Development of polymeric electrolytes for fuel cells: Synthesis and characterization of new sulfonated polystyrene-co-acrylonitrile-co-butyl acrylate terpolymers

Abstract

To improve the physical and chemical properties of styrene-derived polymers, new polystyrene-co-acrylonitrile-co-butyl acrylate terpolymers were synthesized and subsequently sulfonated. Six terpolymer compositions were prepared under mass radical polymerization conditions and further sulfonated to promote proton conductivity. The terpolymers were characterized by Fourier Transformed Infrared Spectroscopy (FTIR), proton and carbon nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR), Gel Permeation Chromatography (GPC), Thermomechanical Analysis (TMA), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Electrochemical Impedance Spectroscopy (EIS). All synthesized terpolymers have molecular weights over 160,000 g/mol and solubility on several organic solvents. Terpolymers also showed high thermal stability by TGA and comonomers reduced Tg transitions and complex moduli along BuA content; the complex moduli clearly increased with ACN content. Intermediate aliquots taken during the sulfonation reaction were characterized indicate that incorporation of the sulfonic group decreases the thermal stability from over 350 °C in terpolymers down to 150 °C after sulfonation. The degree of sulfonation analyzed by TGA ranged between 11.2 and 15.9% leading to a proton conductivity interval from 2.9 to 4.0 mS/cm. The results suggest a lateral crosslinking reaction through sulfone groups. The proton ion conductivity values obtained are similar to those of commercially available membranes described in the literature.