Ce (IV) poliaminokarboksilli asit başlatıcı poliakrilamidlerin sentezi ve karakterizasyonu
The Synthesis and characterization of polyacrylamides initiated by Ce (IV) polyaminocarboxylic acids
- Tez No: 46132
- Danışmanlar: PROF.DR. A. SEZAİ SARAÇ
- Tez Türü: Yüksek Lisans
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 68
Özet
ÖZET Bu çalışmada, seryum(IV) sülfat ve seryum(IV) amonyum nitrat - NTA (nitrilotriasetik asit), EDTA (Etilendiamintetraasetik asit), DTPA (Dietilentriamin pentaasetik asit) ve CDTA (1,2 siklohegzondinitriletetraasetik asit) ile başlatılmış poliakrilamid polimerizasyonu sulu sülfürik ve nitrik asit ortamlarında gerçekleşti rilmiştir. Asit ve seryum iyonlarının konsantrasyon etkisi, anyon türünün polimeri- zasyon verimi, sonlarıma mekanizması ve zincir yapısındaki etkisi gravimetrik, spektrofotometrik (FT-IR ve UV), kondüktometrik olarak incelenmiştir. Elde edilen polimerlerin yapısı, çözünen ve çözünmeyen olarak iki kısımdan oluşmaktadır. Bu iki kısım için kompleks yapılan incelenmiştir. Deneysel sonuçlan Ce(III) ile sülfat ve nitrat iyonlan arasındaki kompleks yapısının, reaksiyondaki değişik reaktivitelere sahip Ce(S04)nx(+ veya _) ve Ce(N03)nx(+veya“), türleri şeklinde olduğunu göstermiştir. Polimerlerin FT-IR ve UV spektrumlanyla birlikte kondüktometrik ve gravimetrik ölçümleri, Ce(III) sülfat kompleksleri durumunda, komplekslerin sadece uç grupta değil, aynı zamanda zincirdeki amid gruplarında da olduğunu göstermiştir. Bu çalışmada kullanılan redoks çiftleri arasında üretilen primer radikallerinin kararlılığının anyon türüne, asit konsantrasyonuna ve yükseltgen maddeye bağlılığı gözlenmiştir. Buna göre: - Sülfat komplekslerinin, nitrat komplekslerinden daha etkili sonlandıncılar olduğu, - Ce(TV) ve N03”koordinasyon kabiliyetinin, S04= 'tan daha zayıf olduğu, - Ce(IH) iyonu ve akrilamidin amid gruplan arasındaki kompleks oluşumu nedeniyle hem monomer hem de poliakrilamid radikallerinin reâktivitesinde değişiklikler olduğu gözlenmiştir. ıx
Özet (Çeviri)
SUMMARY THE SYNTHESIS AND CHARACTERIZATION OF POLYACRYLAMIDES INITIATED BY Ce(IV)-POLYAMINOCARBOXYLIC ACIDS Aqueous polymerization of vinyl monomers initiated by redox systems involving metal ions in their higher valance states (Co3+, Ce4+, Cr6“1”, Mn3+, V5+.., etc.) coupled with various organic substrates were entensively studied. Ce(IV) salts are more efficient initiators than the others and frequently used for oxidation of many organic reducing agents. The well-known reaction between ceric(IV) salt and an organic reducing agent such as alcohols, glycols, aldehydes, ketons, acids, amides, carboxylic acids, hydrocarboxylic acids, amino acids and polyaminocarboxylic acids., etc. is a redox reaction. The effects of acid type and concentrations on the initation and termination steps of redox polymerization initiated by Ce(IV) reagents have been explained by various authors. The oxidation reduction produces cerous ions ad transient free radical species cabaple of initiating vinyl polymerization. The following scheme was generally proposed for Cerium(IV) organic reducing agent redox system Ce(IV) + R ^=* [Ce(IV)-R]compkx [Ce(TV)-R] - ^* R. + Ce(III) (decomposition) Primary radical R. + M * RM RM. + nM -±*> R(Mn)M Several termination possibilities reported depending on cerium(IV) concentrations and other factors. v R(Mn) + Ce(IV) -^ Polymer + Ce(III) + H+ (Termination by cerium(IV))R(Mn)M + M(Mn)R - ^ R-Mn-M-M-Mn-R (Mutual termination) It is known that when a reducing agent which have functional group is used, the same functional group may be present as an end group at the end of the polymer chain. Quantative determination of such functional groups is particularly difficult because of the extremely low level at which they exist in the polymer. However, such analysis may play an integral part in understanding the mechanism of polymer initiation and termination, and the role of the catalyst. Titrimetric and spectrophotometric methods for determining functional end groups are widely used for number avarage molecular weight measurements and other polymer characterization. Polyaminocarboxylic acids, commonly used as chelating agents, in the decontamination of living organism, end recently, as possible substitutes for phosphates in detergents, are known to form complexes with trivalent lanthanides. In these work, NTA (Nitrilotriacetic acid), DTP A (Diethylene triamine penta acetic acid), EDTA (Ethylene diamine penta acetic acid), CDTA (1,2-cyclohetane dinitrilo tetra acetic acid)-ceric sulfate and-ceric ammonium nitrate redox systems as initiator were used to initiate the polymerization of acrylamide. The effect of acid and eerie ion concentrations, and anion type on the polymerization yields, termination mechanism and chain structure were interpreted by means of gravimetry, FT-IR, UV and conductometry and compared with the results obtained by the same redox initiators under the similar experimental conditions. In this work, polymerizations were carried out in the presence of atmospheric oxygen. After polymerization, in order to free them from any residual monomer and initiator, aqueous solutions of the polymers which was precipitated in acetone were prepared. This process pointed out that they contain two different part: soluble and insoluble but swells in water. The molecular weights of soluble parts which were precipitated by pouring into acetone were low ( Mv =2000). The compositions and structures of these parts of the samples were investigated by spectroscopic methods and conductometric measurements while the insoluble ones containing crosslinks were used for analytical separations of various solutions containing different metal ions. From the comparison of FT-IR and UV spectra polymerization yields of both soluble and swelling parts of the samples, it is observed that stability of primary radicals which is generated by four polyaminocarboxylic acid-ceric sulfate redox pair in sulphuric acid media decrease in the order of NTA > DTPA > CDTA > EDTA 103 > 87 > 41 > 29 (yield in %) The bands attributed to cerous and sulfate ions (-1100 cm“1 and 500-700 cm”1) more stronger as the reactivity of chelating agents increased. But wave numbers of the peaks which are assigned to polyacrylamide do not show any change xidifferent samples because the polyaminocarboxylic acids which is used as an initiator have about the same absorption bands with the polymers. When eerie sulfate was used as an initiator, it was found there was no polymerization of the acrylamide even after 60 min. So we can say that the initiation occurs through primary radicals produced by the eerie sulfate-polyaminocarboxylic acids interaction. UV results, also supports the assumption that polyacrylamides synthesized by eerie sulfate-chelating agent redox systems mainly contain Ce(III) -sulfate groups, as their chelating ability decreased. Their absorption spectrum showed four or five maxima. The peaks at about 295 nm (small), 252 and 239 nm (strong bands) and a moderate one at 221 nm are effected by variations in the amounts of the eerie ions present in the chain structure. In all cases a strong absorption centered at 210 nm was assigned to amide groups in the polymers. As to our FT-IR and UV results which is obtained for soluble parts of the polymers, we can suggest that in this system, cerous sulfate complexes could form complex with the amide groups in the repeating units of the polymers, in addition to the termination by metal sulfate. So there are two different termination mechanism for growing polymeric radicals. Termination for the insoluble parts (because of their strong amide and metilen peaks) occurs mainly by mutual termination while the cerium is introduced into the polymer chain together with sulfate ions, for soluble ones (lineer termination). In the experimental conditions of this work, eerie sulfate and sulfuric acid concentrations are extremely high (0.03 mole/L and 0.75 M, respectively). Therefore, in the present system it can be suggested that the metal complexes such as Ce(S04)2, Ce(S04)32“ which is produced by highly concentrated solutions have an important influence in the termination steps of poly (AAm) radicals. On the other hand, polyaminocarboxylic acid-ceric ammonium nitrate redox pair in nitric acid media were studied, too. The gravimetric results shows that their chelating ability in 0.75 M nitric acid solution increase as follow: DTPA < EDTA < NTA < CDTA (98) < (89) < (59) < (5) (yield in %) In these systems, oxidant concentration also has an important effect on initiation and termination mechanism, together with acidity of solution. Both chelating ability and mutual termination reduce under the high eerie ammonium nitrate concentration because of increasing Ce(IV)-(NQ3)n complex formation. İt can be also seen that metal complexes having anions have influence upon polymerization mechanism, in comparison with gravimetric results and molecular weights of polymers synthesized with Ce(IV)-NTA redox pairs. Redox polymerization of acrylamide was carried out in the presence of eerie ammonium nitrate-NTA redox pair, and the dependence of the structure and termination mechanism on the atmospheric oxygen, temperature, concentrations of the monomer, oxidant, reductant and nitric acid were studied. The soluble products xiiobtained in aqueous nitric acid solutions in the presence of and without air gave FT- IR spectra that are quite sharp and closely resemble each other, both containing strong anion bands (N03”) at 1400 cm“1. The disappearance of this N03”band for aqueous solution containing no nitric acid indicates that the anion during the synthesis has a different effect on the regularity of the bands between amide groups of acrylamide units in the polymer, together with cerous ion. The most possible mechanism explaining of this effect is the formation of a complex between cerous ion and polymer. This absorption band at ~ 1400 cm“1, indicating the presence of anion incorporated in the polymer, also supports the assumption that the cerium is introduced into the polymer chain together with nitrate ion. The major difference between two eerie salts having different anion is that (in the case of eerie ammonium nitrate-NTA redox system) the molecular weight of the soluble parts is higher than that of the others. This could be due to one or more of the following: i) The sulfate complexes are more effective terminators than the nitrate complexes. ii) Coordinating ability of N03”with Ce(IV) is weaker than that of S04= iii) A change in the reactivity of both the monomer and poly (AAm) radicals by the formation of a complex between their amide group and cerous ions. This NTA-ceric ammonium nitrate redox pair's UV spectrum indicates that cerium is introduced only into the end group of polymer chain as a type such as cerous nitrate, because of its weak peak at 252 nm. This is expected to reduce the conductivity significantly, as is observed experimentally. The conductometric titration results for polyaminocarboxylic acids Cerium (IV) sulfate show these conductivity values in the beginning without the addition of titrant as follows: NTA < CDTA < EDTA < DTPA ~ 1400 ju-s < -2100 tıs < -2900 ^s < -3600 /*s Both FT-IR and UV spectra of the polymers, together with their conductometric measurements clearly show that sulfate cerate complexes reduce the polymerization ability of growing poly (AAm) and primary radicals which is generated by chelating agents. On the other hand, since the conductivity values in the case of CDTA, EDTA and DTPA is higher than that of NTA. We believe that for these three samples, there are complexes not only on the end group but also on amide groups within the chain. From the comparison of conductometric titration of eerie ammonium nitrate- NTA and eerie sulfate-NTA redox pairs, both titration proceeded within the same way and gave an FT-IR spectrum and conductivity curve nearly identical. But in the case of eerie ammonium nitrate-NTA redox pair conductivity value (- 1000 /*s) xiiibefore the titration was lower while the molecular weight was greater about ten-fold (~ 13.000). It means that cerium ion would be found present on the end groups of the polymer chains as a terminator agent. Therefore, conductivity values were inversely proportional with their molecular weights. The results thus lead the conclusion that the low conductivities observed for polyacrylamides initiated with NTA are related to the chelating ability of this reducing agent, acid concentration and anion type. Because increasing nitrate ion increased the chelating ability while sulfate anion reduced the complex stability of the Ce(TV)-NTA redox system. These observations suggest the presence of unknown relations and balances between the polymer and metal complexes and the role of the anion of the salts requires further investigation. xiv
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