Synthesis of lamellar isobutyl silicates and dispersion in polypropylene melts

A new synthetic clay, iC ₄-LMS, which is a lamellar mesostructured silicate with isobutyl groups covalently attached to silicate sheets, was synthesized with the goal to increase the compatibility of the inorganic sheets with polypropylene (PP) in a melt-blending process. The lamellar morphology of iC ₄-LMS was confirmed using X-ray diffraction and transmission electron microscopy. Based on ²⁹Si and ¹³C{ ¹H) CP-MAS NMR spectra, isobutyl functional groups were attached to at least 10 mol % of silicate tetrahedral sites in the inorganic layers. These surface groups mimic the subunits in the PP chains. Samples of iC ₄-LMS were mixed with several organic solvents and sonicated. The solvent most like PP, tetramethylpentadecane, had the highest viscosity, forming a gel which indicates very good dispersion of the clay. However, when iC ₄-LMS was melt-blended with PP, it did not show significant increase in rheology. This modest effect on rheology may arise from fracture of iC ₄-LMS layers as a result of the shear stresses during melt blending produced by the viscous PP.