Azo bağı içeren politetrahidrofuran sentezi ve karakterizasyonu
Synthesis and characterization of azo-linked polytetrahydrofuran
Yazar: GÜRKAN HIZAL
Danışman: DOÇ. DR. YUSUF YAĞCI
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü
Derece: Doktora, 1988
Konu: Kimya = Chemistry
Dizin: Kopolimerler = Copolymers ; Politetrahidrofuran = Polytetrahydrofuran

Özet:
}IET Bu çalışmada yumuşak palieter zinciri (soft segment) içeren blok kapolimerlerin eldesi için yeni bir yöntem geliştirilmiştir. Bu amaçla tetrahidrofuranın azo bağı içeren bir diosit klorür 4-4. azobisiyanopentanailklorür) ve gümüş tuzları yardımıyla başlatılmış "katyonik polimerleşmesi değişik koşullarda incelenmiştir. Gravimetrik yöntemler yardımıyla tetrahidrofuranın katyonik palimerizasyonu için farklı sıcaklıklardaki hız sabitleri hesaplanmıştır. Ayrıca polimerizasyonun termodinamik parametreleri belirlenmiştir. Palimerler, U.V., I.R., 'H-NMR gibi spektroskopi k yöntemle rin yanı sıra G.P.C. ve viskozite yöntemleri kullanılarak da karakterize edilmiştir. Polimerizasyonun öne sürülen azo oksokarbenyum mekanizması doğrultusunda gerçekleştiği ve dönüşümün kullanılan karşı iyondan bağımsız olduğu saptanmıştır. Bu yöntem ile elde edilen azo bağı içeren politetrahidrofuran polimerlerinin blok kopolimer sentezinde kullanılabilirliğini belirlemek amacıyla yapılan ısısal bozunma deneyleri sonucunda herhir politetrahidrofuran zincirinin ısısal yada fotakimyasal aktif azo bağı içerdiği ortaya çıkmıştır. -v-

Abstract:
SYNTHESIS AND CHARACTERIZATION OF AZO-LINKED POLYTETRAHYDROFURAN SUMMARY In the applications-oriented polymer research the trend Is to concentrate more and mare an the improvement of established polymerization techniques and to develop composites from already available polymers. Such composites can be produced either by simply mixing two or more polymers together (Polymer Blends) or by joining the appropriate polymer via covalent bonds. The former is easier, most direct and cheaper way of producing new materials. However, the properties of such mixtures are very dependent on the mlscibility of the components. Immiscible polymer blends generally display disappointing mechanical performances due to lack of interfacial adhesion and to uncontrolled phase-separation processes. The latter leads, principally to either block or graft copolymers which because of the large number of possible structural variations, represent an enormous scientific challenge to understand the details of such systems. The other way of obtaining a polymer consisting of two different monomers is to copolymerize the monomers. Depending on the reactivities of two monomers, the copolymerization tends to yield either statistical or altenating copolymers. However, since the properties of products, such as Tg, gas permeabality and mechanical strength are determined by avarage composition, any improvement made by increasing the amount of monomer (M. ) leads to a consequent loss in the desirable properties of the comonomer (M2). The preparation of block copolymers was greatly stimulated by the development of living (i.e. terminationless) anionic polymerization technique. Preparing block copolymers using an anionic mechanism is certainly the best way of obtaining monodisperse copolymers, free of homapolymers, with well defined and predetermined structure and molecular weight. However, the living anionic polymerization technique although attractive, has some limitations. If the mechanism of propagation can be transformed from one best suited to the first monomer to that best suited ta the second monomer so on, then all monomers may be polymerized. for the preparation of block copolymers. Further consideration of this concept indicates that each transformation requires three distinct steps; the first introducing the functional group into polymer by living polymerization of first monomer using appropriate mechanism, the second involving termination of polymer, isolating the polymer and then dissolving it in an appropriate solvent -VI-containing the second monomer. The third step is an reaction on the functional group of the polymer to transform it into an active specie capable of polymerizing the second monomer. Palytetrahydrofuran has many desirable properties which have been utilized by industry in polyuretnane and polyester thermoplastic elastomers. In these applications; slow crystal iza- tion tendency of polytetrahydrofuran at room temperature is overcome by copolymerization, and difficulties in cross-linking are circumvented by introduction of copolymeric segments capable of forming networks. As a homopolymer, polytetrahydrofuran is currently too expensive to use with general-purpose or even specially elastomers, but as the soft segment of a thermoplastic elastomers, polytetrahydrofuran is widely used industrially. In these applications it is valued as a precursor leading to elastomers with outstanding hydrolytic stability, good low-temperature flexibility, outstanding thermal stability at elevated temperatures. The aim of this study is to investigate' a new method to prepare block copolymer of polytetrahydrofuran by cation to radical and reverse transformation polymerization. The cationic polymerization of tetrahydrofuran proceeds as a living system if the conditions are properly selected. In such a system each polymer chain has an oxonium ion as a chain end. If a bifunctional initiator is used, a bifunctional living pTHF is obtained. It has been shown that oxoca'rbenium ions with low nucleophilic counterions can easily be prepared by reacting an acid chloride with a stoichiometric amount of silver salt, such as silverhexofluarDantimonate (AgSbFg), silvertetrafluoroborate (AgBF),, and.silverhexafluorophosphate (AgPFg). R - CDC1 + AgSbF6 ~R - CH0+SbF6+ AgCl (I) The diacid chloride was prepared by reacting k.k*- aznbisCcyanopentanoic acid) with phosphorus pentachloride. ChL CH, I 3 j 3 H0DC-CH"-CH"- C - IV = N - C -. CH"-CH"-CDDH (II) I CN 0 DHL If I 3 I CN PC1.- 3 I 3 H CI - C -CH--CH-,- C-IM = I\I-C- CH"-CH"-C - CI (III)