N-izopropilakrilamid-itakonik Asit Kopolimerlerinin Sentezi Ve Karakterizasyonu

Abstract

Bu çalışmada 1 adet poli Itakonik Asit (PIA), 1 adet poli-N-izopropilakril amid (PNIPAAM), 5 adet NIPAAM-IA kopolimeri ve 1 adet NIPAAM-AA kopolimeri olmak üzere toplam 2 adet homopolimer ve 6 adet kopolimer sentezlenmiştir. Poümerler 50°C'de, K2S208 başlatıcısı kullanılarak, azot atmosferinde ve yüksek dönüşüm sağlayacak farklı sürelerde hazırlanmıştır. Elde edilen homo ve kopolimer örneklerinin FTIR kullanılarak spektrofotometrik karakterizasyonu yapılmıştır. Homo ve kopolimerlerin geçiş sıcaklıklarını izlemek amacıyla 400 nm'de, geniş bir sıcaklık ve PH aralağında UV-spektrumları çekilmiş ve kopolimerlerdeki IA yüzdeleri arttıkça geçişin daha yüksek PH ve sıcaklıklara kaydığı gözlenmiştir. Örneklerin NaCl, su ve tampon çözelti içerisinde kondüktometrik titrasyonlan yapılmış ve iletkenlik ölçüm sonuçlarından zayıf asit yapısındaki PIA' in ve kopolimerlerin ayrışma sabitleri hesaplanmıştır. Polielektrolit özelliğinde olan örneklerin fosfat tamponunda yapılan viskozimetrik ölçümlerinden [r\] ve k1 (Huggins sabiti) hesaplanmıştır.

The behaviour of a polymer in a given medium reflects the balance of like and unlike interactions among its own segments and the surrounding molecules. In the case of aqueous solutions, the solvent-solvent interaction in water is particularly strong as indicated by its partially ordered structure. Indeed, the eccentric physical properties of water control the conformations and the subsequent reactions of biological macromolecules that are responsible for life on Earth. From the studies of PNTPAAM solutions it appears that below the lower ciritical solutions temperature (LCST), PNIPAAM exists as isolated, flexible but extended coils in dilute aqueous solutions. At the LCST, it appears that the individual polymer chains collapse prior to aggregation. The visual observation of macroscopic phase seperation upon heating is among the employed techniques. This rather simple method of determining the LCST is commonly known as the cloud point method. Various researchers have somewhat quantified the method by using a standard UV- VI S spectrophometer. For the having hypdrophobic with both hydrophilic portions posses LCSTs is a rather general phenomenon. Various researchers followed concept that "as a polymer which is soluble at all temperatures is made increasingly hydrophobic, before complete water insolubility is reached, a range of compositions will be found which will have temperature inverse solubility and more hydrophobic the increment, the lower the LCST". The ability to shift the LCST of PNTPAAM- like polymers from < O to > 100°C provides excellent flexibility in tailoring transitons for specific uses. One can "switch off' solubility at biologically relevant temperatures as well as at room temperature. The morover, the fact that one can obtain the same LCST with a small amount of a very hydrophobic comonomer or a high fraction of a less hydrophobic comonomer permits further modulation of interactions with cosolutes in the system. In this work, we aimed to investigate the effect of pH, composition of the copolymer and temperature on the conformations (coil-globule transitions) of the PNIPAAM, PIA (polyelectrolyte) and copolymers. For this reason, PNIPAAM, PIA and five NTPAAM-IA copolymers containing both hydrophilic and hydrophobic unit were syntesized. The polymers were prepared by a free radical polymerization using K2S2O8 initiator in water at 50°C. The polymerazitaion conditions are given in Table 1. Table 1. The synthesis conditions of homo and copolymers (*) % 10.0 AA Total reaction volume = 25 ml T= 50° C The phase transitions of these samples were traced by monitoring the transmittance of a 400 nm light beam at different temperatures and pH on a UV-visible spectrophotometer. The phase diagrams o fthe aqueous solutions of PNIPAAM and Polymer No: 6 are shown in Figure 1 and Figure 2. A striking feature shown in Figure 1 and Figure 2 is that the phase transition of this aqueous solution of PNIPAAM takes place as temperature reaches 35°C and independently of pH of the medium while in the case of Polymer No: 6 cloud point changes with pH of the solution. It means that a characteristic dimensional change of the chain molecules (coil-globule transition) occurs in aqueous solution and electrostatic interaction between hydrophilic groups on the chain effect the transition temperature in the case of Polymer No: 6. The conductometric titrations of synthesis polymers were carried out. The aqueous solutions of the polymers were titrated with 0. IN NaOH. The conductivities were plotted versus the mililiters of titrants. The equivalence points correspond to the carboxyl content of the polymers. The conductometric titration curves for PIA and Polymer No: 6 is shown in Figure 3 and Figure 4. XI 2 50 H 240 2.20 1.80 _ SO E o o İ 40 a a 20 00 0.80 0 60 -| 0.40 0 20H Î00 Polımer No 7 «XI I XI.. I. l TpH=2.00 AphU4.12. pH=5 69 apH = 705 OpH=915 20 24 28 32 35 40 44 4 8 52 5'6 60 T, -C Figure 1. Temperature and pH dependence of phase transition of aqueous PNIPAAM 20 24 2» 32 36 40. 44 -» I.'C 48 52 56 64 M 72 Figure 2. Temperature and pH dependence of phase transition of Polymer Î" Xll 340ı .120 300- 2.80 2 00 2.40 2.20- 200- 180- I GO 1.40 I 20- 100- 080- 0 60. 0 40 020........' 0 00 Polimer No:l 8 10 12 14 16 18 20 V, ml (0.1 N NoOH) Figure 3. The conductometric titration curves of PIA (in water) 2.20 1.80 O ~ 1.A0 r E E. ı.oo 0.60 0.20 Polimer No. 6 2 U 6 -* V,mI(0.1N NqOH) Figure 4. The conductometric titration curves of Polymer No: 6 xiu In order to calculate the ionisation constant of the hydrophilic monomer (IA) in the structure of the samples which is used in this work the conductivity values of polymers were measured at different concentrations. 1 / A values were plotted versus Ac by using Ostwald Dilution Law and calculated K, ionization constants values of these constants for all homo and copolymers are given in Table 2. Table 2. Intrinsic viscosities and ionization constants of homo and copolymers. * % 10.0 AA ** Tisp / c -c doğrularından elde edilen kayım Extrapolation values obtained from.% / c - c graphics Polyelectrolytes are ionizable compounds which consist of at least one macromolecular ionic species. Polyitaconic acid belongs to the group of weak polyacids. The solution properties of polyelectrolytes are influenced by their polymer character. The reduced viscosity of the polyelectrolyte solutions increase with dilution. Addition of salt eliminate the rise in rjsp/c at low concentration. So, intrinsic viscosities of the polymers which is prepared in this work were determined in phosphate buffer containing 0.1 N NaCl [rj] values ve k', Huggins constants of the polymers are given in Table 2.