The Synthesis of Liquid Crystalline Polymer on Gold Nanoparticles
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The Synthesis of Liquid Crystalline Polymer on Gold Nanoparticles Qinghong Fu, Thomas A. P. Seery Institute of Materials Science, University of Connecticut, 97 North Eagleville Road, Storrs, CT06269-3136 ABSTRACT Gold nanoparticles with thiol stabilizing layers were prepared with various fractions of end-functional thiols. Alcohol end-groups were further elaborated to norbornyl moieties so that a ruthenium alkylidene initiator could be tethered to the nanoparticle surfaces. In two different nanoparticle formulations the functional thiols possessed hydrocarbon chains that held the metal centers either near to or far from the surface of the thiol stabilizing layer. The tethered organometallic complexes were used to initiate polymerization from the nanoparticle surfaces. Liquid crystalline polymer was grown from nanoparticles where the metal center was tethered far from the surface but polymerization could not be initiated when the metal centers were held close to the surface. We hypothesize that steric hindrance is controlled by the length of the tethering thiol. Polarized optical microscopy showed that the polymer coated gold nanoparticles could still form a nematic mesophase at elevated temperature although the orientation of mesogens is restricted by crowding at the nanoparticle surface. Samples of unbound polymer were also prepared and exhibited similar transition behavior. INTRODUCTION Studies on side-chain liquid crystalline polymers (SCLCPs) with the mesogen laterally attached to the polymer backbone have been reported since the middle of 1980’s1-7. It couples the advantages of liquid crystals and classic polymeric materials. In addition, the mesogenic units can orient with different angles to the backbone resulting in different backbone morphologies. Laterally attached SCLCPs exhibit a range of mesogen orientations providing a variety of nematic and smectic morphologies. In the limiting cases, mesogens oriented parallel to the polymer backbone form nematic mesophases, while a perpendicular orientation leads to the smectic mesophase. Pugh and coworkers have reported a series of SCLCPs produced by chain growth processes where the mesogen was laterally attached to a norbornene monomer and polymers were formed by ring-opening metathesis polymerization (ROMP)1, 6-7. These SCLCPs form nematic mesophase in their pure state, and smectic mesophases were induced by addition of immiscible components. A large body of work has been produced on the influence of different monomer components that demonstrates how a great many properties can be tuned for this family of LCPs. Here we report the first data on the liquid crystalline structures and properties of SCLCPs that were chemically bound to surfaces. In this study, a SCLCP was grown from the catalyst sites on gold nanoparticles surfaces. The hybrid formed with liquid crystalline polymer brush covered on gold nanoparticles was observed under polarized optical microscope under elevated temperature. EXPERIMENTAL Synthesis of 5-Norbornene-2-Carbonyl Chloride 20mL 5-Norbornene-
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