| Polyhedral Oligomeric Silsesquioxane (POSS) is a three-dimensional structurally well-defined cage-like molecule represented by formula (RSiO 1.5)n (n = 6, 8, 10 or higher, R is an organic group). POSS macromers have an inorganic silica-like core, which is surrounded by organic groups, and the physical size of the POSS cage is about 1.5 nm. Because of their hybrid nature and nanometer-scale feature, as shown in this study, POSS macromers were dispersed in a molecular level into polymeric systems by blending, in effect achieved POSS/Polymer nano-blends. The POSS macromers used in this work were cubic-caged POSS macromers bearing different organic corner groups. Polystyrene (PS) and polydimethyl siloxane (PDMS) were used as model polymers.; The investigations involved in this work include two parts. In the first part, the microstructures and thermal properties of the POSS macromers were investigated by using X-ray diffractometer, Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). In the second part, the morphologies of POSS/Polymer blends were examined using Transmission Electronic Microscopy (TEM), and X-ray diffractometer. Their thermal and rheological properties were studied with DSC, TGA, and Rheometer.; The results of this work showed that different corner groups on the POSS cage affected the morphological structures and properties of the POSS macromers. The higher the degree of the symmetry and regularity of the POSS macromers and the smaller the size of the corner groups, the more ordered the POSS macromers. The POSS macromers with functionalities, which may undergo chemical cross-linking reactions, possessed high thermal stabilities.; The morphology studies of POSS/PS and POSS/PDMS blends showed that depending on the attached organic groups on the POSS cages, the structures of the polymer matrix and the composition of the blends, the morphologies of the POSS/polymer blends ranged from complete separation to homogeneous dispersion in the nanoscopic scale.; The rheological investigations of the POSS/PDMS blends revealed that under elevated temperatures, gelation occurred in the POSS/PDMS blends as a result of intermolecular association between POSS nano-fillers and PDMS polymer chains. The formation of gel exhibited a solid-like behavior, which in turn showed a significantly improved creep resistance. Since the formation of gel relates with only physical interaction, the POSS/PDMS gel can be destroyed under large stain/stress and re-formed under elevated temperatures. |
