Free‐radical copolymerization of vinyl esters using fluoroalcohols as solvents: The solvent effect on the monomer reactivity ratio

Free‐radical copolymerizations of vinyl acetate (VAc = M₁) and other vinyl esters (= M₂) including vinyl pivalate (VPi), vinyl 2,2‐bis(trifluoromethyl)propionate (VF6Pi), and vinyl benzoate (VBz) with fluoroalcohols and tetrahydrofuran (THF) as the solvents were investigated. The fluoroalcohols affected not only the stereochemistry but also the polymerization rate. The polymerization rate was higher in the fluoroalcohols than in THF. The accelerating effect of the fluoroalcohols on the polymerization was probably due to the interaction of the solvents with the ester side groups of the monomers and growing radical species. The difference in the monomer reactivity ratios (r₁, r₂) in THF and 2,2,2‐trifluoroethanol was relatively small for all reaction conditions and for the monomers tested in this work, whereas r₁ increased in the VAc‐VF6Pi copolymerization and r₂ decreased in the VAc‐VPi copolymerization when perfluoro‐tert‐butyl alcohol was used as the solvent. These results were ascribed to steric and monomer‐activating effects due to the hydrogen bonding between the monomers and solvents. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 220–228, 2000     

Stereocontrol in the free‐radical polymerization of methacrylates with fluoroalcohols

The free‐radical polymerization of methyl methacrylate (MMA), ethyl methacrylate (EMA), isopropyl methacrylate (IPMA), and tert‐butyl methacrylate (t‐BuMA) was carried out under various conditions to achieve stereoregulation. In the MMA polymerization, syndiotactic specificity was enhanced by the use of fluoroalcohols, including (CF₃)₃COH as a solvent or an additive. The polymerization of MMA in (CF₃)₃COH at −98 °C achieved the highest syndiotacticity (rr = 93%) for the radical polymerization of methacrylates. Similar effects of fluoroalcohols enhancing syndiotactic specificity were also observed in the polymerization of EMA, whereas the effect was negligible in the IPMA polymerization. In contrast to the polymerizations of MMA and EMA, syndiotactic specificity was decreased by the use of (CF₃)₃COH in the t‐BuMA polymerization. The stereoeffects of fluoroalcohols seemed to be due to the hydrogen‐bonding interaction of the alcohols with monomers and growing species. The interaction was confirmed by NMR measurements. In addition, in the bulk polymerization of MMA at −78 °C, syndiotactic specificity and polymer yield increased even in the presence of a small amount {[(CF₃)₃COH]/[MMA]_o < 1} of (CF₃)₃COH. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4693–4703, 2000     

Image enhancement with lightness correction and image sharpening based on characteristics of vision for elderly persons

Optical Review - In general, as people age the functions of their sensory organs deteriorate. For example, in the eye of an elderly person, the visual field becomes dark owing to a decrease in the...     

Lewis acid-promoted cyclization of heteroatom-substituted enynes

Lewis acid-promoted cyclizations of heteroatom-substituted enynes have been examined. The reaction of enynes and bearing silicon substituents on an alkyne afforded the halogenated five-membered gamma-lactones and gamma-lactams as the main products. The reaction of substrates and having 2-phosphonoacrylate instead of malonate also gave halogenated five-membered cyclic compounds and as the major products. The cyclized products are highly substituted and potentially useful for further synthetic transformations.     

Characterization of dissolved organic matter released from Microcystis aeruginosa.

The contribution of dissolved organic matter (DOM) released from phytoplankton (Microcystis aeruginosa) during cultivation and biodegradation was examined to clarify the causes of the organic pollution of Lake Biwa. Two peaks, peak 2 (retention time (RT) = 32 min) and peak 3 (RT = 35 min), were detected in the algal DOM released from Microcystis aeruginosa during cultivation and biodegradation by gel chromatography with a fluorescence detector (Ex = 340 nm, Em = 435 nm). As these peaks correspond with the peaks detected in the surface water of Lake Biwa, one can conclude that the algal DOM released from Microcystis aeruginosa during cultivation and biodegradation makes a considerable contribution to the refractory organic matter in Lake Biwa. Three fluorescence maxima were observed in the cultivation of Microcystis aeruginosa: a fulvic-like fluorescence peak (peak A) with Ex/Em values of 320/430 nm, a protein-like fluorescence peak (peak C) with Ex/Em values of 280/360 nm, and another peak with Ex/Em values of 240/370 nm. The fluorescence material of peak C has a larger MW than that of peak A. The algal-derived DOM from Microcystis aeruginosa has similar fluorescence to fulvic acid of soil origin but exhibits mainly hydrophilic characteristics. In the biodegradation of Microcystis aeruginosa, a fulvic-like fluorescence peak (peak B) with Ex/Em values of 250/440 nm and a peak with Ex/Em values of 320/380 nm were observed.     

Effect of ketimide ligand for ethylene polymerization and ethylene/norbornene copolymerization catalyzed by (cyclopentadienyl)(ketimide)titanium complexes-MAO catalyst systems: Structural analysis for CpTiCl2(NCPh2)

Ligand effects on the catalytic activity [and norbornene (NBE) incorporation] for both ethylene polymerization and ethylene/NBE copolymerization using half-titanocenes (titanium half-sandwich complexes) containing ketimide ligand of type Cp′TiCl₂[NC(R¹)R²] [Cp′ = Cp (1), C⁵Me⁵ (Cp^∗, 2); R¹,R² = ^tBu,^tBu (a), ^tBu,Ph (b), Ph,Ph (c)]-methylaluminoxane (MAO) catalyst systems have been investigated. CpTiCl₂[NC(^tBu)Ph] (1b) CpTiCl₂(NCPh₂) (1c), and Cp^∗TiCl₂(NCPh₂) (2c) were prepared and identified; the structure of Cp^∗TiCl₂(NCPh₂) (2c) was determined by X-ray crystallography. The catalytic activity for ethylene polymerization increased in the order: 1a > 1b > 1c, suggesting that an electronic nature of the ketimide ligand affects the activity. However, molecular weight distributions for resultant (co)polymers prepared by 1b,c and by 2c-MAO catalyst systems were bi- or multi-modal, suggesting that the ketimide substituent plays a key role in order for these (co)polymerizations to proceed with single catalytically-active species. CpTiCl₂(NC^tBu₂) (1a) exhibited both remarkable catalytic activity and efficient NBE incorporation for ethylene/NBE copolymerization.     

Electrical conductivity of π-conjugated polymers with nitro substituents

π-Conjugated polymers bearing nitro substituent(s), e.g., poly(aryleneethynylene) (PAE) type polymers and poly(4,8-dinitroanthraquinone-1,5-diyl) P(4,8-NO₂-1,5-AQ), show semiconducting properties with electrical conductivities of an order of 10⁻⁷ to 10⁻⁶ S · cm⁻¹ at room temperature without special oxidation and reduction of the polymer. P(4,8-NO₂-1,5-AQ) shows a large shift of phase in alternating current (ac) measurements and a unique magnetism at low temperature.     

End‐functionalization of polystyrene by malto‐oligosaccharide generating aggregation‐tunable polymeric reverse micelle

This article describes that glucose, maltose, maltotriose, maltotetraose, maltopentaose, and maltohexaose ( a , b , c , d , e , and f , respectively) were introduced into the initiating chain‐end of polystyrene (PSt) through the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO)‐mediated radical polymerization. A series of glycoconjuaged TEMPO‐adducts, 1a–f , was synthesized and used as the initiators for the polymerization of styrene (St) for 6 h at 120 °C to afford the end‐functionalized PSt's with the acetyl saccharides, 2a–f , in the yields of 37–43%. For 2a–f obtained by the polymerizations using the [St]/[ 1 ] of 125, 250, and 500, the number‐average molecular weights determined by size exclusion chromatography (SEC), M_n,SEC's, were 4800–6300, 8800–10,600, and 18,400–25,200, respectively, which fairly agreed with the predicted values. The end‐functionalized PSt's with saccharides, 3a–f , which were obtained from the deacetylation of 2a–f using sodium methoxide in dry THF, formed the polymeric reverse micelles consisting of a saccharide‐core and a PSt‐shell in chloroform and toluene. The static laser light scattering (SLS) measurements provided the average molar mass of the aggregates in toluene, M_w,SLS's, which ranged from 7.50 × 10⁴ to 1.77 × 10⁵ for 3a , from 1.90 × 10⁵ to 4.93 × 10⁵ for 3b , from 4.41 × 10⁵ to 7.21 × 10⁵ for 3c , from 5.85 × 10⁵ to 8.51 × 10⁵ for 3d , from 7.55 × 10⁵ to 8.53 × 10⁵ for 3e , and from 8.54 × 10⁵ to 9.26 × 10⁵ for 3f . The aggregation numbers, N_agg's, which were calculated from the M_w,SLS's, were from 7 to 24 for 3a , from 20 to 37 for 3b , from 34 to 89 for 3c , from 39 to 116 for 3d , from 41 to 145 for 3e , and from 31 to 146 for 3f . It was confirmed that the aggregation property, such as the M_w,SLS or N_agg values, was strongly related to the polymerization degrees of St (DP's) or the number of the glucose residues (n's) for 3a–f . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4864–4879, 2006     

Preparation and porous control of amorphous carbons by co-defluorination of perfluorooctane and octafluorotoluene in vapor phases at 423 K

Two types of perfluorocarbon compounds, aliphatic perfluorooctane and aromatic octafluorotoluene, were co-defluorinated using sodium metal, and amorphous carbons were deposited from the vapor phase at very low temperature, 423 K. The products showed morphologies composed of fibrous, platelet, and spherical forms, which were dependent on the mixing ratio of the two. The BET surface areas also correlated well with the ratio of the starting mixtures, indicating that the surface area could be adjusted by changing the mixing ratio of these two compounds. However, when the carbonaceous product was further annealed in situ at 573 or 673 K, the porosities also modified. First the porosity decreased at 573 K, then increased greatly at 673 K, where radical interaction to shrink the pores and crystal growth of template fluoride occurred at 573 K and 673 K, respectively.