講者：鄒海雄博士
演講題目：Poly(1-Octadecene) Molecular Bottlebrushes
演講時間：11/14(Tue) 2:00pm
演講地點：化工館 工223會議室
主持人：戴子安教授
Poly(1-Octadecene) Molecular Bottlebrushes
Andy Tsou, Carlos López-Barrón, Jarod Younker, Alex Norman, Jonathan Schaefer, and John Hagadorn
Global Chemical Research, ExxonMobil Chemical Company
Abstract
Isotactic and atactic poly(1-octadecene) (iPOD and aPOD) have been synthesized by organo-metallic coordinative insertion polymerization of 1-octadecene. Analyzing X-ray and neutron scattering data of POD melts identifies their bottlebrush structures as flexible rods where the rod length is the extended backbone length and rod radius is the side-chain coil dimension. Upon cooling, both iPOD and aPOD melts crystallize by fully extending their coiled side chains to form orthorhombic alkane crystals in iPODs and nematically ordered rotator alkane crystals in atactic PODs, as determined by X-ray scattering and Raman spectroscopy. Molecular dynamics simulations of isotactic and atactic 48-mers of 1-octadecene were applied to define and verify melt and crystalline structures and scattering peak assignments, respectively. Modeling suggests that side chains of both crystallized isotactic and atactic PODs align at 70 and 160 ° to the 4/1 spiral backbone of equal probability, at an average of 115 °, and POD chains pack in an anti-parallel pattern. Large wheat-sheaf structural assembly of fibril bundles can be observed in aPOD, thus renders it opaque. These fibrils may come from hexagonal packing of several bottlebrush POD rods. Similar fibril alignment and hexagonal packing of bottlebrush POD rods could be found during extensional flow and under contact pressure. Formation of surface assembled POD rods and corresponding reduction in contact friction were demonstrated using AFM (Atomic Force Microscopy) surface contact force measurements with colloidal probes.
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