No abstract

The radical polymerizations of N‐alkylacrylamides, such as N‐methyl‐(NMAAm), N‐n‐propyl‐(NNPAAm), N‐benzyl‐(NBnAAm), and N‐(1‐phenylethyl)acrylamides (NPhEAAm), at low temperatures were investigated in the absence or presence of hexamethylphosphoramide (HMPA) and 3‐methyl‐3‐pentanol (3Me3PenOH), which induced the syndiotactic specificities in the radical polymerization of N‐isopropylacrylamide (NIPAAm). In the absence of the syndiotactic‐specificity inducers, the syndiotacticities of the obtained polymers gradually increased as the bulkiness of the N‐substituents increased. Both HMPA and 3Me3PenOH induced the syndiotactic specificities in the NNPAAm polymerizations as well as in the NIPAAm polymerizations. The addition of 3Me3PenOH into the polymerizations of NMAAm significantly induced the syndiotactic specificities, whereas the tacticities of the obtained polymers were hardly affected by adding HMPA. In the polymerizations of bulkier monomers, such as NBnAAm and NPhEAAm, HMPA worked as the syndiotactic specificity inducer at higher temperatures, whereas 3Me3PenOH hardly influenced the stereospecificity, regardless of the temperatures. The phase‐transition behaviors of the aqueous solutions of poly(NNPAAm)s were also investigated. It appeared that the poly (NNPAAm) with racemo dyad content of 70% exhibited unusual large hysteresis between the heating and cooling processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4575–4583, 2008

We report comprehensive studies of the crystallographic, magnetic, and thermal properties of a spinel-type magnetically frustrated compound, CoAl 2 O 4 , and a magnetically diluted system, Co 1 -x Zn x Al 2 O 4 . These studies revealed the effects of dilution and disorder when the tetrahedral magnetic Co ion was replaced by the nonmagnetic Zn ion. Low-temperature anomalies were observed in magnetic susceptibility at x < 0.6. A multicritical point was apparent at T = 3.4 K and x = 0.12, where the antiferromagnetic, spin-glass-like, and paramagnetic phases met. At that point, the quenched ferromagnetic component induced by a magnetic field during cooling was sharply enhanced and was observable below x = 0.6. At x ∼ 0.6, magnetic susceptibility and specific heat were described by temperature power laws, χ ∼ C/T ∼ T −δ , in accord with the site percolation threshold of the diamond lattice. This behavior is reminiscent of a quantum critical singularity. We propose an x-temperature phase diagram in the range 0 x 1 for Co 1 -x Zn x Al 2 O 4 . The transition temperature of CoAl 2 O 4 determined from magnetic susceptibility measured under hydrostatic pressure increased with increasing pressure.

[1] The SS-520-2 sounding rocket skimmed over the high-latitude part of the cusp region and observed fine-scale field-aligned electron precipitations in the vicinity of the inverted-V structures with the Low Energy Particle-Electron Spectrum Analyzer (LEP-ESA). There are at least two types of fine-scale electron precipitations, namely ''edge-type electron bursts'' and ''multiple energy-time dispersions.'' Edge-type electron bursts were observed only at the edge of the inverted-V region, whereas multiple energy-time dispersions were observed separately from the inverted-V region as well as within or overlapping it. The latter was characterized by field-aligned precipitations with falling energies from $200 eV down to $20 eV at a repetition rate of 1-2 Hz. Source altitudes were estimated using the energy-time and pitch angle-time dispersions. As a result, we found that the source altitudes were distributed along the geomagnetic field at altitudes of several thousand kilometers, depending on the accelerated energies of electrons. Higher-energy electrons are generated at higher altitudes. The source temperature of the energy-time dispersion was much higher than that of ionospheric cold electrons. We suggest that electrons injected from the magnetosheath were accelerated by inertial Alfvén waves at altitudes of several thousands of kilometers.

The radical polymerizations of N‐isopropylacrylamide (NIPAAm) were carried out in toluene at low temperatures in the presence of phosphoric acid esters such as trimethyl phosphate, triethyl phosphate (TEP), tri‐n‐propyl phosphate, and tri‐n‐butyl phosphate (TBP). Syndiotactically rich poly(NIPAAm)s were obtained from −60 to 0 °C, and TEP provided the highest syndiotacticity (racemo dyad = 65%) at −40 °C. On the other hand, lowering the temperature reversed the stereoselectivity of the propagation reaction so that isotactically rich poly(NIPAAm)s were obtained at −80 °C. In particular, TBP exhibited the most isotactic specificity (meso dyad = 57%). Job's plots for NIPAAm–TBP mixtures revealed that NIPAAm and TBP formed a 1:1 complex at 0 °C and a predominantly 1:2 complex at −80 °C through a hydrogen‐bonding interaction. Therefore, the stereospecificity of NIPAAm polymerization should depend on the stoichiometry of the hydrogen‐bond‐assisted complex. Thus, the mechanism for this polymerization system was discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 50–62, 2005