Synthesis of polycarbonate-layered silicate nanocomposites via cyclic oligomers

A partially exfoliated bisphenol A polycarbonate nanocomposite has been prepared by using carbonate cyclic oligomers and ditallow dimethyl exchanged montmorillonite (B34). Wide-angle X-ray diffraction (WAXD) indicated that exfoliation of this organically modified layered silicate (OLS) occurs after mixing with the cyclic oligomers in a brabender mixer for 1 h at 180 degrees C. Subsequent ring-opening polymerization of the cyclic oligomers converted the matrix into linear polymer without disruption of the layer dispersion. Transmission electron microscopy revealed that a partially exfoliated structure was obtained, although no indication of layer correlation was observed in WAXD. if linear polycarbonate was similarly treated with B34 in a brabender mixer, only an intercalated hybrid was obtained. Furthermore, conventional melt or solution processing of the B34 with either linear polycarbonate or cyclic oligomers yielded intercalated nanocomposites with interlayer spacings of 3.27 and 3.6-3.8 nm, respectively. These results demonstrate that consideration of molecular architecture (cyclic vs linear) and kinetics (medium viscosity and shear) is critical for nanocomposite formation.