Min Chul Suh

Electrochemical insertion of lithium into polyacrylonitrile-based disordered carbons

Electrochemical lithium insertion into polyacrylonitrile (PAN)-based disordered carbons was studied using the techniques of discharge/charge tests, cyclic voltammetry, and {sup 7}Li nuclear magnetic resonance (NMR) spectroscopy. The PAN-based carbons were prepared by vacuum pyrolysis of PAN at 500, 800, and 1,000 C. They showed charge capacities between 254 and 380 mAh/g in the first cycle. {sup 7}Li NMR spectra showed two kinds of lithium insertion sites in the PAN-based carbons: a reversible site where lithium is removed in the subsequent charge process and an irreversible site where lithium remains intact. The NMR results suggest that lithium in fully Li-inserted PAN-based carbons has an ionic character, and reversible site lithium resides between negatively charged carbon layers.

Lithium Insertion into Disordered Carbons Prepared from Organic Polymers

Disordered carbon samples were prepared from four organic polymers: poly[(Z)-1-methoxy-4-phenyl-1-buten-3-yne, [poly(MPBEY)], poly(1,4-diphenyl-1-buten-3-yne) [poly(DPBEY)], poly[5-(2-pyridyl)-2,4-pentadiyn-1-ol] [poly(PyPDO)], and poly(2,4-hexadiyn-1,6-diol) (PHDO). Electrochemical lithium insertion into these disordered carbons was studied with discharge/charge tests, cyclic voltammetry, and 7 Li nuclear magnetic resonance (NMR) spectroscopy. In the potential range of 0.0 to 2.5 V vs. Li/Li + , all carbons showed discharge/charge curves with a hysteresis effect unlike typical curves for standard lithium insertion/removal processes in pyrolyzed carbons. This hysteresis may be caused by the lithium-oxygen bonding of the organolithium complexes. 7 Li NMR spectra showed two kinds of lithium insertion sites in all carbons: a reversible site from which lithium could be removed in the subsequent charge process and an irreversible site where lithium remains intact. The NMR results suggest that the reversible site lithium has ionic nature in all of the fully Li-inserted carbons.

Photoconductivity of 3,5‐dinitrobenzoate of poly[1‐phenyl‐1‐penten‐3‐yn‐5‐ol] (DN‐PPPYO) blended with poly[4‐(p‐N,N‐diphenylaminophenyl)‐1‐phenyl‐1‐buten‐3‐yne] (PPAPBEY) as a hole transporting polymer

The 3,5-dinitrobenzoate of poly[1-phenyl-1-penten-3-yn-5-ol] (DN-PPPYO) blended with a charge transporting polymer, poly[4-(p-N,N-diphenylaminophenyl)-1-phenyl-1-buten-3-yne] (PPAPBEY), and polystyrene shows high photoconductivity due to the high concentration of the triphenylamine (TPA) moiety and the fully conjugated backbone as verified by xerographic measurements.

Synthesis and properties of new SiH‐containing polymers

Poly[(methylsilylene)ethynylene] (1) and poly[2,5-thiophenediyl(methylsilylene)] (2) are prepared in good yields. Thermogravimetric analysis and differential scanning calorimetry indicate the Si-H group to increase the pyrolysis residue yields. Gelation was achieved from polymer 1 to get improved preceramic materials.

Preparation of graphite-like polymers from 1,3-diacetylenes: Pyrolytic poly[1-(2-methoxyphenyl)penta-1,3-diyn-5-ol]

Abstract Poly[1-(2-methoxyphenyl)penta-1,3-diyn-5-ol] [(1,2)-PMDO] was prepared by NbCl 5 /(n-Bu) 4 Sn catalyzed metathesis of (1,2)-MDO followed by spin-casting in methylene chloride. Thin films of resulting polymers were pyrolyzed at various temperatures. UV, IR, and Raman spectroscopic studies were carried out to determine the chemical structure of the films during pyrolysis. The electrical conductivity of the films could be varied on cabonization at different temperatures.

Microstructure and electrochemical properties of some synthetic carbons

Four kinds of synthetic carbons were prepared by vacuum pyrolysis of black polyacene-based polymers: poly[(Z)-1-methoxy-4-phenyl-1-buten-3-yne]-750 [poly(MPB EY)-750], poly(1,4-diphenyl-1-buten-3-yne)-750 [poly(DPBEY)-750], poly[5-(2-pyridyl)-2,4-pentadiyn-1-ol]-800 [poly(PyPDO)-800], and poly(2,4-hexadiyn-1,6-diol)-800 (PHDO-800). The carbonization yields and electrochemical properties of carbons were dependent on precursor polymers. The relationship between the structure of synthetic carbons and electrochemical behavior was investigated by transmission electron microscopy (TEM), discharge/charge tests and cyclic voltammetry studies. Precursor polymers from enynes yielded synthetic carbons with many defect sites. Poly(DPBEY)-750, poly(PyPDO)-800, and PHDO-800 show smaller charge capacities than graphite (372 mA h/g), while a large charge capacity of 496 mA h/g is observed from poly(MPBEY)-750 in the first cycle. Poly(PyPDO)-800 displays very large capacity on cyclic voltammetry tests compared to other carbon samples indicating that the kinetics of lithium insertion/deinsertion in poly(PyPDO)-800 is faster than those of other carbons.

Nonlinear optical and electrical properties of poly[1-(2-methoxyphenyl) penta-1,3-diyn-5-ol]

Abstract Poly[1-(2-methoxyphenyl)penta-1,3-diyn-5-ol] ((1,2)-PMDO) was prepared by NbCl 5 (n-Bu) 4 Sn -catalyzed metathesis. The 2:3 (1,2)-PMDO/poly(methyl methacrylate) (wt./wt.) film showed a conductivity of about 10 −3 S/cm after ferric chloride (FeCl 3 ) doping. Third-order nonlinear optical susceptibility ( χ (3) ) of (1,2)-PMDO was evaluated from third-harmonic generation by the Maker fringe method.

Photoconductivity of modified poly(vinyl esters)

Poly(vinyl cinnamate) (PVA-C) doped with 2,4-dinitroaniline (24DNA) or triphenyl amine (TPA) shows high photoconductivity. Poly[(vinyl cinnamate)-co-(vinyl 3,5-dinitrobenzoate)] (PVA-CD) and poly[ethylene-co-(vinyl cinnamate)-co-(vinyl 3,5-dinitrobenzoate)] (PVA-ECD) are highly photoconductive even in the absence of dopants such as 24DNA.

Photoconducting behavior of 3,5-dinitrobenzoate of poly [1- (n-methoxyphenyl) penta-1,3-diyn-5-ol]

Abstract 3,5-Dinitrobenzoates of poly[1-( n -methoxyphenyl)penta-1,3-diyn-5-ol] (DN-1, n -PMDO ( n = 2, 4)) are prepared by the reaction of (1, n )-PMDO ( n = 2, 4) and 3,5-dinitrobenzoyl chloride. DN-1,2-PMDO shows high initial potential and low conductivity, while DM-1,4-PMDO shows low initial potential and high photoconductivity. The photoconductivity of DN-1,2-PMDO could be improved by introducing charge transport materials like triphenylamine.

Polymerization of 2,4-hexadiyn-1,6-diol by chemical vapor deposition

2,4-Hexadiyn-1,6-diol (HDO) was polymerized on glass and silicon plates by chemical vapor deposition without transition metal catalysis to form homogeneous thin films. Structural properties of the films were investigated by FT-IR, UV-visible, Raman, x-ray diffraction, and XPS spectroscopic analyses. The structure of CVD-polymerized HDO (CVD-PHDO) films was different from that of metathesis polymerized HDO (metathesis-PHDO), showing a polyacene-based structure but no polyene structure with acetylenic side groups.