ABSTRACT
The zero shear melt viscosity, eta0, for a variety of dendritic poly(benzyl ether) macromolecules has been measured. The viscosity of low generation dendrimers exhibits a strong molecular mass, M, dependence, yet, direct proportionality between eta0 and M is observed at higher generations. The viscosity scales with M for mono- and tridendrons rather than generation number. Hypercore dendrimers continue this scaling although the viscosity is slightly greater. A large deviation from the master curve for the mono- and tridendrons is found for an end-substituted monodendron. The viscosity for the end-substituted monodendron is also much more temperature dependent than virgin dendrimers, and it is concluded that end groups have a much larger effect on the viscosity than the core. Reexamination of literature data for intrinsic viscosity and glass transition temperature is performed, and these quantities also scale with molecular mass. Comparison with free volume theory indicates that the theory is extremely robust although some question of its validity is made when applied to dendrimers.
ABSTRACT
To obviate the destructive interaction of highly reactive metallocene catalysts with classical silica-based supports while retaining the advantage of supported catalysts, a noninteracting polystyrene support was developed. Supported catalysts for the polymerization of alpha-olefins are prepared by treating lightly cross-linked, chloromethylated polystyrene beads consecutively with a secondary amine, an ammonium salt of a weakly coordinating anion, and a neutral dialkylmetallocene. Catalytic sites are distributed homogeneously throughout the support particle, and the polymerization occurs within the bead, in contrast to traditional surface-supported metallocene catalysts. The copolymerization of ethylene and 1-hexene at 40 degreesC affords discrete spherical polyolefin beads with a size (0.3 to 1.4 millimeters) that varies according to the polymerization time.
ABSTRACT
The preparation and analysis of inorganic-organic polymer nanocomposites consisting of inorganic nanowires and multiwire "cables" in a random-coil organic polymer host is reported. Dissolution of inorganic (LiMo3Se3)n wires in a strongly coordinating monomer, vinylene carbonate, and the use of a rapid polymerization in the presence of a cross-linking agent produce nanocomposites without phase separation. Polymerization of dilute solutions yields a material containing mostly (Mo3Se3(-))n mono- and biwires, 6 to 20 angstroms in diameter and 50 to 100 nanometers long. Polymerization of more concentrated liquid crystalline solutions yields a nanocomposite containing oriented multiwire cables, 20 to 40 angstroms in diameter and up to 1500 nanometers long, that display optical anisotropy and electrical conductivity.
