A novel single lithium-ion (Li-ion) conducting polymer electrolyte is presented that is composed of the lithium salt of a polyanion, poly[(4-styrenesulfonyl)(trifluoromethyl(S-trifluoromethylsulfonylimino)sulfonyl)imide] (PSsTFSI(-)), and high-molecular-weight poly(ethylene oxide) (PEO). The neat LiPSsTFSI ionomer displays a low glass-transition temperature (44.3 °C; that is, strongly plasticizing effect). The complex of LiPSsTFSI/PEO exhibits a high Li-ion transference number (tLi (+) =0.91) and is thermally stable up to 300 °C. Meanwhile, it exhibits a Li-ion conductivity as high as 1.35×10(-4) S cm(-1) at 90 °C, which is comparable to that for the classic ambipolar LiTFSI/PEO SPEs at the same temperature. These outstanding properties of the LiPSsTFSI/PEO blended polymer electrolyte would make it promising as solid polymer electrolytes for Li batteries.
Novel organic/inorganic hybrid copolymers have been prepared using single site catalysis.
Ethylene copolymers incorporating a norbornylene-substituted polyhedral oligomeric silsesquioxane
(POSS) macromonomer have been prepared using a metallocene/methylaluminoxane (MAO) cocatalyst
system. Isotactic polypropylene-containing POSS nanoparticles were also synthesized for the first time
using a similar approach utilizing a C
2 symmetric ansa-metallocene. A wide range of POSS concentrations
were obtained in these polyolefin POSS copolymers under mild conditions, up to 56 wt % for PE-POSS
copolymers and 73 wt % for PP-POSS copolymers. Initial findings point to improved thermooxidative
stability for these nanocomposite polyolefins containing the “molecular silica” side groups relative to their
homopolymer analogues. Thermogravimetric analysis of the PE-POSS copolymers under air shows a 90
°C improvement, relative to a polyethylene control sample of similar molecular weight, in the onset of
decomposition temperature based upon 5% mass loss. On the basis of dynamic mechanical thermal
analysis, the tensile properties of the PE-POSS copolymer were maintained at low POSS loadings. A
modulus plateau at temperatures above 175 °C is observed, indicating suppression of melt flow for
polyethylene POSS copolymers.
A novel nanocomposite containing polyethylene and polyhedral oligomeric silsesquioxane
(POSS) nanoparticles has been characterized using wide-angle X-ray scattering (WAXS). In copolymers
formed between ethylene and POSS containing macromonomers, the POSS units, attached as pendant
groups off the polyethylene backbones, are found to aggregate and crystallize as nanocrystals. The POSS
nanoparticles in such PE-co-POSS copolymers form a lattice separate from the PE lattice with
characteristic diffraction signals. From both line broadening of the diffraction maxima and also the oriented
diffraction in a drawn material, we conclude that POSS crystallizes as anisotropically shaped crystallites.
The presence of POSS disrupts the crystallization of polyethylene and results in less and smaller/disordered
polyethylene crystallites. POSS nanocrystals are covalently connected to the PE crystallites via an
intermediate disordered interfacial region. The PE crystallites are reinforced by the POSS crystallites,
maintaining their crystalline structure under high draw ratio. In total, these contributions help to explain
the novel properties of this type of nanocomposite, such as better dimensional stability, extension of
high-temperature rubbery plateau, and strong thermal oxidative resistance.
A novel polymeric shape memory system of chemically cross-linked polycyclooctene (PCO) was developed and characterized. PCO was synthesized via ring-opening metathesis polymerization of cyclooctene using the dihydroimidazolylidene-modified Grubb's catalyst. After dicumyl peroxide was added to PCO, the mixture was compression-molded into a film and further cured through chemical crosslinking upon heating. The chemically cross-linked PCO samples were fully characterized using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and wide-angle X-ray scattering (WAXS) in order to gain insight into the rapid shape memory behavior. We observe that the transition temperature of PCO is tunable through the change of the trans/cis ratio of vinylene groups. A fast shape memory behavior was observed, where the primary stress-free shape was recovered within 1 s on immersion in hot water above the melting point of the crystalline PCO phase. In contrast with glassy shape memory polymers, chemically cross-linked PCO behaves as an elastomer capable of arbitrary shaping above the sharp melting temperature of the PCO crystalline phase and subsequent shape fixing during crystallization.
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