Selective vinyl cationic polymerization of monomers with two cationically polymerizable groups. II. p-vinylphenyl glycidyl ether: An epoxy-functionalized styrene

p-Vinylphenyl glycidyl ether (VPGE), a styrene derivative with an epoxy pendant, was polymerized by various cationic initiators, and its selective vinyl polymerization was investigated at low temperatures below ?15°C. BF₃OEt₂ (a metal halide) and CF₃SO₃H (a strong protonic acid) polymerized both vinyl and epoxy groups of VPGE, and produced cross-linked insoluble polymers. The HI/I₂ initiating system and iodine, in contrast, polymerized its vinyl group in polar solvents (CH₂Cl₂ and nitroethane) highly selectively in the temperature range of ?15 to ?40°C to give soluble polymers with a polystyrene backbone and epoxy pendants; however, under these conditions, 10–15% of the epoxy groups of the polymers were consumed during the polymerization by the reaction with the growing species. The polymerization by HI/I₂ in CH₂CI₂ involved a long-lived propagating species, as indicated by a progressive increase in the molecular weight (M?_n) of the polymers with monomer conversion and their fairly narrow molecular weight distributions (M?_w/M?_n ～ 1.6). The differences between the polymerizations of VPGE and p-isopropenylphenyl glycidyl ether, an α-methylstyrene-type counterpart of VPGE, were also discussed with an emphasis on the effects of the α-methyl group in the latter monomer.     

Synthesis of pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxalines

Synthesis of pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxalines by the facile cyclizations of 2,3-dichloroquinoxalines with 2-aminopyridines and of 2-amino-3-chloroquinoxalines with various substituted pyridines is described.     

Small-angle neutron scattering study on microstructure of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) in water

By employing small-angle neutron scattering (SANS), we investigated the microstructures of, poly(N-isopropylacrylamide) (PNIPA)-block-poly(ethylene glycol) (PEG) (NE) in deuterated water D₂O, as related to macroscopic behaviors of fluidity, turbidity and synerisis. SANS revealed following results: (i) microphase separation occurs at around above 17 °C in a temperature range of transparent sol below 30 °C. In the microdomain appeared in the transparent sol state, both block chains of PNIPA and PEG are swollen by water; (ii) for the NE solution of polymer concentration W_p > 3.5% (w/v), corresponding to opaque gel above 30 °C, a percolated structure, i.e., network-like domain is formed by NE as a result of macrophase separation due to dehydration of the PNIPA chains. As the temperature increases toward 40 °C, the network domain is squeezed along a direction parallel to the NE interface, which leads to increase of the interfacial thickness given by swollen PEG chains and to the macroscopic synerisis behavior.     

Regioselectivity of Friedel-Crafts acylation of aromatic compounds with several cyclic anhydrides

The Friedel-Crafts acylations of various aromatic compounds with cyclic anhydrides such as 2-(p-substituted phenyl)butanedioic, 3-phenylpentanedioic and homophathlic anhydrides were carried out under various conditions in order to obtain informations about the regioselectivity of the ring opening of the cyclic anhydrides and about the possible reaction pathways in the acylations.     

Synthesis of new hydrolyzable polyurethanes from L‐gulonic acid‐derived diols and diisocyanates

New polyurethanes with lactone groups in the pendants and main chains were synthesized by the polyaddition of two kinds of L ‐gulonolactone‐derived diols (2,3‐O‐isopropylidene‐L ‐gulono‐1,4‐lactone and 5,6‐O‐isopropylidene‐L ‐gulono‐1,4‐lactone) with hexamethylene diisocyanate and methyl (S)‐2,6‐diisocyanatohexanoate and by the subsequent deprotection of isopropylidene groups. They were hydrolyzed more quickly than the polyurethane derived from methyl β‐D ‐glucofuranosidurono‐6,3‐lactone in a phosphate buffer solution, the pH value of which was 8.0, at 27 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4158–4166, 2002     

Thalidomide as a nitric oxide synthase inhibitor and its structural development

Thalidomide has been found to exhibit weak nitric oxide synthase (NOS)-inhibitory activity. Structural development studies of thalidomide showed that some N-2,6-dimethylphenylhomophthalimide analogs possess NOS-inhibiting activity.     

Electron beam treatment of lignite-burning flue gas with high concentrations of sulfur dioxide and water

Experiments were carried out to investigate the removals of SO₂ and NO_x from simulated lignite-burning flue gas containing SO₂ (4800 ppm), NO (320 ppm) and H₂O (22%) by electron beam irradiation. Removal efficiencies of SO₂ and NO_x were achieved to reach 97 and 88% at 70°C, and 74 and 85% at 80°C, respectively, with the dose of 10.3 kGy without NH₃ leakage. The higher removal efficiencies of SO₂ and NO_x were observed in simulated lignite-burning flue gas than in coal-fired flue gas containing 800 ppm of SO₂, 225 ppm of NO and 7.5% H₂O at the same treatment condition. The higher removal efficiencies were attributed to the higher concentrations of SO₂, H₂O, and added NH₃. Simulation calculations indicated that the higher concentrations of these components enhance the effective radical reactions to oxidize NO to form NO₂ with HO₂ radical, and to oxidize SO₂ to form SO₃ with OH radical and O₂. The reactions of NO_x with N and NH₂ radicals to produce N₂ and N₂O also promote the NO_x removal. By-product was determined to be the mixture of (NH₄)₂SO₄ and NH₄NO₃ containing a small amount of H₂SO₄.     

Length dependence of the optical transition energies of the exactly solvable Hubbard model for linear polyenes

Some accurate results on the length dependence of the excitation energies from the ground state to ionic excited states in the Hubbard model of linear polyenes are obtained based on the method of Lieb and Wu. To this end, it is first shown that singly ionic excited states with “plus” alternancy symmetry in the Hubbard model are described by the wave functions in which the two electron operator [∑(?)ⁿCC] is acted on (N ? 2)-electron covalent eigenstates. Then by solving the Lieb-Wu equations the exact excitation energies of the lowest ionic state, which corresponds to the E state in this model, are calculated for systems with up to 50 electrons. The result, together with a correction for the end effect, indicates that the excitation energies do not decrease as 1/N but converge to the limiting value more rapidly when the number of electrons N becomes large.     

Control of charge-transfer-induced spin transition temperature on cobalt-iron Prussian blue analogues

The electronic and spin states of a series of Co-Fe Prussian blue analogues containing Na(+) ion in the lattice, Na(x)()Co(y)()Fe(CN)(6) x zH(2)O, strongly depended on the atomic composition ratio of Co to Fe (Co/Fe) and temperature. Compounds of Co/Fe = 1.5 and 1.15 consisted mostly of the Fe(III)(t(2g)(5)e(g)(0), LS, S = 1/2)-CN-Co(II)(t(2g)(5)e(g)(2), HS, S = 3/2) site and the Fe(II)(t(2g)(6)e(g)(0), LS, S = 0)-CN-Co(III)(t(2g)(6)e(g)(0), LS, S = 0) site, respectively, over the entire temperature region from 5 to 350 K. Conversely, compounds of Co/Fe = 1.37, 1.32, and 1.26 showed a change in their electronic and spin states depending on the temperature. These compounds consisted mainly of the Fe(III)-CN-Co(II) site (HT phase) around room temperature but turned to the state consisting mainly of the Fe(II)-CN-Co(III) site (LT phase) at low temperatures. This charge-transfer-induced spin transition (CTIST) phenomenon occurred reversibly with a large thermal hysteresis of about 40 K. The CTIST temperature (T(1/2) = (T(1/2) descending + T(1/2) ascending)/2) increased from 200 to 280 K with decreasing Co/Fe from 1.37 to 1.26. Furthermore, by light illumination at 5 K, the LT phase of compounds of Co/Fe = 1.37, 1.32, and 1.26 was converted to the HT phase, and the relaxation temperature from this photoproduced HT phase also strongly depended on the Co/Fe ratio; 145 K for Co/Fe = 1.37, 125 K for Co/Fe = 1.32, and 110 K for Co/Fe = 1.26. All these phenomena are explained by a simple model using potential energy curves of the LT and HT phases. The energy difference of two phases is determined by the ligand field strength around Co(II) ions, which can be controlled by Co/Fe.