Interactions between Nafion resin and protonated dodecylamine modified montmorillonite: A solid state NMR study

Abstract

A series of nanocomposites have been prepared from perfluorosulfonylfluoride copolymer resin (Nafion) and layered montmorillonite (MMT) modified with protonated dodecylamine by conventional sol–gel intercalation. The structure of these nanocomposite materials have been characterized using FT-IR, elemental analysis, XRD and solid state NMR techniques, including 19F magic-angle spinning (MAS) NMR, 19F NMR relaxation time measurements, 29Si MAS, 1H MAS, 1H- 13C cross-polarization magic-angle spinning (CPMAS), and 1H- 13C heteronuclear correlation (HETCOR) 2D NMR. The results showed that thermal stability of Nafion was improved moderately by the addition of dodecylamine modified MMT without intercalation. FT-IR and 29Si MAS NMR results indicated that dodecylamine modification did not result in obvious changes in the MMT lattice structure. The XRD results showed that the protonated dodecylamine has been embedded and intercalated into the MMT interlayers, whereas Nafion was not. Elemental analysis results also suggested that some dodecylamine was adsorbed on the surface of MMT. 1H- 13C HETCOR 2D NMR experiment clearly indicated that strong electrostatic interactions were present between the NH + 3 group of dodecylamine and the fluorine-containing groups ( CF 3, OCF 2, and SCF 2) of Nafion resin. Such electrostatic interactions are probably the major contributors for the improved thermal stability of the resultant composite materials.