Poliaminokarboksilli asit Ce(IV) redoks sistemleriyle polimerleştirilmiş poli(metil metakrilat)ların karakterizasyonu
Başlık çevirisi mevcut değil.
- Tez No: 46162
- Danışmanlar: DOÇ.DR. CANDAN ERBİL
- 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: 77
Özet
ÖZET Alkoller, aminler ve karboksilli asitler gibi redüktan maddelerin Ce(TV), V(V), Co(III) ve Mn(III) tuzlan gibi oksidan maddelerle oluşturdukları redoks çiftleri sulu ortamda vinil polimerizasyonunu başlatabilirler. Polimerizasyon sonunda, indirgen maddeleri uç grup olarak içeren zincirler oluşur. Bu çalışmada, Ce(IV) ile dört farklı, şelat yapıcı özellikleri olan (NTA, HEDTA, DTPA ve CDTA) poliaminokarboksilli asidin ayrı ayrı oluşturdukları redoks katalizör sistemlerinin kullanılmasıyla, sulu ordamdaki metil metakrilat (MMA) polimerizasyonu incelenmiştir. Katalizör, gün ışığı ve havadaki oksijenin, molekül ağırlığı, molekül ağırlığı dağılımı ve verim üzerindeki etkilerini incelemek için gravimetrik, viskozimetrik, spektrofotometrik ve dielektrik ölçüm sonuçlan kullanılmıştır. Sentezlenen poli(metil metakrilat) lardaki (PMMA) -3425 cm1 'deki N-H gerilme titreşim, -2600 ve ~ 1620 cm“1 'deki amin ve - 1400 cm”1 'deki N03" bandlan ve asetondaki çözeltilerinin ~ 327 nm'deki Ce(IH) pikleri ile birlikte, jel geçirgenlik kromatografisi ve elde edilen yüksek dipol moment sonuçlan, çok farklı zincir uzunluklanna sahip ve yapısında peroksi bağlan içeren polimerler eldelendiğini ve üç farklı sonlanma mekanizmasının birden yürüdüğünü gösterdi. Kullanılan poliaminokarboksilli asitlerin polimerizasyonlan başlatma aşamasında, Ce(IV) ile kompleks oluşturma etkinlikleri ise (CDTA > DTPA > HEDTA > NTA) daha önceki çalışmalarla paralel idi. vm
Özet (Çeviri)
SUMMARY CHARACTERIZATION OF POLY(METHYL METHACRYLATE)S AS POLYMERIZED BY USING POLYAMINOCARBOXYLIC ACIDS-Ce(IV) REDOX SYSTEMS Redox polymerizations are initiated by the transient free-radical species produced by the reaction taking place between an oxidizing agent called catalyst or initiator and a reducing agent called activator. Redox polymerizations have very short induction periods, they can be carried out at low temperatures since their activation energies are much lower than thermally initiated polymerizations and they provide production of high-molecular-weight-polymers with high yields in a short time. In addition, polymers with functional end-grups can be obtained by redox polymerizations. The initiation step in the redox polymerization may be represented as follows: Oxidant + Reductant > R. + Products ki R. + M -î- > R - M. Here, k,. is the rate constant of the redox reaction. The rate of polymerization (Rp) and the degree of polymerization ( Pn ) are given as follows: p dt l 2fcfc+2^ 10.5 [Oxidant]05 [Reductant]05 [M] P = kp[M]“ pJc^+kjf5 [Oxidant]05 [Reductant]0' Here, k,,. is the rate constant for termination by combination and k^ is the rate constant for termination by disproportination. The factors that have important effects on Rp and Pn are the concentration of the monomer, the oxidizing and reducing agents, temperature, pH of the medium IXand the structure of the monomer. In general, an increase in the monomer concentration leads an increase in Rp and Pn. The oxidant is of 0.5 order in many redox systems. This value points out a bimolecular termination. If the order of the oxidant has a value between 0.5 and 1.0, the bimolecular termination changes to unimolecular termination which is the termination of the polymer chains by any kind of impurity or by dissolved metal ions present in the reaction medium. When the order is lower than 0.5, primary radical termination takes place. An increase in the temperature of the reaction medium results in an increase in Rp. pH can change Rp either by increasing the coagulation tendency of the diffused phase or by affecting the initiation rate. The structural properties such as polymerization ability, the order of the double bounds, the number of substituents and solubility of vinyl monomers are also important factors that affect Rp and Pn. In redox polymerizations, a proper choice of the oxidizing and reducing agents should be provided for an efficient initiation. The metal ions in their valance states such as Co(III), Cr(VI), Mn(III), Fe(II), and V(V) are commonly used oxidizing agents. Ce(IV) salts or Ce(IV) -reducing agent systems in aqueous acidic solution are also used in initiation of vinyl polymerization. Aqueous solutions of eerie perchlorate, nitrate, and sulfate in their respective acids initiate vinyl polymerization in the dark and at room temperature, and also photochemically. The initial rate of polymerization decreases in the order of eerie perchlorate > eerie nitrate > eerie sulfate. The oxidation of the organic compounds by eerie salts are found to follow different mechanisms depending on the type of acid media. In nitric acid, the higher the acid concentration the higher the rate. The average- molecular weights decrease as the acid concentration increases. The well known reaction between Ce(IV) salt and an organic reducing agent such as alcohol, glycol, aldehyde, ketone and carboxylic acid is a redox reaction. The most important feature of oxidation with the eerie ion is that it proceeds via a single-electron transfer with the formation of free radicals on the reducing agent. The reducing agent of eerie ion may be a polyaminocarboxylic acid. In these systems, Ce(IV) ions are known to form a complex with polyaminocarboxylic acids and this complex acts as a source of free radicals which initiates polymer formation. The mechanism of the redox initations may be represented as follows: Ce(TV) + R JLs (Ce(IV) - R) Complex (Ce(IV)-R) - > R. + Ce(IH) + H+ Complex where R and R. are the chelating agent and the initiator fragment radical, respectively. The k,, of the chelating type redox initiators is about 10-100 fold to the uusal initiators. The more the number of chelating rings; the larger the k,,. With this respect, the oxidations of certain polyaminocarboxylic acids in sulfuric acid and perchloric acid solutions were studied, and the rates of reduction of Ce(IV) by the four chelating agents were found to decrease in the order of CDTA > EDTA > DTPA > NTA.In the polymerization reactions initiated by Ce(TV)-polyaminocarboxylic acid redox systems, such monomers that perform heterogeneous polymerization as acrylonitrile, methyl methacrylate, methyl acrylate and styrene and such monomers that perform homogeneous polymerizations as acrylamide are used. In the studies of acrylamide polymerization initiated by Ce(IV)-EDTA redox systems, the yields and molecular weight of the polymers were found to be proportional to the Ce(TV) concentration at low initiator concentrations whereas H+ concentrations were found to be inversely proportional to the yields. The initiation step of the aqueous polymerization of MMA is a homogeneous process. Each primary radical generated in the redox reaction is added to the monomer molecule dissolved in the aqueous phase and then begins to propagate. With the growth of a polymer chain, some critical chain size is reached at which the higher-molecular-weight-chains are terminated by either cerium or initiator radicals and precipitated out. At this point, the polymerization begins to follow heterogeneous solution kinetics. Another termination process is the mutual termination. The polymer chain radicals combine and form a polymer molecule which precipitates. It is known that light, heat and air are effective agents for inducing the polymerization of certain vinyl compounds. Among these, oxygen exhibits both a catalytic and an inhibiting effect on the polymerization. The mechanism of the catalytic action of oxygen is undoubtedly related to peroxide formation. It is combined oxygen rather than oxygen itself which catalyses the polymerization. The inhibiting action of oxygen in photopolymerization is also related to the peroxide formation. The peroxide formation occurs in preference to polymerization in accordance with the following scheme M + UVL -» M* M* + 02 -» M02 (preferred reaction) M* + M ?* MM* -* MMM', etc. where M represents the unactivated monomer molecule; M*, the active center and M02, a peroxide. The catalytic activity of the peroxide is due to its tendency to generate M*, or similar active center, and these active centers exhibit the same preferential reactivity with oxygen as those formed by the action of ultraviolet light. In this work, aqueous polymerization of MMA initiated by Ce(TV)-NTA, - HEDTA, -DTPA and -CDTA redox systems was studied. Polymerizations were carried out in the presence of atmospheric oxygen and in the dark. Acidic aqueous solution of MMA and chelating agent were placed in a thermostated bath maintained at 35 °C or 55 °C. Polymerization was initiated by dropwise addition of eerie salt. After one hour, precipitated polymer was filtrated, washed with water, dried in vacuo and weighed. XIThe effect of daylight, oxygen, temperature, initiator, volume of the polymerization solution, concentrations of the monomer, acid and eerie salt on the yield and molecular weight of PMMA were studied. In addition, a comparison of PMMAs initiated by two different eerie salts, eerie ammonium nitrate and eerie sulfate, and characterization of PMMAs initiated by Ce(IV)-NTA and -HEDTA redox systems were in the concern of this work. First, blank reactions were carried out in order to test whether Ce(TV) alone could initiate the polymerization at 35 °C and the following eerie salt, acid and monomer concentrations: [Ceric ammonium nitrate]=2.88xl0”2 mol/L, [HNO3]=0.64 mol/L, and [MMA]=0.38 mol/L. Under these conditions, it was found that there was no polymerization of MMA even after 60 minutes, when ceric ammonium nitrate alone was used as an initiator, but with Ce(IV)- polyaminocarboxylic acids redox initiators, it was noticed that the polymerization reaction proceeded without any induction period. The fact that the polymers obtained by the polymerizations carried out in the presence of oxygen and daylight had higher molecular weights and yields than polymers obtained in the presence of nitrogen and in the dark showed that oxygen and light increased the rate of polymerization. The Ce(III) peak observed at 327 nm in the UV spectrum of PMMA in acetone, synthesized in the presence of oxygen pointed out that termination by Ce(HI) took place at an important level in the presence of oxygen and this caused formation of polymers with different molecule sizes. The polymerization reactions were carried out at two different temperatures. 35 °C for NTA and HEDTA, and 55 °C for DTPA and CDTA were found to be proper temperatures for the yield. The reactivities of the four polyaminocarboxylic acids in nitric acid medium was studied and it was observed that the reactivities of the chelating agents decreased in the order of CDTA > DTPA > HEDTA > NTA.' This order is parallel to the order followed in the literature. When the MMA concentration was increased, an increase in yield and molecular weight was observed. Decreasing the pH of the medium caused a decrease in yield and molecular weight. In the studies where the concentration of ceric ammonium nitrate was increased at low MMA concentrations, instead of combining with NTA to form a radical, the excess Ce(IV) was found to undergo an oxidation reaction with the initiator, thus forming an amino acid derivative containing metal ions which is not water soluble as an undesirable by-product. An increase in the volume of the reaction solution didn't change the yield at high MMA concentration, but by increasing the volume 3 times, a ~ 60% increase in the yield was observed at low MMA concentration. xnSpectrophotometric, viscosimetric and dipole moment methods were applied in order to characterize PMMAs initiated by Ce(TV)-NTA and -HEDTA redox systems. In FT-IR spectra of the polymers, characteristic peaks of PMMA at 1000- 1300 cm“1 for the esther group, at ~ 1730 cm”1 for the carbonyl group, and at 2800- 3000 cm*1 and 1350-1550 cm“1 for -CH3 and -CH2 streching and bending vibrations were observed. In addition to that, N-H streching vibration at -3425 cm”1, N-H bending vibration at - 1620 cm“1, amine peaks at about 2600 and 1620 cm”1 all of which belongs to the polyaminocarboxylic acids used as the initiator of our polymerizations were observed. From GPC chromatograms, it was found that the polymers which had heterogeneous structure were obtained as a result of the peroxide formation, oligomeric chains, oxidative termination by Ce(TV), termination by ligand transfer and mutual termination mechanism taking place during the polymerizations. The instability and high results observed in the dipole moment studies was a measure of both the peroxy bonds that create mobility in the chain and the heterogenity in the structure. xm
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