Redoks yöntemi ile dietil malonat ve L-aspartik akrilamid ile polimerizasyonu

Abstract

Seryum(IV) sülfat, çak hızlı elektron transferi ya pabilen oldukça kuvvetli yükseltgen bir maddedir ve bu özelliğinden yararlanılarak serbest radikal polimerizas- yonunda bir organik asit eşliğinde başlatıcı alarak kul lanılmıştır. Bu çalışma; iki temel bölümden oluşmuştur. I. Kimyasal yöntemle. ; Akrilamidin Malonik asit dietilesteri ve L-aspartik asit ile kimyasal (elektroli tik olmıyan) yöntem ile yapılan serbest radikal polimeri- zasyonunda başlatıcı olarak Seryum (IV) kullanılmıştır. Bu koşullar doğrultusunda, çeşitli ortam şartlarında deneyler yapılmıştır. Bu yöntemde kullanılan Seryum(IV) miktarını rejenere edilememiştir. II. Elektrolitik yöntemle ise/aynı maddelerle yapı lan serbest radikal polimerizasyonunda başlatıcı olarak kullanılan Seryum(IV) ün Seryum (III) 'e indirgendikten sonra aynı ortamda elektroliz ile tekrar Seryum ( IV) ' e yükseltgenebilmesi ve yeniden kullanılabilmesi için gerek li olan elektroliz koşulları ve kullanılabilecek en uy gun elektrotların neler alabileceği araştırılmıştır. Bu amaçla; yapılan deneylerde, ürün verimine (poli- mer miktarına ve molekül ağırlığına), sıcaklığın elekt roliz süresinin, Seryum (IV), malonik asit dietil esteri, L-aspartik asit konsantrasyonlarının, akım yoğunluğunun, elektrot potansiyelinin ve kullanılan çeşitli elektrotla rın (çelik, kurşun, Cr-Ni, grafit gibi) etkileri ayrı ayrı incelenmiştir. Sanuç olarak; Düşük Seryum(IV) konsantrasyonlarında (ix1G mol/1 elektrolitik yöntemle ve grafit elektrotlar kullanılarak elde edilen ürün miktarı, aynı şartlarla elektrolitik olmıyan yöntemle elde edilen ürün miktarın dan daha fazla bulunmuştur, ve daha düşük (1 x1 D" mol/lt) Seryum(IV) konsantrasyonunda kimyasal yöntemle polimer elde edilmezken, aynı konsantrasyonda elektrolizle yapı lan deneylerde polimer elde edilmiştir. Kullanılan elektrotlardan en yüksek verim grafit elektrotla elde edilmiştir. Ayrıca; kimyasal yöntem ile çalışmalarda, düşük Seryum(IV) konsantrasyonunda verimin düştüğü, sıcak lık ve konsantrasyonun artmasıyle verimin arttığı gözlen miştir. Reaksiyon süresinin arttırılmasıyla da polimer veriminde artış görülmüştür.

Free radical chain polymerizations and specifically acrylamide polymerization most important polymerization method as far as their industrial utilization is concerned, The propagating site 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 site is reformed on the newly fixed Last Unit of the chain. Substituted acrylamides and metacrylamides having the general formula I ! ! cdnr'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 same nitrogen compounds VI (form-amide, molten urea). Ce(IV) salts-reducing agent systems are well known initiators for vinyl polymerization, especially for graft copolymerization af vinyl monomer such as acrylonitrile and acrylamide. 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; polymerization of acrylamide was carried out with Ce(IV) L-Aspartic acid and diethly malonate redox initiator system with and without electrolysis. The effect of temperature, time, Cerium(IV) and Organic compounds molecular weight were studied and compared with electrolytic conditions. At low concentrations of Cerium(IV) the electrolytic method has an advantage of supplying Ce(IV) continuously over the nonelectrolytic conditions Cerium(I\/) oxidation of organic compound to Ce(III) while reduces Ce(IV) produces transient free-radical species which is capable of initiating vinyl polymerization. In this study, the Ce (IV) *- L-Aspartic acid and the Ce (IV) -diethly malonate redox systems was used to initiate the polymerization of acrylamide. The effects of temperature, time, Ce(IV) concentrations on the polymeriza tion yield and molecular weight were studied and compared with the results obtained under the same experimental conditions in the presence of electrolysis. Ceric sulfate Ce(S0,)2. ^HLO, (Merck, p. a), Aspartic Acid (Merck, p. a). Diethly malonate (Fluka, puriss). Acrylamide and sulfuric acid were all Merck reagent grade chemicals of the highest purity. Acetone was provided from Turkish-Shell company, (in Technical grade) Vll Polymerization was carried out in a three necked flask. Aqueous solution of acrylamide and amino acid were addsd into the flask and stirred with magnetic stirrer. Cerium(IV) salt solution was added dropwise in 6.7 minutes and the polymerization was finished, solution was left at room temperature. This solution was precipitated with a large amount of acetone by adding that solution dropwise into the acetone. This precipitate was filtered and dried under vacuum at room temperature in 5 hours to 3 days. Polymerization reactions have been carried out at 55 C in a thermostated bath for 1 hour. The total volume of reaction solution was 1 DO ml and initial acrylamide concentration was 0.3 M. L-Aspartic Acid and diethly malonate concentration was 2x10 M. The effects of amino acid, Cerium(IU) concentration, time, temperature 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 ostwald viscometer. In water at 25 C, the relationship of equation being used as following. [n] = 6. BO x10-4MD-66 * h The more significant result is that there is no polymerization at concentrations below 4x1 0~ M eerie sulfate in the absence of electrolysis on the other hand if there exists electrolysis. -Polymerization occurs at concentrations below 4x10~ M eerie sulfate, even at 1x10 M eerie sulfate. The molecular weights of the polymers which obtained with electrolysis systems, also shgwed a sharp increase at concentrations below 4x10 mole /l Ce(IV), these results are presumed to be related Vlll to the termination reaction by the recombination of polymer radicals, rather than termination with cerium(I\/) where cerium (III) concentration is relatively low. In this study, it seemed that the effect of the type of electrode an the polymer yield was vital. In all of these experiments three types of electrodes are used They are steel, Cr-Ni and graphite electrodes. The results of experiements showed that graphite was the best electrode among other metal electrodes that are used, concerning with the yield. The effect of the polymerization temperature and different concentrations of Ce(IV), L- aspartic Acid and diethly malonate concentrations under the same experimental conditions with and without electrolysis, at three different temperatures and eight different concentrations were studied. Conclusion, all of these results show that the electrolytic method has an advantage over the nonalectrolytic method at, very low concentrations of cerium(I\/) (at 1x10" mole/1) which can be continously regenerated during the electrolytic process. All of these studies and previous studies support the following reaction mechanism, which is given in Scheme I and II.