Polymer Layered-Silicate Nanocomposites from Thermally Stable Trialkyl-Imidazolium Treated Montmorillonite
Jeffrey W. Gilman, W H. Awad, Rick D. Davis, Cher H. Davis, John R. Shields, T E. Sutto, Richard H. Harris Jr., A B. Morgan, J H. Callahan, Paul C. Trulove, Hugh C. De Long
The limited thermal stability of alkyl ammonium cations and the processing instability of some polymers (polyamide-6 (PA-6) and polystyrene (PS)) in the presence of nanodispersed montmorillonite (MMT) has motivated the development of improved organophillic treatments for layered silicates. Success in this regard should enable preparation of polymer layered silicate nanocomposites from thermoplastic engineering polymers with high melt-processing temperatures, 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 preparation of nanocomposites. Several trialkyl- imidazolium 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 degrees C improvement in thermal stability (in N2) as compared to the alkylammonium treated MMT. The use of 1-alkyl-2,3-dimethylimidazolium salt in fluorinated synthetic mica (FSM) gives a 200 degrees 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.