Poli(dimetilsiloksan) içeren poli(vinil pirolidinon)blok kopolimerlerinin sentezi ve karakterizasyonu
Preparation of poly (Dimetyhl siloxane) containing poly (Vinyl pyrrolidinone) block copolymers and characterization of the products
- Tez No: 68902
- Danışmanlar: DOÇ. DR. NURSELİ UYANIK
- Tez Türü: Yüksek Lisans
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Kimya Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 64
Özet
ÖZET Bu çalışmada değişik uzunluklarda poli(dimetil siloksan) segmanlan içeren A-B-A tipi blok kopolimerler aşamalı yöntemle sentez edilerek yumuşak ve sert blokların bir arada tutulabildiği termoplastik elastomerler elde edilmiştir. Bu amaçla önce, hidroksil uç gruba siloksanlı prepolimerler, 60°C'de bir alifatik diizosiyanat ile kaplama reaksiyonuna sokulmuş ve 1. aşama sonunda diizosiyanat sonlu üretanlar elde edilmiştir. Bu aşamada zincir uzaması istenip, istenmediğine göre reaksiyon koşullan ayarlanmıştır. 2. aşamada ise (-NCO) son grupları bulunan bu üretanlann oda sıcaklığında, kuru azot atmosferinde, katalizör eşliğinde ve karanlıkta bir hidroperoksit ile reaksiyonu gerçekleştirilmiştir. Makro başlatıcılann (prepolimer diperkarbamatlann) molekül ağırlıkları analitik yöntemle veya jel geçirgenlik kromatografisi ile belirlenmiştir. Bu reaksiyonlar sonunda elde edilen ve zincir uçlarında peroksit bulunan makro başlatıcılar, vinil pirolidinonun polimerizasyonunda kullanılarak diklorometanda çözelti polimerizasyonu yöntemi ile A-B-A tipi blok kopolimerler sentez edilmiştir. Analitik ve spektroskopik (İR) olarak ara ve son ürünlerin yapılan tanınarak kopolimerlerin molekül ağırlıklan viskozimetrik ve ICP yöntemleri ile tayin edilmiştir, örneklerin termal davranışlan DSC ölçümleri ile belirlenmiş ve silikonun kopolimer yapısında plastifiyan gibi davranarak Tg'i (camlaşma geçiş sıcaklığını) ve Tm'i (erime noktasını) düşürdüğü termogramlardan izlenmiştir. Tensilonda yapılan çekme deneyi ile elde edilen yük-uzama eğrilerinden örneklerin kopma-uzaması, çekme ve kopma mukavemetleri ile Young modülleri hesaplanmıştır. Silikon miktarı arttıkça kopma uzamasının arttığı, kopma ve çekme mukavemetleri ile Young modülünün azaldığı belirlenmiştir.
Özet (Çeviri)
SUMMARY The preparation of linear block copolymers via functionally terminated oligomers was reported firstly about 30 years ago. In these types of synthesis, the prepolymers have functional groups, such as diols, diisocyanates, hydroperoxides, and azo-compounds. These prepolymers are used to synthesize a macro initiator for using in vinyl polymerization. On the other hand, the preparation of the chemically linked siloxane to A-B, A-B-A or segmented (A-B)“ type copolymers have been used for about 20 years. The resulting copolymers range from thermoplastics to thermoplastic elastomers depending the nature of the blocks, block lengths and the copolymer composition. These synthesis usually show two phase morphologies where there are hard segment domains for the continous siloxane phase. As it is known that, polysiloxane, especially poly (dimethyl siloxane) have extremely interesting properties. These properties include extremely low glass transition temperatures, very high chain flexibility, good oxidative, thermal and UV stability, hydrophobicity, biocompatibility, high gas permeability and surface activity (low surface energy). Despite many unique properties, thermodynamic incompatibility of poly (dimethyl siloxane)s with almost all other organic polymer systems is due to very low solubility parameters. In this work copolymers of poly (vinyl pyrrolidinone) (PVP) and poly (dimethyl siloxane) (PDMS) were prepared by using stepwise procedure. The preparation procedure of the copolymers by these methods are given below. The macro initiators are prepared firstly and their use in the copolymer synthesis is the last step. The preparation of macro initiator is composed of two stages. At first stage, the dried hydroxyl-terminated PDMS and the aliphatic diisocyanate (IPDI), were reacted at 60°C in bulk under a blanket of dry nitrogen. The molar ratios of diisosyanate to prepolymer were taken to be three or one. -VI-If we chose the ratio as three, the chain extension is prevented. If the chain extension is desired the molar ratio must be taken as one. After the determined chain extension period, more IPDI added to the reaction mixture to be sure to obtain the (-NCO)capped prepolymer. The resulting product were decantated with dried acetonitrile in order to separate the excess of diisocyanate. The product was dried at room temperature in vacuo. The isocyanate contents of the urethane type products were determined by end group titration of isocyanates and the results were also given in Table 1. In the second step of preparation of macro initiator, the isocyanate-terminated urethans were reacted with dried t-butyl hydroperoxide (t-BHP) methylene chloride solutions. A few drops of T -12 catalyst were added to the reaction mixture. The reaction was carried out under a dry nitrogen blanket, at room temperature, in dark for 200 h. The molar ratio of t-BHP to urethane was approximately three to prevent undesired chain extension. The resulting product was isolated by decantating in acetonitrile and dried in vacuo at room temperature. The molecular weight of the macro initiators in which the molecular weight of the prepolymer kept constant were calculated from their peroxide contents. The molecular weights of the macro initiators prepared from the chain extented urethanes were determined by GPC method. The preparation conditions of macro initiators are given in Table 1. The prepared macro initiators (M.I.) were used in the synthesis of copolymer of VP. Weighed amounts of Mi's were mixed in predetermined amounts of monomer (VP) and solvent. The solvents used are methylene chloride or ethanol. The mixtures were distributed in Pyrex tubes and then degased on the vacuum line. The solutions were immersed in thermostatically controlled baths and polymerization were carried out at 60°C for desired polymerization period. The solid products were dissolved in ethanol and then precipitated in large volumes of toluene. The copolymers were filtered and dried in vacuo at room temperature. Results and Discussions Nine copolymers of VP were synthesized from three different macro initiator. The weight percentage of PDMS incorporated into the polymeric product ranged from 7 to 30 %. The intermediates and the products obtained were characterized by IR spectroscopy. In the IR spectra, the (-OH) absorption peaks were disappeared at the end of capping reaction with diisocyanate. The peak at 2280cm”1 is due to stretching vibration of (-NCO). The peaks around 3440cm“1 and 1730cm”1 are due to the (-NH) streching and carboxyl stretching vibrations respectively of the (-NH-O0) group in the urethane formed. At the end of 2nd step the disappearance of the (-NCO) peaks indicate the formation of macro initiator. The main absorption peaks of M.I. and homo-PVP are also shown together in the IR spectra of copolymers. -vn-The characteristics of copolymers are given in Table 2. The intrinsic viscosities were determined in chloroform solution at 25°C. As the proportion of PDMS incorporated into the polymeric material increases, the overall conversion of VP to polymer and the intrinsic viscosities of the final copolymeric products decrease. The ICP studies of block copolymers have resulted 28.3 ppm. (c= 0.4826 g/100 ml.) and 27.1 ppm.(c=0.4816 g / 100 ml.) in the sample No. 1-3 and No.II-3a respectively. These results yield 0.586 and 0.563 percent silicon in the samples. The molecular weight of the copolymers can be estimated as 14.9 x 104 g / mol and 165.5 x 104 g/mol for the samples No.I-3 and No.II-3a respectively. The thermal characterization of the copolymers were obtained by Differential Scanning Calorimetric (DSC) thermograms. In the DSC thermograms the glass transition temperature (Tg) and the melting temperature (Tm) values of PVP segments were lowered in the copolymers due the plasticizer effect of PDMS with the comparison of homo-PVP values. These lowering depends on the PDMS weight percent incorporated into the copolymers. The mechanical characterizations of the copolymeric films were done by using stress strain curves obtained from Tensilon. The films were prepared by solvent casting method by use of a 50/50 (v/v) mixture of ethanol-dichloro methane. Ultimate tensile strength (UTS), percent elongation (UTE) and Young's modulus (YM) were calculated and the average value of the mechanical properties were given in Table 3. The yield is obtained only in three samples and then the tensile strength of these samples can be calculated. Tensile strength (TS), UTS, ultimate elongation (UTE) and YM of the copolymers decrease with increasing of PDMS content in samples. -vui-IXu s o a o U u o 3 a %-* C3.a u a ?*-» u CS I- « u 73 S s. >“o a o U u o PQ B O.p* ??J es.a u *i u es u es JS U ”3 u 'S es JS o es H XI
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