POLİ(N-İZOPROPİLAKRİLAMİT) İN POLİ(ETİLEN TERAFTALAT) YÜZEYİNE DOKU MÜHENDİSLİĞİ UYGULAMALARI İÇİN FOTO BAŞLATMA YOLUYLA AŞILANMASI

Abstract

The preparation of stimuli-responsive surfaces has attracted increasing attention due to their potential applications in biological science and engineering. These stimuli-responsive surfaces are usually prepared by modification of substrates with environmentally responsive polymers that can respond to environmental stimuli such as temperature, light, pH, electric field, ion strength, and magnetic field. Among various responsive polymers used to prepare stimuli-response surfaces, thermally responsive poly(N-isopropylacrylamide) (PNiPAAm) is the most popular one because it exhibits a reversible phase transition at around 32 ºC (known as the lower critical solution temperature, LCST). At a temperature below its LCST, the polymer chains are swollen and soluble in water, whereas at a temperature above the LCST the chains collapse and become insoluble in water. As such it has received great attention for the preparation of thermo-responsive surfaces for tissue engineering. Poly (ethylene terephthalate) (PET) is one of the most widely used polymer materials in biological, chemical, and medical sciences because of its perfect properties such as convenient processability, mechanical strength, thermal stability and optical transparency. In this study, thermo-sensitivity has been introduced onto PET surfaces by graft copolymerization of NiPAAm. The PET surface was first photo-oxidized in the presence of H2O2, to have enriched concentration of -COOH groups which were later reacted with allylamine (AlAm) to introduce vinyl end groups at the surface. These groups were used as active sites for graft copolymerization of NiPAAm. The influences of solvent, monomer concentration and time on grafting have been investigated. Graft copolymerization was performed in air at room temperature by placing PET films into monomer solution which contains benzophenon as photoinitiator. For the most effective surface modification, parameters as monomer concentration (% 5- 15), photoinitiator amount (%5-20), UV excited time (1-4 hour) that effect the graft yield were investigated. In order to obtain desired surface property, % 10(w/w) monomer concentration, %10(w/w) benzophenone and 60 minutes irradiation time were determined as the optimum conditions. In addition to conventional polymerization, PET-g-NiPAAm surface was synthesized by RAFT-mediated graft polymerization in the presence of Cyanomethyl dodecyl trithiocarbonate based RAFT agent at 70 ºC under nitrogen atmosphere. % Grafting degree was calculated by using gravimetric method. The thickness of grafted layer can be adjusted by grafting reaction parameters via grafting degree and also confirmed by Ellipsometry. Imaging in water environment revealed the reversible modification of surface morphology below and above the LCST temperature of PNiPAAm. The grafted surfaces were analyzed by colorimetric assay, ATR-FTIR, Raman, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM EDX), XPS spectroscopies, Thermogravimetric analysis (TGA), and Differential scanning calorimetry (DSC). Number-average molecular weights (Mn) and dispersity indices of the polymers were determined by Gel Permeation Chromatography (GPC).