edilen polimer miktarı, aynı şartlarda elektrolitik olmayan yöntemle elde edilen polimer miktarından daha fazla bulunmuştur. Aren konsantrasyonu arttıkça elde edilen polimer miktarı azalmıştır.

The free radikal 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 peroxodisulf ate ^Hydroperoxides c) Peresters d) Aliphatic azocompounds 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 I *? 2R. VI 2. The actual initiation reaction R- + M > RM- Propagations This reaction is repeated hundreds to many thousands of timers for each chain formed, it can be written as RMn- + M ? RMn+ı- Terminations Growing radicals can react with each other in two different ways. 1. By recombination, a homopolar bond is formed by pairing the single electrons of the free radical sites of two chains s R - M"- + R-Mp- ? R - Mn + p 2. By disproportionation, where by a hydrogen atom is transferred form one chain to the other two molecules of "dead" polymer are formed. R - Mn- + R - MP <- R - Mn + R - Mp Acrylamide Polymers This study deals primarly with arcrylamide 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 molecular-weight polymers. Common initiators are peroxides, azo compounds, redox pairs, photochemical 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 peroxydisulf ate- bisulfite couple, and peroxide with ferrous ammonium sulfate. Ionizing radiation has been studied extensively VII 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. The mechanism of free radical polymerization of acrylamide has been studied extensively. At 25°C the rate constant is reported as. kp - 1.8x10* 1-mole-* -sec-1 for propagation kt - 1.45x10? 1-mole-1 -sec-* for termination kt« - 2.2X10-1 1-mole-1 -sec-1 for transfer The ratio kP/kt exceeds that reported for any other monomer, kp being exceptionaly high ant kt rather low. The redox reaction between Cerium (IV) Sulfate and organic reducing compound has been used for initiation of vinyl polymerization. The polymerization mechanism involves the generation of free radicals from the complex formed between Cerium (IV) salt and reducing agent following the formation of free radical which initiates the polymerization of vinyl monomer. In this work, polymerization of acrylamide was carried of with Cerium (IV) arene (anthracene, phenanthrene, naphthalene, acenaphthen, acennaphthylen and pyrene) redox initiator system with and without electrolysis. The effect of temperature, time. Cerium (IV) and arene molecular weight were studied and compared with and without electrolysis. The redox reaction between Cerium (IV) Sulfate and arene may be written as follows; VIII Arene + Ce(IV) ^-^ Complex e- i.. J. B ki Ce(III) + R. + Monomer where B is a base or nucleophilc Polymerization was carried out in a three necked flask. Aqueous solution of acryl amide and arene were added into the flask and the stirred with magnetic stirrer. Cerium(IV) salt solution was added dropwise in 10 minutes. After certain period of polymerization time, the content of the flask was poured into the acetone in order to precipitate polyacrylamide. This precipitate was filtered and dried under vacum at room temperature. Polymerization reactions have been carried out at 50°C in a thermostated bath for 2 hours. The total volume of reaction solution was 100 ml. and initial acrylamide concentration 0.5 H. Arene concentration Ixl0-2M. Initial Cerium (IV) Sulfate concentration was in the range of lxlO-3 - 4xl0~2M. The effect of arene, Cerium(IV) concentration, time, temperature and H2SO4 concentration on the polymerization yield and molecular weight of polyacrylamide was studied with and without electrolysis. The molecular weights of the polymers were determined by using on Oswald viscometer. In water at 25°C, the relationship of equation being used as following. ^] - 6.8 X 10- Mn( 66 IX The more significant result is that there is no polymerization at concentration below lxlO-3 M Cerium (IV) sulfate with and without electrolysis. At high cerium(IV) concentration the electrolytic method has an advantage of increasing polymer yield. It was observed that increasing Cerium(IV) concentration resulted an increase in both the yield and the molecular weight of polyacrylamide. From the curves of Cerium (IV) concentration effect on polymer yield, shows that Cerium (IV) concentration and yield are proportional. In this study, the effect of arene concentration on the polimerization yield was studied. It was obtained that lxlO-2M arenes concentration resulted a high polymer yield. The effect of the sulfuric acid concentration on the polymerization yield was studied. The change of the sulfuric acid concentration changes on the yield.