Poli(Etilen-Alt-Tetrafloroetilen) (Etfe) Ardışık Kopolimer Filmine Raft Yöntemi Ve Radyasyon Kullanılarak Stiren Aşılanması ve Yakıt Pili Membranı Hazırlanması

Abstract

Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization is applied to radiation-induced grafting of styrene onto ETFE. By sulfonation of the obtained graft-copolymer films, polymer electrolyte membranes have been prepared. Copolymer films were prepared by grafting of styrene onto ETFE by using cumyl phenyldithioacetate (CPDA) RAFT agent and after sulfonation structure of membranes were confirmed by ATR-FTIR Spectroscopy, Raman, Xray photoelectron spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX), thermogravimetric analysis and differential scanning calorimetry (TGA, DSC). In order to show homogeneous grafting with RAFT method, grafting reactions were performed with and without RAFT agent and surfaces of obtained graft-copolymer films were analyzed with atomic force microscopy (AFM). Grafted films prepared with RAFT method has shown more homegeneous surfaces with low roughness values. Effect of grafting and sulfonation processes on pore sizes of grafted films and membranes were investigated with positron annihilation lifetime spectroscopy (PALS). PALS study showed that grafting occur at amorphous region of ETFE film and pore sizes of the amorphous region decreases with grafting and sulfonation reactions. Glass transition temperature and mechanical properties of grafted films and membranes were investigated with dynamic mechanical analysis (DMA) and increase in glass transition temperature with increasing graft ratio was found. In order to obtain information about molecular weights of grafted chains and to show molecular weight control, grafting reactions with 9-131 % graft ratio were performed with and without RAFT agent and homopolymers obtained from reaction medium were characterized with size exclusion chromatoraphy (SEC). Molecular weight changes with total monomer conversion and polymers with low molecular weight distribution (generally Mw/Mn ˂1.25) were obtained with RAFT mediated grafting reactions. There is no molecular weight control for polymers obtained without RAFT agent and their molecular weight distribution is narrow. Ion exhange capacity (IEC) and proton conductivity of membranes prepared with RAFT mediated polymerizations were determined. Above 22 % graft ratio, high enough ion exchange capacity is obtained to be used as polymer electrolyte membrane. Ion exchange capacity of Nafion 112 is 0,91 which is 1,18 for ETFE-g-PSSA membrane with 22 % graft ratio prepared in this study. Proton conductivity values increases with graft ratio and very high proton conductivity was obtained for membrane with 48 % graft ratio (~ 150 mS.cm-1). Proton conductivity of Nafion 112 is 82 mS.cm-1.