Chemo-, regio-, and stereo-selective perfluoroalkylations by a Grignard complex with zirconocene.

The synthesis of highly reactive perfluoroalkyl Grignard reagents with early transition metal zirconocene complexes and their new types of highly chemo-, regio-, and stereo-selective perfluoroalkylation reactions are reported with epoxides in particular. The zirconocene complex is advantageous in activating the perfluoroalkyl Grignard species. The zirconocene·Grignard complexes were clarified by DOSY. Both (1)H and (19)F DOSY analyses show that the addition of MAO and dioxane to the mixture of RFMgCl and Cp2ZrCl2 connects Cp2Zr and RFMg to generate the zirconocene/perfluoroalkyl-Grignard/dioxane complex.

NMR Relaxometry for the Thermal Stability and Phase Transition Mechanism of Flower-like Micelles from Linear and Cyclic Amphiphilic Block Copolymers.

Linear and cyclic amphiphilic block copolymers consisting of poly(ethylene oxide) (PEO) as the hydrophilic segment and poly(methyl acrylate) or poly(ethyl acrylate) as the hydrophobic segments were synthesized and self-assembled to form flower-like micelles. The micelles from linear (methyl acrylate)12(ethylene oxide)73(methyl acrylate)12 (Mn = 1000-3200-1000, l-MOM) showed a cloud point (Tc) at 46 °C by the transmittance of the micellar solution, whereas that of cyclic (methyl acrylate)30(ethylene oxide)79 (Mn = 2600-3500, c-MO) increased to 72 °C, as previously reported. DLS showed comparable diameters (l-MOM, 14 nm; c-MO, 12 nm) and Tc values (l-MOM, 48 °C; c-MO, 75 °C). For the investigation of the difference in Tc and the phase transition mechanism based on the polymer topology, NMR relaxometry was performed to determine the spin-lattice (T1) and spin-spin (T2) relaxation times. A decrease in T2 of the PEO segment in both l-MOM and c-MO was observed above Tc, suggesting that slow large-scale motions, such as the detachment of a chain end from the core, bridging, and interpenetration of the micelles, were inhibited. T1 of the PEO segment in l-MOM continuously increased in the experimental temperature range, indicating that the segment is hydrated even above its Tc. On the other hand, that of c-MO reached a ceiling above its Tc, likely due to the prevention of the rotation of the PEO main chain bonds caused by dehydration. Similar results were obtained for linear (ethyl acrylate)8(ethylene oxide)79(ethyl acrylate)8 (Mn = 800-3500-800, l-EOE) and its cyclic (ethyl acrylate)15(ethylene oxide)78 (Mn = 1500-3400, c-EO).

Double conformational transition of alkali metal poly(L-glutamate)s in aqueous ethanol: counterion mixing effect revisited.

It was first found that alkali metal poly(L-glutamate)s show the coil-globule transition and the coil-helix transition sequentially in aqueous ethanol with increasing the solvent concentration. The counterion specificity for the former transition, i.e., Na(+)>K(+), Rb(+)>Li(+), Cs(+), proved to be somewhat different from that for the latter; Na(+)>Li(+)>K(+)>Rb(+)>Cs(+). Counterion mixing effects were also observed for both transitions; the most effective combinations to induce the transitions were Li(+)/Cs(+) and Li(+)/K(+), respectively. Solution viscometry, circular dichroism and alkali metal NMR line width measurements for the single-counterion systems revealed that the contact ion-pair formation hardly occurs for Li(+) even at the collapsed globule state and in the helix conformation. Unexpectedly, however, the specific binding of Li(+) was induced just by mixing with K(+) or Cs(+), when the helix content concomitantly increased. Mechanism for the counterion-specific "double transition" as well as the counterion mixing effect is discussed referring to the size-fitting model that has been proposed for the coil-globule transition of alkali metal poly(acrylate)s.

Pt-free cathode catalysts prepared via multi-step pyrolysis of Fe phthalocyanine and phenolic resin for fuel cells.

Pt-free cathode catalysts for polymer electrolyte membrane fuel cells have been prepared by multi-step pyrolysis of FePc and PhRs, in the best of which show extensively high initial cell performance and good durability compared to other present precious-metal-free cathode catalysts to date.

Dynamic transport in Li-conductive polymer electrolytes plasticized with poly(ethylene glycol)-borate/aluminate ester.

The addition of plasticizers into Li(+)-conductive solid polymer electrolytes (SPEs) is a commonly known technique to enhance the ionic conductivity. Among the used plasticizers, alkoxides of group-13 elements [such as poly(ethylene glycol) (PEG)-borate ester] are promising candidates due to the Lewis acidity of the elements of this group (i.e. B, Al, and so on), which interact with the anions and may increase the degree of dissociation of the salts and the transport number of the SPEs. By means of pulsed-gradient stimulated-echo NMR (PGStE-NMR) and AC impedance measurements, we investigate the effect of Lewis acidity originated from group-13 elements on the transport number and the dissociation rate of SPEs containing various plasticizers. Our results show that the degree of salt dissociation is significantly enhanced by the addition of plasticizers including group-13 elements, whereas only a small or negligible increase of the transport number is observed for these SPEs. We infer that the plasticizers exhibiting Lewis acidity associate with the anions, and that the associated pairs can migrate in the SPEs as fast as free anions, which results in a lower transport number than expected.

Water properties in the super-salt-resistive gel probed by NMR and DSC.

The so-called "super-salt-resistive gel", or poly(4-vinylphenol) (P4VPh) hydrogel, of different water contents ( H = 97-51%) was prepared by cross-linking with different amounts of ethylene glycol diglycidyl ether. 1H NMR spectroscopy was used to investigate the dynamic properties of water in the gel samples in terms of the spin-spin relaxation. The T2 values in those hydrogels were analyzed by assuming a two-component system, namely, T 2(long) and T2(short), and their fractions were obtained. In the higher water content region (75% < or = H < or = 97%), T2(long) for P4VPh gel was almost constant or even slightly increased with decreasing temperature. On the other hand, T2(long) for poly(vinyl alcohol) (PVA) gel (80% < or = H < or = 96%) significantly decreased with decreasing temperature, showing a natural behavior for water mobility in common hydrogels. Water in P4VPh gels of lower water contents ( H = 70% and 51%) also showed intriguing behaviors: the T2 values are much larger than those of gels with higher water contents and decreased with decreasing temperature only in the lower temperature range (<10 degrees C). The fraction of T2(long) values of P4VPh gel showed another contrast to those of PVA gel; the latter decreased with decreasing water content (normal behavior), while in the former gel the highest fraction (ca. 60% at 20 degrees C) was observed for a sample with the lowest water content ( H = 51%). On the other hand, the results of DSC measurements for P4VPh gel were less specific than those of T2 and comparable to those of common hydrogels such as PVA; with decreasing water content, the total amounts of free water and freezable bound water per polymer mass (g/g) decreased, while the amount of nonfreezing water per polymer also decreased.

Diffusional behavior of poly(beta-benzyl L-aspartate) in the rodlike, random-coil, and intermediate forms as studied by high field-gradient 1H NMR spectroscopy.

The diffusion coefficients of poly(beta-benzyl L-aspartate)(PBLA) with the alpha-helix (rodlike) form in chloroform and the random-coil form in a mixture of chloroform and trifluoroacetic acid have been measured as a function of the PBLA concentration (C(PBLA)) by using high field-gradient 1H NMR. The PBLA concentration range for the former is from 0.11 to 9.20 wt % and for the latter it is from 0.20 to 25.2 wt %. From these experimental results, it is found that the diffusion coefficient of PBLA in the rodlike form is much smaller than that of PBLA in the random-coil form at the same PBLA concentration. This implies that the small diffusion coefficients of PBLA in the rodlike form as compared with those in the random-coil form come from the relatively large radius of gyration Rg. Further, it is found that the diffusional behavior of PBLA in the rodlike form is different in the three PBLA concentration regions, that is, region 1 (C(PBLA) = 0.11 approximately 0.39 wt %), region 2 (C(PBLA) = 0.39 approximately 0.86 wt %), and region 3 (C(PBLA) = 0.86 approximately 9.20 wt %). In the random-coil form, the diffusion is different in the two PBLA concentration regions, that is, region I (C(PBLA) = 0.20 approximately 1.03 wt %) and region II (C(PBLA) = 1.03 approximately 25.2 wt %). These diffusional behaviors in the rodlike form and in the random-coil form can be reasonably explained by Tinland-Maret-Rinaudo theory and de Gennes theory, respectively. Further, transitional change from the rodlike form to the random-coil form is discussed on the basis of the diffusional behavior.

Structural characterization of poly(diethylsiloxane) in the crystalline, liquid crystalline and isotropic phases by solid-state 17O NMR spectroscopy and ab initio MO calculations.

The structure of poly(diethylsiloxane) (PDES) has been characterized using solid-state NMR of (17)O. The sample studied had a weight-average molecular weight of 2.45 x 10(5). The sample was prepared by utilizing the cationic ring-opening polymerization of (17)O-enriched hexacyclotrisiloxane. Solid-state NMR of (17)O-enriched PDES was measured on the low-temperature beta(1) phase, the high-temperature beta(2) phase, the two-phase system consisting of the liquid crystal and isotropic liquid phase and the isotropic phase. From these data, the molecular structure and dynamics of PDES in the various phases were characterized via the chemical shifts of (17)O, and electric field gradient parameters were determined from NMR and ab initio molecular orbital (MO) calculations. In addition to the solid-state NMR of (1)H, (13)C and (29)Si previously reported on these samples, knowledge of the dynamic behavior of PDES as inferred from the NMR of (17)O in the present study was enhanced significantly. Further, the potential of combining the experimental NMR of (17)O with ab initio MO calculations to characterize the dynamics of polymers containing oxygen is demonstrated.

Oxidative polymerization of 1,4-diethynylbenzene into highly conjugated poly(phenylene butadiynylene) within the channels of surface-functionalized mesoporous silica and alumina materials.

A polyalkynylene-based conducting polymer (molecular wire) has been synthesized within the Cu-functionalized mesoporous MCM-41 silica catalyst. Fluorescence and 13C solid-state NMR provided spectroscopic evidence that the synthesis of extended polymeric chains with a high degree of alignment requires homogeneously distributed catalytic sites throughout the entire MCM matrix. This type of homogeneity has been achieved via co-condensation of the catalytic groups in narrow pores. In addition, our results indicated that proper adjustment of the pore diameter is vital to prevent clogging of the pores with aggregated or cross-linked polymers or both.

A study of conformational stability of poly(L-alanine), poly(L-valine), and poly(L-alanine)/poly(L-valine) blends in the solid state by (13)C cross-polarization/magic angle spinning NMR.

13C cross-polarization/magic angle spinning (CP/MAS) NMR and (1)H T(1rho) experiments of poly(L-alanine) (PLA), poly(L-valine) (PLV), and PLA/PLV blends have been carried out in order to elucidate the conformational stability of the polypeptides in the solid state. These were prepared by adding a trifluoroacetic acid (TFA) solution of the polymer with a 2.0 wt/wt % of sulfuric acid (H(2)SO(4)) to alkaline water. From these experimental results, it is clarified that the conformations of PLA and PLV in their blends are strongly influenced by intermolecular hydrogen-bonding interactions that cause their miscibility at the molecular level.