Seryum (IV) ve permanganat başlatıcısı ile bazı hidroksi asitler ve difenileterin akrilamid polimerizasyonu

Abstract

Seryum (TV) sülfat ve potasyum permanganat çok hisli elektron transferi yapabilen maddeler olduklarından organik bir indirgen madde ile serbest radikal polimerisasyommda baslatıcı olarak kullanılabilmektedir. Bu çalışmada öncelikle indirgen madde olarak sitrikasit ve difenil eter'in Seryum (İV) ve potasyum permanganat ile serbest radikal polimerisasyonu karşılaştırmalı olarak incelenmiş, ayrıca malonik asit ve tartarik asidin potasyum permanganat ile polimerisasyonu değişik şartlarda incelenmiştir. Sitrik asit ile yapılan deneylerde Akrilamid'in sitrik asit vasıtasıyla Seryum (IV) ve potasyum permanganat baslatıcı lar ı ile polimerisasyonu çeşitli ortam şartlarında kimyasal ve elektrokimyasal olarak incelenmiştir. Difenil eter ile yapılan deneyler akrilamid'in bir aromatik eter olan difenil eter vasıtasıyla serbest radikal polimerisasyonu Seryum (IV) ve potasyum permanganat başlatıcılarıyla gerçekleştirilmiştir. Malonik asit ve tartarik asit ile yapılan deneyler ise yalnısca potasyum permanganat kullanılmıştır. Yapılan deneyler kimyasal ve elektrokimyasal polimerisasyon koşullarında gerçekleştirilmiştir. Deneyler sonucunda elde edilen polimerlerin verimi Seryum (IV) ve potasyum permanganat konsantrasyonu ve sıcaklıkla değişiminin etkisi kimyasal ve elektrokimyasal yöntemlerle karşılaştırmalı olarak gerçekleştirilmiştir. Sonuç olarak artan baslatıcı konsantrasyonları gösönüne alınarak kimyasal ve elektrokimyasal yöntemde ürün verimi artış göstermiştir. Ayrıca düşük baslatıcı konsantrasyonlarında kimyasal yöntemle polimerler elde edilemezken, grafit elektrotlar kullanılarak yapılan denemelerde ürün elde edilmiştir.

Free radical chain polymerisations have become the most important method as far as their utilisation is concerned. The propagating site is a free radical, an impaired electron at the last carbon atom of the growing chain. A free radical polymerisation thus involves many successive steps of growth. In each of them a monomer molecule is added to the chain, where by the radical side is reformed on the newly fixed last unit of the chain. For example, an individual propagation of the polymerisation of a vinyl monomer CHs = CHR can be schematised as : CH2 - CH-+ CHs = CH I I R R -* - CHz CH - CHs - CH- I ! R R Acrylamide, CHs = CHCONHs, is the parent compound of a large class of monomers that includes methacrylamide, CHs = C(CH3)C0NHs and scores of N-substituted derivatives CHs = ChCONR'R". Polyacrylamide is avilable 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. Polymers derived from the substituted monomer include clear gels, soft gums and hard plastics. Substituted acrylamides and methacrylamides having the general formula. CHs C CONR'R" n v** Ce(IV) salts-reducing agent systems in aqueous acidic solution are uses as initiators of vinyl polymerisation. The well-known reaction between Ceric(IV) salt and organic reducing agent such as alcohol, glycol, aldehyde, ketone and carbcxylic acid is a redox reaction- The oxidation - reduction produces cerous ions and transient free radical species capable of initiating vinyl polymerisation. Recently, the aqueous polymerisation of acrylamide by the permanganate - reducing agent system (such as lactic acid glyceric acid) has been investigated. In the aqueous polymerisation of acrylamide initiated by permanganate - reducing agent redox system, it is thought that, permanganate first reacts with acrlamide and produces immediately a brownish black solution, which interacts with reducing agent to produce free radicals (primary radicals) higly reactive Mn(III) ions. Mn(III) ions are supposed to be more reactive to produce free radicals ( secondry radicals ), which is capable of initiating the polymerisation of acrylamide. Reaction mechanism is thought to be written as Scheme I. Tn this work, polymerisation of acrylamide was carried out with Ce(IV) - citric acid and diphenyl ether redox initiator system with and without electrolysis. Polymerisation of acrylamide was also carried out with permanganate - reducing agent (citric acid, malonic acid, tartaric acid and diphenyl ether) redox initiator system with and without electrolysis. The effect of temperature Cerium (IV) and permanganate concentrations studied and compared with electrolytic conditions. At low concentrations of Ce(IV) the electrolytic method has an aduantage of supplying C-e(IV) continiously over the nonelectrolytic conditions Ce(IV) oxidation of organic compound to Ce(III). At low KMnCU concentrations, polymerisation did not occur in the absence of electrolysis. Ceric sulfate (Merck) KMnCU (Merck) Citric Acid (Merck) Tartaric Acid (Merck) Malonic Acid (Merck) Diphenyl Ether (Merck) Acetonitril (Merck) Acrylamide and sulfuric acid were all Merck reagent grade chemicals of the highest purities. Acetone was provided from Aygas Company. vi 1 1 Polymerization was carried out in a three necked flask. Aqueous solution of acrylamide and amino acid were added into the flask and stirred with magnetic stirrer. Cerium (IV) and KMnCU 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 100 ml and initial acrylamide concentration was 0.3 M. Citric Acid, Malonic Acid, Tartaric Acid an d diphenyl ether concentration was 2xl0_2M. The effects of reducing agents, Cerium(IV) and KMnC-4 concentration, time, temperature on the polymerization yield and molecular weight of poly acrylamide as studied with and without electrolysis. The molecular weights of the polymers were determined by using on Ostwald viscometer. In water at 30 °C, the relationship of equation being used as f o lowing. -4 o.ee [*] = 6.80x10 Mn While Ce(IV) is used in polymerization reactions, IxlO-4 M is enough to initiate the polymerisation. When IxlQ-3 M KMnQ-4 as initiator polymerisation occur in the presence of electrolysis. Reaction results shows that when initiator concentration is increased, ratio of conversion to polymer increases. All the electrochemical experiments was carried out by using graphite electrodes. Scheme I, II, III show reaction mechanism. Jx Ce(IV)+HLH Complex [Ce - Reducing agent] Anodic Oxidation Ce(III)+HL.+H" I k± R. + CHa = CH -* R - CHa - 0 = 0 I &H2 (Akrilamid) CH I C = 0 I te2 Initiation (R - AM- ) R-AM- + nAM ?* R - (AM)» - AM. k* R-(AM)xx-(AM. )+R-(AM)«-(AM« ) Propagation -> R-CAMn*i)-(AM)m-H1-R Termination SCHEME I. Polymerization of Acrylamide With Ce(IV) Reaction Mechanism. HL-.R- OH OH I I Acrylamide + 2KMn04+ H2SO4 > 2MnOs + H-Ö - C -H + K2SO4 I I H 0=0 I Slow Mn(IV) + R - CH(OH) v * CMn(III) - reducing agent] > \ COOH Complex Mn(III) + R - CH(OH) + H + COs Slow, ^ Mn(III) + RCH(0H)C00H > Mn(II) + RC(0H)C00H + H k± R? + CHs = CH > R - CHs - CH 0 = 0 0 = 0 NHs NH R - AM* + 11AM > R - (AM)n - AM- Propagation k-c R- (AM)n-(AM«) +R(AM)m- (AM-) > R -(AM)n--ı- (AMWi- R Polymer Termination R. : Tartaric acid, malonic acid and citric acid radicals. SCHEME II. Polymerisation of Acrylamide With Potassium Permanganate Reaction Mechanism. Xi O OH O \\. ı // Citric Acid : C - CH - C - CH2 - C 7 l X HO 6 OH // \ O OH O H O W. I // Tartaric Acid : C - C - C - C / I I \ HO ÖH ÖH OH O O \\. // Ma Ionic Acid : C - CH - C / \ HO OH SCHEME III. Acid Radicals.