Polimerik piridinyum tuzları sentezi ve katyonik fotobaşlatıcı olarak kullanımı
The synthesis of polimeric pyridinium salts and their use in photoinitiated cationic polymerization
- Tez No: 39760
- Danışmanlar: PROF.DR. YUSUF YAĞCI
- Tez Türü: Yüksek Lisans
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1994
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 59
Özet
ÖZET Düşük nükleofilik anyonlu piridinyum tuzlan fotokimyasal katyonik başlaücı olarak kullanılmaktadır. Bu çalışmada polimerik piridinyum tuzlan sentez edilmiştir. Bu amaçla, değişik bileşimlerde 2-vinil piridin - süren kopolimerleri serbest radikal polimerizasyon yöntemi ile sentez edilmiştir. Ele geçen kopolimerler m-kloroperbenzoik asit yardımıyla N-oksit haline dönüştürülmüş ve trietiloksonyum hekzaflorofosfat yardımıyla polimerik piridinyum tuzlannı vermek üzere alkillendirilmiştir. Bu polimerler asetonitril (CH3CN) gibi polar bir çözücüde çözünürken diklormetandaki (CH1CI2) çözünürlüğü polimer içindeki piridinyum miktan ile orantılıdır. Vinil piridin içeriği yüksek polimerlerde zincirler arası iyonik etkileşim sebebiyle çözünürlük azdır. Polimerin fotokimyasal davranışlan ve başlaücı özellikleri sikloheksenoksit, bütil vinil eter, N-vinil karbazol gibi monomerler üzerinde denenmiştir.
Özet (Çeviri)
THE SYNTHESIS OF POLYMERIC PYRIDINIUM SALTS AND THEIR USE IN PHOTOINITIATED CATIONIC POLYMERIZATION SUMMARY Photopolymerization plays an important role in various modern technical process. Typical applications pertain to uv curing of coatings on various substrates and hardening of inks and adhesives. The advantages of uv curing over other techniques include shorter curing cycles, reduced emission of volatile compounds, lower energy consumption and long time storage of fully formulated systems. Polymerizations may be initiated by polymeric or low molar mass initiators capable of becoming reactive after irradiation with electromagnetic radiation. The potential advantages of polymeric photoinitiators over conventional low molar mass analogous can be summarized as follows. First, low molar mass photoinitiators suffer from high volatility. Secondly, those photolysis products which are not consumed during the polymerization process may cause some undesired properties in the coatings such as acute smell. The use of polymeric photoinitiators, generally with photodissociable side groups, avoids these drawbacks. Additionally, graft copolymers or crosslinked networks may conveniently be prepared by selecting the number of photoactive groups along the polymer chain. The latter case has special importance in photocurable coatings. There is growing interest in industrial applications of cationic polymerization process for various techniques. Cationic polymerizations are initiated by substances (initiators) capable of either reacting spontaneously with polymerizable monomers upon mixing or becoming reactive after mixing upon heating or irradiation with electromagnetic radiation. Effective photoinitiators for cationic polymerizations are iodonium salts (RJ+X0, sulfonium salts (R3S+ X-) and selenium salts (R3Se+ X“), where X' is BF4\ PF6”, AsF6“ or SbFs\ Notably iodonium and sulphonium salts are thermally rather stable and, moreover, unreactive towards monomers capable of undergoing cationic polymerization. The reaction mechanism, which is generally accepted, at present, is described in the following: ArJ”X“ ----> Arr X”+ Ar. (i) Ar3S+ X- -&-> Ar2S; X“ + Ar. (ii) VISubsequent hydrogen abstraction from solvent or monomer yields Bronsted acid which can initiate the polymerization of appropriate monomers. Arl+ + RH > Arl + H+ + R. Ar2S; + RH > Ar2S + H+ + R- (iii) (iv) The pyridinium salts, a new class of photoinitiators are also effective photoinitiators for cationic polymerizations of cyclic ethers such as cyclohexene oxide and vinyl ethers such as n-butyl vinyl ether. N-alkoxy pyridinium and N-alkoxy-quinolinium salts of the general structure CI fsT+PF I OEt r + PR. OEi II CO III can act indirectly as photoinitiators of the cationic polymerization of appropriate compounds. In this case they do not absorb light but oxidize photolytically formed free carbon centered radicals. This reaction results in the formation of reactive carbocations. Moreover, pyridinium and isoquinolinium salts were found also to act directly as photoinitiators provided the irradiation is performed at wavelengths corresponding to their absorption bands. If the pyridinium ring is appropriately substituted, the absorption band is shifted to longer wavelengths. A mechanism put forward to explain the ability of pyridinium salts such as N-Ethoxy-2- Methylpyridinium Hexafluorophosphate (I) to induce the polymerization appropriate monomers is shown below. OEt N' CH.\ - I * + R-H + OEt- (v) + R- (vi) Vll+ H+ (vii) NT CH, *- Polimer (viii) H f - M-*- Polimer (ix) Notably, radical cations formed upon irradiation, and/or protons, can be responsible for polymerization. This mechanism was substantiated by recent flash photolysis studies. Polymeric pyridinium salts were synthesised in analogy to the method described by Reichardt. For this purpose, copolymers of poly 2-vinylpyridine with polystyrene in different ratios have been synthesised. The copolymers (PSV) were prepared using the related monomers in free radical polymerization process in bulk. 2,2 Azobisisobutyronitrile (AIBN) was used as an initiator. The results of the copolymer ratios of 2-vinylpyridine with styrene are presented in Table 1. Table 1. Copolymer Ratios of 2-Vinylpyridine with Styrene VlllM«MWW CH2=CH CH2=CH >N -' » N J U ^ (x) Each copolymer sample was then oxidized by using m-chloroperbenzoic acid to give N-oxide derivative of the corresponding polymer. Subsequently N-oxide polymers were treated with triethyloxonium hexafluorophosphate. ^CH2-CH-CH2-CH^WS' ^/^C^-CH-CH^-CH-^ ^ m-chloro ^ perbenzoic acid -w^CH2-CH-CH2-CH'^^^. (xi) ***** o ÖT PF6 Polymeric pyridinium salts are soluble in acetonitrile but the solubilities of polymers in dichloromethane are proportional to pyridinium ion content. Insoluble fractions were much higher for those with high vinyl pyridine content. This behavior may be explained by the possibility of ionic interaction between chains. (xii) Optical absorption spectra of monomelic and polymeric pyridinium salts (a) and (b) are shown in Figure 1. The absorption maxima are located at 265 nm which indicates spectral similarity in both cases. IXE o ”o E ö Ol 250 300 X (nm) 350 Figure 1. Optical absorption spectra of the compounds (a) and (b) recorded in acetonitrile solution at room temperature. (a) Poly-(N-Ethoxy-2-Vinyrpyridinium Hexafluorophosphate) (b) N-Ethoxy 2-Metylpyridinium Hexafluorophosphate) Polymeric pyridinium salts are capable of acting as photoinitiators for the polymerization of appropriate compounds such as epoxides and alkyl vinyl ethers that can not be polymerized by a free radical mechanism. In this work, we have used cyclohexeneoxide (CHO), butyl vinyl ether (BYE) and N-vinyl carbazole (NVC) as cationically polymerizable monomers. Typical results concerning the polymerization of these monomers initiated by polymeric pyridinium salts are also presented in Table 2. Polymerizations are carried out in bulk, in acetonitrile and in dichloromethane according to their solubilities. The rate of polymerization depends on the initiator concentration and photolysis time. The conversion to polymer increases with increasing the pyridinium ion content in the polymeric initiator. The possibility of using these polymers as positive photoresist material was also checked. As a crude demonstration, a film of polymeric pyridinium salt was irradiated at around 300 nm. The insoluble polymer became soluble in dichloromethane after photolysis.O cs OS CO «J E“3Î S © c o o s N - ”S es XI
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