Akrilamidin potasyum permanganat titriplex VI redoks sistemi ile elektrokimyasal polimerizasyonu

Abstract

KMn04 çok hızlı elektron transferi yapabilen oldukça kuvvetli yükseltgen bir maddedir ve bu özelliğinden yararlanılarak serbest radikal polimerizasyonunda bir organik indirgen madde eşliğinde başlatıcı olarak kullanılmıştır. Bu çalışma: İki temel bölümden oluşmaktadır. I. Kimyasal Yöntem : Akrilamidin Titriplex VI(C14H24N2Oı0) ile kimyasal yöntem ile yapılan serbest radikal polimerizasyonunda başlatıcı olarak KMn04 kullanılmıştır. Bu koşullar doğrultusunda, çeşitli ortam şartlarında deneyler yapılmıştır. Bu yöntemde kullanılan Mn(III) ve Mn(II) miktarı tekrar rejenere edilememiştir. II. Elektrolitik Yöntem : Aynı maddelerle yapılan serbest radikal polimerizas yonunda başlatıcı olarak kullanılan Mn(VII)'nin Mn(IV), Mn(III) ve Mn(II)'ye indirgendikten sonra tekrar Mn(IV) ve genellikle Mn(III)'e yükseltgenebilmesi ve yeniden kullanılabilmesi için gerekli olan elektroliz koşulları ve kullanılabilecek en uygun elektrotların neler olabileceği araştırılmıştır. Bu amaçla; yapılan deneylerde ürün verimine (polimer miktarına ve molekül ağırlığına); sıcaklığın, monomer, KMn04, Titriplex VI konsantrasyonlarının, elektrot potansiyelinin, asit konsantrasyonunun ve kullanılan çeşitli elektrotların etkileri ayrı ayrı incelenmiştir. Sonuç olarak; kimyasal yöntemle polimerizasyonun en iyi gerçekleştiği koşullar; 50°C'de 0.3 M Akrilamid, 2.10`2 M Titriplex VI, 5.10`2 M KMn04 ve 0.25 M H2S04 ile gerçekleştirilmiş olup, dönüşüm yüzdesi % 83.5'dur. Elektrokimyasal yöntemle polimerizasyonun en iyi polimerizasyonun gerçekleştiği koşullar yine ay nı deney şartlarında olup; grafit elektrotlarla % 102 verim elde edilirken, platin elektrotlarla %77'lik bir verim elde edilmiştir.

Free radical chain polymerization and specially acrylamide is the most important polymerization 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 on 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. For example, an individual propagation of the polymerization of a vinyl monomer CH2=CHR can be schematized as : - CH, - CH. + CH, = CH I R R -CH, - CH - CH, R CH. I R Acrylamide, CH2 = CHCONH2, is the parent compound of a large class of monomers that includes methacrylamide CH2 = C(CH3)CONH2 and scores of N-substituted derivatives CH2 = CHCONR'R`. Polyacrylamide is available as a high molecular weight material that is soluble in water under nearly all conditions. Copolymers can be made easily with most other monomers, thus extending the range of properties and applications. Polymer derived from the substituted monomer includes clear gels, soft gums and hard plastics. Substituted acrylamide and methacrylamide having the general formula R CH, -C I CONR'R` yield polymers ranging from hard and brittle to soft and tacky.The well known reaction between permanganate and organic reducing agents, is known to involve free radical intermediates, has been employed as a free radical initiator of polymerization. In the aqueous polymerization of acrylamide initiated by permanganate- reducing agent redox system, it is thought that permanganate first reacts with acrylamide and produces immediately a brownish black solution, which interacts with reducing agent to produce free radicals (primary radicals) highly reactive Mn(III) ions. Mn(III) ions are supposed to be more reactive to produce free radicals (secondary radicals), which is capable of initiating the polymerization of acrylamide. Reaction mechanism is thought to be written as in Scheme I and II. In this work polymerization of acrylamide was carried out with potasyum permanganate- Titriplex VI (Ethylenedioxybis (ethylenenitrilo) tetraacetic acid, EGTA) redox initiator system with and without electrolysis. The effect of potassium permanganate concentration, acrylamide concentration and temperature on the polymerization yield was studied and molecular weights of polymer determined and compared with the results obtained under the same experimental conditions as in the case of electrolylsis. Acrylamide and sulfuric acid are all Merck reagent grade chemicals of the highest purity and without further purification. The polymerization was carried out in a three-necked flask equipped with a stirrer and funnel for the addition of permanganate solution, in a thermostated water bath from 20°C to 60°C for 30 minutes. KMn04 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 2-5 days. Polymerization reactions have been carried out in a thermostated water bath for 30 minutes. The total volume of reaction solution was 100 ml and initial acrylamide concentration was 0,3 M, Titriplex VI concentration was 2.10`2 M. The molecular weights of polymer was also determined by using Ubbelohde viscometer. In water at 30°C, the relationship of equation being used is given as following. [.n] = 68 x 10-3. M*-66 The molecular weights of polymers were also studied and compared with electrolytic conditions. The molecular weight of polymers obtained by the electrolytic method is lower than by the nonelectrolytic method. The reason for that may be the increase in the number of radicals under electrolytic conditions which results from the presence of the high concentration of Mn(III) obtained by recycling.At 5. 10`2 mol/1 concentration of permanganate, in the presence of electrolysis gave much higher conversion is about % 102 with graphite electrodes, in the absence of electrolysis conversion is about % 83.5. In the absence of potassium permanganate, there was no polymerization under experimental conditions with and without electrolysis but in the absence of reducing agent (Titriplex VI) there was polymerization under experimental conditions with and without eletrolysis. In the absence of organic reducing agent (Titriplex VI) polymerization proceeded under experimental (Ethylenedioxybis (ethylenenitrilo)tetraacetic acid, there was polymerization under experimental conditions with and without electrolysis. At 5.102 mol/1 concentration of potassium permanganate and 0.25 mol/1 concentration of H2S04 in the presence of electrolysis gave much higher conversion is about % 133, in the absence of electrolysis conversion is about % 11. The reaction mechanism is thought that direct oxidation of monomer by metal ion is the reduction of metal ion by solvent in terms of reaction. H20 H20 Mn4-± - >Mn3+ + H+ + OH - >Mn2+ + H+ + OH OH + M - > initiation of polymerization M : Monomer In this study, it seemed that the effect of the type of electrode on the polymer yield was vital. In all of these experiments three types of electrodes are used. They are graphite, platinium and Cr-Ni electrodes. The results of experiments showed that graphite was the best electrode among other metal electrodes that are used, concerning with the yield. In the experiments done with the Cr-Ni electrodes, the yield of the product which was red- brown in colour was low, because of this reason no more experiments with these Cr-Ni electrodes could be done. It is thought that the functional groups in the polymer produce a complex with one of the elements present in the Cr-Ni electrode causes this red-brown colour. It is easily seen that the structure of the polymer that is produced by platinium electrodes is more flexible and has more pores, while the one which is produced by graphite electrode has pores smaller in volume. Also the polymer that is produced by graphite electrodes is fiber in structure. These results were supported by scanning electron microscope (SEM). The effect of temperature on the yield was examined at six different temperatures under the same experimental conditions with and without electrolysis. A sharp increase was obtained at 50°C by both methods and electrolytic conditions showed higher yields at all temperatures.The effect of temperature on the yield was examined at six different temperatures under the same experimental conditions with and without electrolysis. A sharp increase was obtained at 50°C by both methods and electrolytic conditions showed higher yields at all temperatures. FT-IR spectra of Titriplex VI-KMn04 initiated polymerization show characteristic peaks of both polyacrylamide and carboxylic acid at about 1420 and 1650 cm`1. All of these studies and previous studies support the following reaction mechanism, which is given in Scheme I and II. 0 O OH £ kN~°N'/>~N>l HO, J ^C jr ° oh o Scheme I. Organic Reducing Agent.OH OH I I Acrylamide + 2KMn04 +H2S04- >H - C - C - H + K2S04 + Mn(IV) I I H C = O I NH, Mn(IV) -f Organic Reducing Agent^± [Mn(III)-reducing agent] [complex] Mn(III) f R CH (OH) + H+ + C02 (L,.) Mn(III)f RCH(OH)COOH- ^Mn(II) + RC(OH)COOH + H+ (L2O initiation U- + CH2 = CH-^> Lz - CH2 - CH. I I c = O c = o I I NH2 NH2 Propagation : L - AM. + nAM-^L-(AM)n - AM. Termination : a) L - (AM)n - AM. + L - (AM)m - AM^->L- (AM)n+1 - (AM)m+1 - L b) L - (AM)n - AM. + Mn(III)->L - (AM)n - AM - Mn(II) + H+ Regeneration Mn(III) species electrolytically e` Mn(II) -> Mn(III) Scheme II. Polymerization of Acrylamide with Potassium Permanganate Reaction Mechanism.