Graft copolymers having hydrophobic backbone and hydrophilic branches. XXIII. Particle size control of poly(ethylene glycol)-coated polystyrene nanoparticles prepared by macromonomer method

Monodisperse polymeric nanospheres, which consist of polystyrene cores and poly(ethylene glycol) (PEG) branches on their surfaces, were prepared by the dispersion copolymerization of styrene (St) with PEG macromonomers that had a methacryloyl (MMA-PEG) or p-vinylbenzyl (St-PEG) end group in various organic solvent/water media. Electron spectroscopy for chemical analysis (ESCA) of the nanosphere surfaces indicated that PEG macromonomer chains were favorably located on their surfaces. The morphologies of the nanospheres were observed via a scanning electron micrograph (SEM), and particle sizes were estimated by a submicron particle analyzer. When both the concentration of macromonomers and molecular weight were higher, small nanospheres in diameter were obtained. Larger nanospheres in diameter were obtained using macromonomers with low molecular weight at lower concentration. The functions that correlate the diameter (D_n) on different concentration units were D_n = K[St]^0.64[MMA-PEG]^{−0.53±0.01}[I]^−0.49 and D_n = K[St]^0.80[St-PEG]^{−0.69±0.01}[I]^−0.22, where [I], [St], [MMA-PEG], and [St-PEG] are initiator, styrene, MMA-PEG, and St-PEG macromonomer concentration in feed, respectively. When the reaction parameters such as the molecular weight of the macromonomers were properly chosen, the particle size could be controlled in a range from ca. 80 to 3100 nm. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2155–2166, 1999     

Photoluminescence and population analysis of single-walled carbon nanotubes produced by CVD and pulsed-laser vaporization methods

Band gap photoluminescence (PL) behaviors of single-walled carbon nanotubes (SWNTs) grown by the methods of chemical vapor deposition and pulsed-laser vaporization are investigated over the wide diameter range (≈0.8–1.4 nm). The peak intensity of the PL signals strongly depends on chirality and the ‘(2n + m) family type’ of SWNTs. Based on the PL results, a population analysis of these SWNTs is conducted by combining the calculated PL yields for each (n, m) tube. The results are directly compared with the histograms of diameter distributions estimated by the transmission electron microscope (TEM) observations to check the validity of the analysis.     

Methacrylic acid and methyl methacrylate oligomers adsorbed to porous isotactic poly(methyl methacrylate) ultrathin films and mechanistic studies of living template polymerization

Methacrylic acid (MAA), methyl methacrylate (MMA), methacrylamide, and oligomers of MAA and MMA were selected as a model of active radical species in living template polymerization using stereocomplex formation. The adsorption behaviors of the aforementioned model compounds were examined toward porous isotactic‐(it‐) poly(methyl methacrylate) (PMMA) ultrathin films on a quartz crystal microbalance, which was prepared by the extracting of syndiotactic‐(st‐) poly(methacrylic acid) (PMAA) from it‐PMMA/st‐PMAA stereocomplexes. The apparent predominant adsorption of oligomers to monomers was observed in both PMAA and PMMA oligomers, suggesting that the mechanism of template polymerization follows the pick up mechanism. Although vinyl monomers were not incorporated into the porous it‐PMMA ultrathin film, both PMMA and PMAA oligomers were adsorbed at the initial stages. However, adsorbed amounts were limited to about 5 and 15% at 0.1 mol L^?1, respectively, which are much smaller values than corresponding st‐polymers. The results imply that radical coupling reaction is prevented during template polymerization to support the resulting living polymerization. ATR‐IR spectral patterns of oligomer complexes and it‐PMMA slightly changed in both cases, suggesting complex formation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5879–5886, 2008     

Flow characteristics and spinnability of sols prepared from silicon alkoxide solution

Structural evolution of the solution of tetraethoxysilane hydrolyzed with [H₂O]/[Si(OC₂H₅)₄] = 2 under acidic condition has been investigated by rheological measurements. It was found that the solution behaves as a Newtonian liquid up to a highly viscous state and shows spinnability before gelation when the evaporation of the solvent is allowed during gelation reaction. On the other hand, the solution behaved as a non-Newtonian liquid in the viscous state, showing no spinnability when the evaporation of the solvent was not allowed during the reaction. It was indicated from the Casson plots that the spinnable solution prepared in the open system has no yield stress up to highly viscous states, whereas the non-spinnable solution prepared in the closed system has a yield stress at viscous states. It was proposed that the increase in viscosity of the open system solution is attributable to the concentration of the sol particles whereas that of the closed system solution is attributable to the formation of the three dimensional network in the solution.     

Specific thermosensitive volume change of biopolymer gels derived from propylated poly(γ-glutamate)s

Thermosensitive biopolymers with an amphipathic structure were synthesized through the propyl esterification of the carboxyl groups of poly(γ-glutamic acid) (γ-PGA). The clouding temperature on heating was controlled by the addition of different amounts of NaCl and by the degree of esterification. The clearing temperature on cooling was independent of the aqueous milieu, presumably because of the strong multiple hydrogen bonds between the polymer chains formed in the collapsed state. The hydrogel of γ-PGA propylate crosslinked by a chemical reaction with hexamethylene diisocyanate also showed pH-responsive and thermoresponsive shrinking, but the volume recovery was incomplete during the cooling process. A Fourier transform infrared/attenuated total reflection study showed that the incomplete volume recovery might be associated with the amide hydrogen bonding being strengthened by the chemical crosslinkage. The addition of urea made the volume change complete. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4492–4501, 2004     

Pressure and temperature history in diamond silicon mixtures during dynamic compaction

Diamond powders with silicon additives were shock compressed by using a flyer impact technique. Pressure and temperature histories in the powder mixtures were numerically simulated in order to determine the optimum experimental condition which resulted in the highest Vicker's hardness. This was found to be: an initial diamond particle size of 2–4m at 7.2 % silicon by volume. The results of the simulations were consistent with the distribution of the microstructure and the microhardness in the compact.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Kinetics and mechanism of H+(aq)-assisted aquation of [Cr(N3)(S-pdtra)]− and [Cr(N3(edtrp)]−ions

Two new complex anions, [Cr(N3)(S-pdtra)]– and [Cr(N3)(edtrp)]–, were obtained in solution by N3–/HN3 anation of the aqua analogues (S-pdtra = S-propane-1,2-diamine-N,N,N-triacetate, edtrp = ethylenediamine-N,N,N-tripropionate). Aquation of these species in acidic media leads to the same geometrical isomers as those used for the synthesis. The aquation rate is strongly dependent upon [H] and is substantially higher in D2O than in H2O. Protonation of the coordinated azide was not observed spectrophotometrically. The rate law and activation parameters have been determined and discussed.