Development of Boron Cage Compound Nanocomposite Elastomers
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Development of Boron Cage Compound Nanocomposite Elastomers Eric A. Eastwood1, Daniel E. Bowen, III1, and Mark W. Lee, Jr.2 1 National Nuclear Security Administration’s Kansas City Plant, Honeywell Federal Manufacturing & Technologies, 2000 East 95th Street, Kansas City, MO 64141-6159 U.S.A. 2 University of Missouri–Columbia, Department of Radiology, International Institute of Nano and Molecular Medicine 1514 Research Park Drive, Columbia, MO 65211450, U.S.A. ABSTRACT A wide variety of nanofillers of varying compositions have been used to create polymer nanocomposites, including tubes, wires, fibers, sheets, and particles. A new class of compounds has been identified for use as nanofillers, boron cage compounds. Boron cage compounds are discrete, icosahedral closed cage molecules of high boron content and examples include carboranes and dodecaborate salts. Several chemically modified boron cage compounds have been incorporated into polyolefin elastomers, such as poly(ethylene-co-vinyl acetate), poly(ethylene-co-vinyl acetate-co-vinyl alcohol), poly(ethylene-co-ethyl acrylate), and poly(ethylene-co-octene), among others. The resulting thermal and thermomechanical properties were evaluated in order to determine when plasticization and reinforcement occur to better understand the chemical structure/physical property relationships. Materials with a wide range of properties were produced, however under certain conditions, advanced materials were created with high boron contents, improved thermal stability, mechanical strength, and significant reinforcement. INTRODUCTION Through the successful incorporation of nanofillers, polymer nanocomposites have demonstrated advanced material properties, including reinforcement, thermal, flame, moisture, and chemical resistance, barrier properties, and improved electrical properties, among others. The high surface area of nanofillers, and thereby their enhanced interaction with polymer chains, most certainly contributes to the observed properties [1]. Now boron cage compounds (BCCs) have been identified as a new class of compounds that can be used as nanofillers [2]. Collectively, BCCs are icosahedral closed cage, chemically modifiable molecules or ions of high boron content. These aromatic polyhedral boranes are highly stable, and include carboranes and dodecaborate salts [3]. One of our critical observations is that BCCs closely resemble other nanoparticles/molecules, such as polyhedral oligomeric silsesquioxanes (POSS) and C60 fullerene [4]. In particular, all three are discrete, rigid, closed cage, spherical, and 3-dimensional molecules of similar size (Figure 1). R
R
R X
R
R Substituted Carborane (Diameter = ~0.8-1.0nm)
O Si R Si O
O
O
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O
O SiO Si
O
Si
Si
O Si
O
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Si O
R
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POSS - Polyhedral Oligomeric Silsesquioxane (Diameter = ~0.9 - 1.2nm)
C60 Fullerene (Diameter = 1.1nm)
Figure 1. Comparison of substituted carborane, POSS, and C60 fullerene.
Although a few isolated cases serve as precedent, the synthesis, polymerization and copolymeriza
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