Polymer/Layered Silicate Nanocomposites from Thermally Stable Trialkylimidazolium-Treated Montmorillonite

Abstract

The limited thermal stability of alkylammonium cations intercalated into smectite minerals (e.g., montmorillonite, MMT) and the processing instability of some polymers [polyamide-6 (PA-6) and polystyrene (PS)] in the presence of nanodispersed MMT have motivated the development of improved organophillic treatments for layered silicates. Success in this regard should enable the preparation of polymer/layered silicate nanocomposites from thermoplastic polymers that require high melt-processing temperatures or long residence times under high shear and from thermoset resins with high cure temperatures. Our efforts to address some of these issues focus on the use of new thermally stable imidazolium-treated layered silicates for the preparation of nanocomposites. Several trialkylimidazolium salt derivatives were prepared with propyl, butyl, decyl, and hexadecyl alkyl chains attached to the imidazolium through one of the nitrogens. These imidazolium salts were used to prepare the corresponding treated layered silicates. We report here that the use of 1-alkyl-2,3-dimethylimidazolium salts to replace the sodium in natural MMT gives organophillic MMT with a 100 °C improvement in thermal stability (in N 2 ) as compared to the alkylammonium-treated MMT. The use of 1-alkyl-2,3-dimethylimidazolium salt in fluorinated synthetic mica (FSM) also gives a 100 °C improvement in thermal stability. The use of 1,2-dimethyl-3-hexadecylimidazolium-treated MMT gives an exfoliated PA-6 nanocomposite and, depending on processing conditions, either a partially exfoliated or an intercalated polystyrene nanocomposite.