RESUMEN
A novel polymer, poly(2-(N -carbazolyl)ethyl methacrylate) end-capped with fullerene (PCzMA-C(60) ), has been synthesized via living anionic polymerization. Electrically programmable flash memory devices were easily fabricated with this polymer by using solution coating and metal deposition. This polymer was found in these devices to exhibit bipolar and unipolar switching behaviors with a high ON/OFF current ratio, a long retention time, high reliability, and low power consumption. The excellent properties and easy processability of this polymer open up the possibility of the mass production of high performance nonvolatile memory devices at low cost.
Asunto(s)
Equipos y Suministros Eléctricos , Fulerenos/química , Polímeros/química , Ácidos Polimetacrílicos/química , Carbazoles/química , Modelos Moleculares , Conformación Molecular , Polímeros/síntesis química , Ácidos Polimetacrílicos/síntesis químicaRESUMEN
A rigorous molecular characterization of comb-shaped polystyrene (PS) was carried out taking advantage of its molecular structure, a normal hydrogenous backbone, and deuterated side chains. Normal phase LC (NPLC) can separate the comb PS species well according to their molecular weight. Nonetheless, it cannot distinguish the backbone from the side chains and the differently structured polymers having a similar molecular weight, e.g, a single backbone comb and a coupled backbone comb with fewer side chains. In contrast to NPLC, the hydrogenous polymer is retained longer than the deuterated counterpart in reversed phase LC (RPLC). When the isotope sensitivity of RPLC is taken advantage of, the comb PS is cross fractionated by NPLC and RPLC, and a two-dimensional mapping with respect to the backbone chain length and the number of branches is fully established.
RESUMEN
The retention behavior of deuterated polystyrene (d-PS) and normal hydrogenous polystyrene (h-PS) was investigated in normal phase (NP) and reversed phase (RP) liquid chromatography (LC). It was found that d-PS was retained slightly longer than h-PS in NPLC (bare silica column and tetrahydrofuran (THF)/n-hexane mixed mobile phase) while in RPLC (C18-bonded silica column and THF/methanol mixed mobile phase) h-PS was retained longer than d-PS. The retention behaviors are interpreted in terms of the thermodynamic variables associated with LC separations. The different retention behavior of deuterated polymers from that of hydrogenous polymers could allow separation of partially deuterated polymers according to the deuterium content, such as for copolymers in LC characterization.
RESUMEN
The liquid chromatographic retention of polystyrene (PS) oligomer was examined taking the column hold-up volume as an adjustable parameter based on the assumption that Martin's rule is valid, i.e., ln k (retention factor) is proportional to the degree of polymerization (DP). In both bare silica and C18-bonded silica columns, thus determined column hold-up volume is systematically smaller than the elution volume of the injection solvent. When the column hold-up volume was taken as an adjustable parameter, the retention of PS oligomer in organic mobile phase follows Martin's rule (ln k proportional, variant DP) near perfectly. In addition, the enthalpy and entropy changes associated with the solute transfer, determined from the temperature dependence of the PS oligomer retention, also show excellent linear dependence on the degree of polymerization if the adjustable column hold-up volume was used. When we compare the retention behavior of PS and hydroxyl terminated PS, the repeating (styrene) unit exhibits the same enthalpy and entropy change while the end group shows the corresponding difference. All observations conform to Martin's rule regardless of the columns used, but the physical nature of the adjustable column hold-up volume remains to be elucidated.