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Yaşayan polimerizasyon sistemlerini içeren dönüşüm reaksiyonları ile blok ve graft kopolimer sentezi

The Synthesis of block and graft copolymers by using transformation reactions involuing living polymerization systems

  1. Tez No: 100774
  2. Yazar: AYŞEGÜL BAŞKAN DÜZ
  3. Danışmanlar: PROF.DR. YUSUF YAĞCI
  4. Tez Türü: Doktora
  5. Konular: Kimya, Chemistry
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2000
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 148

Özet

YAŞAYAN POLİMERİZASYON SİSTEMLERİNİ İÇEREN DÖNÜŞÜM REAKSİYONLARI İLE BLOK VE GRAFT KOPOLİMER SENTEZİ ÖZET Yeni özelliklere sahip polimerlerin dizaynı ve sentezi polimer kimyasında gittikçe artan bir öneme sahiptir. Yaşayan polimerizasyon, kontrol edilebilen moleküler ağırlık ve düşük moleküler ağırlık dağılımı ile polimer sentezi için önemli bir tekniktir. Fakat bütün istenen özelliklerin bir homopolimer üzerinde sağlanması olanaksızdır. Bu amaçla istenen özellikleri içeren uygun homopolimer ile makrofaz ayrımı olmaksızın blok ve graft kopolimerler sentezlenebüir. Yaşayan iyonik polimerizasyon teknikleri, safsızlıklara karşı hassas olması yanında iyonik olarak polimerleşebilen monomerler ile sınırlıdır. Blok kopolimer sentezinde kullanılan monomer sayışım artırmak için, polimerizasyon mekanizmasının birinden diğerine değiştirildiği dönüşüm reaksiyonları oldukça önem kazanmıştır. En yaygın ve en çok üzerinde çalışmalar yapılan metod çeşitli polimerizasyon mekanizmalannm kullanıldığı dolaylı dönüşüm reaksiyonlarıdır. Kararlı fakat ikinci polimerizasyon mekanizması için potansiyel olarak aktif fonksiyon taşıyan grup, ilk monomerin polimerizasyonu sırasında başlama yada sonlarıma aşamasında zincire ilave edilir. Polimer izole edilir ve saflaştınlır, sonuç olarak fonksiyonel gruplar aydınlatma, ısıtma veya kimyasal reaksiyon gibi dışardan bir etki ile başka türlere dönüştürülür. Çalışmamızda dönüşüm reaksiyonlarım kullanarak çeşitli yaşayan polimerizasyon mekanizmalarım içeren blok ve graft kopolimerler sentezlemeyi amaçladık. İlk olarak, yaşayan katyonik polimerizasyon ve kararlı radikal polimerizasyon (Stable Free Radical Polymerization-SFRP) yöntemlerinin birleştirilmesi ile stiren ve tetrahidrofuran blok kopolimerleri hazırlanmıştır. Yaşayan katyonik polimerizasyon yöntemi ile elde edilen kararlı radikal sonlu polimerik başlatıcı, stirenin SFRP'da kullanılmıştır. Böylece her iki blok kısmı kontrollü polimerizasyon yöntemi ile sentezlenmiştir. Kararlı radikal sonlu PTHF, TEMPO varlığında azo bağının ısısal bozunması ile elde edilmiştir. TEMPO-PTHF ve stirenin 125 °C'deki polimerizasyonu, blok kopolimer oluşumu ile sonuçlanmıştır. Bu proses (SFRP) kendiliğinden başlama ve kararlı serbest radikal (Stable Free Radikal-SFR) ile polimer radikalin geri dönüşümlü sonlanması şeklinde gerçekleşir. CH2-CH-0-N~)“ * ww*w.CH2-CH + -O-nT} (1) ıxYukarıda açıklanan sisteme benzer olarak, TEMPO grubu içeren prepolimerler fotokimyasal olarak da elde edilmiştir. Benzoin ve türevleri UV kaplama teknolojisinde kullanılan oldukça iyi bilinen başlatıcılardır. Özellikle benzoin grubu taşıyan polimerler graft ve blok kopolimer sentezi için büyük öneme sahiptir. Bu amaçla benzoin sonlu veya yan zincirde benzoin grubuna sahip poli(metil metakrilat)'lar sentezlenmiş ve aşırı TEMPO varlığında 350 nm'de aydınlatılmıştır. Kararlı nitroksil radikali hem polimerik hidroksibenzil hemde düşük molekül ağırlıklı benzoil radikalinin her ikisiyle de reaksiyona girer. Böylece kararlı radikal ile benzoil radikalinin birleşmesi ile oluşan ve homopolimer oluşumuna neden olan ürün, THF'de çözülüp tekrar metanole çöktürme işlemi sırasında ortamdan uzaklaştırılır. Daha sonra TEMPO içeren prepolimerler stirenin radikal polimerizasyonunda makrobaşlatıcı olarak kullanıldı. Oysa blok ve graft kopolimerizasyon sırasında uç grupta ve yan zincirde fonksiyon taşıyan her iki polimerin molekül ağırlığında azalma olduğu görülmüştür, yani PMMA bozunmaya uğramıştır. Sonuç olarak metakrilatlann kararlı radikal ortamlı yaşayan radikal polimerizasyonu hem proton transfer reaksiyonu ile sonlanma hemde yüksek sıcaklıkta polimer zincirinin bozunması yüzünden başarılamamıştır. Molekül ağırlığındaki azalmanın polimerin yapışma bağlı olup olmadığını kontrol etmek için, benzer yolla TEMPO sonlu polistiren (M”:56500, Mw/Mn:2.4) hazırlanmıştır. Prepolimerin stirenin radikal polimerizasyonunda kullanılması ile zincir büyümesinin gerçekleşmesi (Mn:76000, MJMn:2.5) fotokimyasal olarak hazırlanan ve TEMPO içeren PSt prepolimerin radikal polimerizasyon sırasında bozunmaya uğramadığını göstermiştir. Bir diğer transformasyon reaksiyonu atom transfer radikal polimerizasyon ve radikal etkili katyonik polimerizasyon mekanizmalarının birleştirilmesi ile gerçekleştirildi. /7-Metoksi stiren ve stiren ile siklohekzen oksit blok kopolimerleri, ATRP'dan ve radikal etkili katyonik polimerizasyon yöntemleri ile hazırlanmıştır. ATRP Cu(I)/Ligand sistemi ile katalizlenen yaşayan radikal polimerizasyon yöntemlerinden biridir. Bu polimerizasyon yöntemi, organik halojen ile Cu(I) tuzları gibi geçiş metalleri arasındaki redoks reaksiyonu yoluyla karbon-halojen bağının geri dönüşümlü homolitik bölünmesini içerir. MOS ve St'in bulk polimerizasyonu, 1- Bromoetilbenzen başlatıcı varlığında, CuBr katalizör ve kompleks yapıcı ligand olarak dNbipy kullanılarak gerçeldeştirilmiştir. Pn-X + Cu(l)/2bip7f

Özet (Çeviri)

THE SYNTHESIS OF BLOCK AND GRAFT COPOLYMERS BY USING TRANSFORMATION REACTIONS INVOLVING LIVING POLYMERIZATION SYSTEMS SUMMARY Design and synthesis of materials with novel properties is becoming an increasingly important aspect of polymer chemistry. Living polymerization is an essential technique for synthesizing polymers with well defined structure (i.e., polymers with controlled molecular weight and narrow molecular weight distributions). Quite often desired properties are not attainable by the properties of a single homopolymer. Most notably, block and graft copolymers consisting of several types of monomer sequences are of special interest because they combine the properties of the corresponding homopolymers without macrophase separation. Living ionic polymerization is elegant method for the controlled synthesis of block copolymers. In order to extend the range of monomers for synthesis of block copolymers, transformation approach was postulated by which the polymerization mechanism could be changed from one to another which is suitable for the respective monomers. The most popular and best documented method is indirect transformation which uses various polymerization modes. The stable but potentially reactive function group for the second polymerization mode is introduced to the chain ends either in the initiation or the termination steps of the polymerization of the first monomer. The polymer is isolated and purified, and finally the functional groups are converted to another kind of species by external stimulation such as photoirradiation, heating or chemical reaction. Our work describes the synthesis of block and graft copolymers consisting of living polymerization systems by transformation reactions. Firstly, we have combined living cationic polymerization and stable free radical polymerization (SFRP) methods for the preparation of block copolymers of tetrahydrofuran and styrene. Transformation of the initiating sites was achieved by the thermal decomposition of an azo-linked polytetrahydrofuran, obtained by means of cationic polymerization, in the presence of TEMPO. By the polymerization of bulk styrene with TEMPO terminated PTHFs at 125 °C, the corresponding block copolymers were obtained. SFRP is based on the simultaneous initiation and the reversible termination of the polymer radical with the SFR. -OW»o£> ^~ -CHH* ?.»£> (1) XlllSimilarly, TEMPO incorporated prepolymers were also obtained by photochemically. Benzoin and its derivatives are well known photoinitiators which find commercial application in UV curable coatings. Especially, polymers with benzoin groups are of great importance for the synthesis of block and graft copolymers. For this purpose, poly(methyl methacrylate)s possessing side chain or terminal TEMPO units were prepared by irradiating corresponding benzoin- containing polymers at A,=350 nm in the presence of the excess TEMPO. The stable radical reacts with both polymeric hydroxybenzyl and low molar mass benzoyl radicals. The combination product of TEMPO with a benzoyl radical was removed by reprecipitation from THF solution into methanol. In a subsequent reaction the polymers with TEMPO units were subjected to heating at 125 °C in the presence of styrene. However it turned out that poly(methyl methacrylate)s underwent degredation, which was concluded from the fact that the molecular weight of the polymers reduced with both side chain and terminally functionalized polymers. As a result, stable radical mediated living radical polymerization of methacrylates is not successful, not only because of an irreversible termination but also because of chain scission of the polymeric chains formed at elevated temperatures. In order to check if the reduction in the molecular weight was due to the nature of polymer, TEMPO- terminated polymers of styrene were prepared in a similar way (Mn:56500, Mw/Mn:2.4). Interestingly, under similar experimental conditions, chain extension way (Mn: 76000, Mw/M“:2.5) and grafting reaction upon thermolysis in the presence ofStoccured. We have demonstrated another novel method for radical/cation transformation which combines the atom transfer radical polymerization (ATRP) with promoted cationic polymerization and utilized it for the preparation of block copolymers of St monomers with cyclohexene oxide. ATRP involves the reversible homolytic cleavage of a carbon-halogen bond by a redox reaction between an organic halide (R- X) and transition metal. Bulk polymerization of MOS and St was performed using 1- bromoethyl benzene, as an initiator, CuBr as a catalyst and dNbipy (4-4'-di-(5- nonyl)-2,2'-bipyridine) as a complexing ligand. Prr-X + Cu(l)/2bipy~P «T** Pn + X-Cu(ll) / 2bip71 A. \ V *.) Monomer In the case of jt?-methoxystyrene (MOS) monomer only low molecular weight products were formed (Mn:1300, Mw/Mnrl.19). Further attempts, by changing various reaction conditions, to obtain polymers with higher molecular weight failed. On the other hand, high molecular weight polymers were obtained with styrene monomer. This monomer does not possess a strong electron donating substituent and ATRP works better. Polymers obtained by ATRP acted as alkyl halide to generate radicals in the presence of Cu(I) and dNbipy in the second step. Electron transfer reaction from polymethoxy stryl (or polystryl) radicals to onium ions gives polymeric cations capable of initiating polymerization of CHO. The 'H-NMR spectrum of the block copolymer (Table 5.8, run 1) displays signals corresponding to -OCH3 protons at 3.8 ppm and to -OCH2 protons at 3.4 ppm, indicating the existence of both MOS and CHO segments. The mole composition of the block copolymer (%23 MOS and %77 CHO) XIVdetermined by the ratio of aromatic protons of the PMOS to O-CH protons of the PCHO segment. This ratio determined by SEC, % 18 MOS % 82 CHO. Scheme 5.10 shows the signals of the atomatic protons of PSt 6.4-7.2 ppm in addition to the signals corresponding to PCHO segments. Moreover, the synthesis of well defined block copolymers of CL and St has been prepared by transformation of living ring opening polymerization into inker process. Poly(s-caprolactone) has a great importance with respect to their uses as biodegredable and biocompatible materials in medical applications. It is well known that aluminum isopropoxide is a very effective initiator of e-CL polymerization. The ring opening polymerization proceeds through a coordinative insertion of the CL into the Al-0 bond of the initiator and involves the selective cleavage of the oxygen- carbonyl bond of s-CL. AKOip^ n e”CL > iPrOffe^CH^q^Al/ -^ %99 (3) O iPrOfA-(CH2)5ÖkH The polymerization in the propagating step is actually a living process that leads to a polymer with a narrow molecular weight distribution. The concept of iniferter (initiator-transfer agent-terminator) was proposed by Otsu et al. for the design of the polymer chain end structure. In the first step, ring opening polymerization of CL was carried out by using triphenyl methanol as the initiator and aluminum alkoxide as the promoter, respectively, to give triphenylmethyl (trityl) terminated polymer. Trityl terminated poly(s-CL) was characterized by 'H-NMR, UV spectral analysis and SEC measurements. The 'H-NMR spectrum of PCL exhibits weak signals at 7.4 ppm corresponding to prtons in addition to peaks at 4.05 and 2.3 ppm for ( CH2-O) and (COOCH2), respectively. The molecular weight (M“: 3300) which was determined from the integration ratios of the signals was in good agreement with that obtained by the SEC method (Mn: 6000, the PSt equivalent molecular weight). Trityl terrninated PCL was used as a thermal initer in the polymerization of St. Upon heating, the active chain end group undergoes reversible dissociation. The oxygen centered radical reacts with the monomer whereas the trityl radical reacts only with the propagating radical. The resulting polymer was confirmed as a block copolymer after examination of IR and NMR spectra and SEC trace of the polymer. FT-IR spectrum of the CL and St block copolymer exhibits bands characteristic of the carbonyl group of PCL at 1730 cm”1 and the aromatic group of PSt at 3080 cm“1, 1600, 1452 cm”1. The ^-NMR spectrum of the block copolymer displays signals corresponding to the aromatic protons in the range of 6.4-7.5 ppm in addition to the characteristic PCL signals. XVFinally, the synthesis of a high glass transition temperature (Tg) N-substituted maleimide-methylvinylisocyanate copolymer with TEMPO moiety at the side chain, and the application of this polymer as a polymeric counter radical in the radical polymerization of styrene to yield corresponding graft copolymers. The polymers of JV“-phenylmaleimide and its derivatives have been known to exhibit high Tg due to the rigid imide rings in the backbones. The polymerization of vinyl isocyanate with maleic anhydride is known to be alternating and similar tendency for the maleimide systems is also observed. There is one reactive isocyanates group in every repeating unit of the copolymer. In a subsequent process, the polymers can be functionalized by reaction with hydroxy group of 4-hydroxy TEMPO. For this purpose, to solution of the maleimide-methylvinylisocyanate copolymer, in dry THF was added 4- hydroxy-TEMPO (2.34 mmol) and 2 mol % of dibutyl-tin-dilaurate as a catalyst. The mixture was stirred at 50 °C for 5 days under nitrogen atmosphere. Decomposition of NCO group was followed by the change in intensity of the peak at 2254 cm”1 in the IR spectra of the polymer during the reaction. The IR and 'H-NMR spectra prove the expected structure of the polymer. The 'H-NMR measurement of the TEMPO incorporated product was performed in the presence of phenylhydrazine since TEMPO moiety can easily be reduced by hydrazines to the corresponding hydroxy lamine. According to the 'H-NMR spectrum, the signals originating from TEMPO were discerned at 1.26, 1.42, 1.62 and 1.86 ppm. These signals were assigned to two types of methyl protons, axial and equatorial and two methylene ones axial and equatorial, respectively. The signal at 5.17 ppm also originates from TEMPO and assigned to the OH protons. Radical polymerization of styrene was performed with BPO as an initiator in the presence of the above obtained prepolymer. Usual stable radical mediated polymerization prodecure was followed Le., 125 °C after being held at 95 °C for 3.5 h. Although the presence of polystyrene graft was evidenced by 'H-NMR spectra, estimation of the composition of the graft copolymers was not possible since the peaks of the aromatic protons of styrene overlap with those of the phenyl isocyanate groups. As can be seen from DSC measurements, two distict glass transition temperatures representing those of the backbone and graft chains are observed indicating incompatibilty of the both segments. In conclusion, the synthesis of phenylmaleimide-methyl vinylisocyanate copolymers with nitroxyl radicals at the side chains was achieved. The resulting polymers were able to serve as polymeric counter radicals in the polymerization of styrene to give the corresponding graft copolymer. XVI

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