Structural development of ultra‐high strength polyethylene fibers: Transformation from kebabs to shishs through hot‐drawing process of gel‐spun fibers

Structural development of ultra‐high strength polyethylene fibers via hot‐drawing processes of as‐spun gel fibers was investigated by means of transmission electron microscopy. It is found that the shish‐kebabs developed in both the as‐spun and drawn fibers can be transformed continuously into the micro‐fibril structure composed mostly of the shish structure through the hot‐drawing process. The structure transformation involves a drastic decrease in diameter of the kebab plus the shish but almost no change in the shish diameter. This result suggests that the chains in the kebabs are incorporated into the shishs and consumed to extend the longitudinal dimension of the shishs during the drawing process. The proposed new deformation model well explains the relationship between the fiber morphology and their mechanical properties: the tensile strength and modulus of the fibers can be determined by the number of the shish in the fiber and the macroscopic diameter of the fiber, which are apriori determined at the spinning process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1861–1872, 2010     

Anionic polymerization of N,N‐dialkyl‐2‐methylenebut‐3‐enamide: Effect of alkyl substituents on polymerization behavior

Anionic polymerizations of three 1,3‐butadiene derivatives containing different N,N‐dialkyl amide functions, N,N‐diisopropylamide (DiPA), piperidineamide (PiA), and cis‐2,6‐dimethylpiperidineamide (DMPA) were performed under various conditions, and their polymerization behavior was compared with that of N,N‐diethylamide analogue (DEA), which was previously reported. When polymerization of DiPA was performed at ?78 °C with potassium counter ion, only trace amounts of oligomers were formed, whereas polymers with a narrow molecular weight distribution were obtained in moderate yield when DiPA was polymerized at 0 °C in the presence of LiCl. Decrease in molecular weight and broadening of molecular weight distribution were observed when polymerization was performed at a higher temperature of 20 °C, presumably because of the effect of ceiling temperature. In the case of DMPA, no polymer was formed at 0 °C and polymers with relatively broad molecular weight distributions (M_w/M_n = 1.2) were obtained at 20 °C. The polymerization rate of PiA was much faster than that of the other monomers, and poly(PiA) was obtained in high yield even at ?78 °C in 24 h. The microstructure of the resulting polymers were exclusively 1,4‐ for poly(DMPA), whereas 20–30% of the 1,2‐structure was contained in poly(DiPA) and poly(PiA). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3714–3721, 2010     

Oxygen‐sensing properties of 5,10,15,20‐tetraphenylporphinato platinum(II) and palladium(II) covalently bound on poly(isobutyl‐co‐2,2,2‐trifluoroethyl methacrylate)

A novel methacrylate monomer bearing 5,10,15,20‐tetraphenylporphyrinato palladium(II) (PdTPP) (monomer 1a ) was synthesized and copolymerized with isobutyl methacrylate (IBM) and 2,2,2‐trifluoroethyl methacrylate (TFEM) to give poly (IBM‐co‐TFEM) bearing PdTPP (copolymer 2a ) as a dye‐conjugated oxygen‐permeable polymer for pressure‐sensitive paint applications. The introduction of PdTPP into copolymer 2a was confirmed by UV–vis spectroscopy and extended X‐ray absorption fine structure analysis. The Stern–Volmer plots of the copolymer 2a and a mixture of PdTPP and poly(IBM‐co‐TFEM) both showed downward curvature, unlike that of the platinum complex analogue (copolymer 2b ) previously reported. The plots were successfully fitted with a two‐site model to give two distinct Stern–Volmer constants (K_SV1 and K_SV2) and the partition ratio f₁. Interestingly, the f₁ values for the copolymer 2a were almost constant at about 0.98, whereas those of the mixture of PdTPP and poly(IBM‐co‐TFEM) increased from 0.889 to 0.967 as the temperature was increased. This finding suggests that there are two distinct microheterogeneities, one temperature‐dependent and the other temperature‐independent, in the mixture of PdTPP and poly(IBM‐co‐TFEM). The dye‐conjugation approach effectively eliminates the temperature‐dependent, but not the temperature‐independent microheterogeneity. The luminescence decays of copolymers 2a and 2b and the corresponding mixtures in the absence of oxygen indicated that the temperature‐dependent microheterogeneity involves an oxygen diffusion process, whereas the temperature‐independent one appears to be inherent nature in PdTPP. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 663–670, 2010     

Ionic polymers and oligomers with expanded π-conjugation system derived from through-space interaction in piperazinium ring

Reactions of N-(2,4-dinitrophenyl)-4-arylpyridinium chlorides (aryl (Ar) = phenyl and 4-pyridyl) with piperazines caused the ring opening of the pyridinium ring and yielded polymers that consisted of 5-piperazinium-3-aryl-penta-2,4-dienylideneammonium chloride units [N(CH(R)CH₂)₂N⁺(Cl⁻)CHCHC(Ar)CHCH, RH, Me, and phenyl]. However, the same reactions occurring in the presence of piperidine yielded oligomers that consisted of 5-piperazinium-3-aryl-penta-2,4-dienylideneammonium chloride units having piperidine and/or piperazine rings at both ends. ¹H NMR spectra suggested that π-electrons of the penta-2,4-dienylideneammonium group of the polymers and the oligomers were delocalized. UV-vis measurements revealed that the π-conjugation system expanded along the polymer and oligomer chains due to the orbital interaction between electrons on the two nitrogen atoms of the piperazinium ring. Conversion of the piperazinium ring from the boat form to the chair form caused decrease in the π-conjugation length. The rate constants of the conversion of the oligomers depended on their chain lengths. The surface of pellets that were molded from the polymers and oligomers exhibited metallic luster. These polymers and oligomers underwent electrochemical oxidation in solution.     

Density functional theory investigation of novel Eu(III) complexes with asymmetric bis(phosphine) oxides

Recently, we have developed novel Eu(III) complexes with three beta-diketonates and one asymmetric bis(phosphine) oxide whose light emission intensity is drastically increased. In this paper, one of these complexes is investigated by the density functional theory calculation. Sixteen isomers of this complex have been considered. The ratio of the existence for the most stable isomer (B1_1a) is found to be about 51%, and the sum of the ratio of the existence for the six most stable isomers (B1_1a, B1_3a, B1_8a, B1_2a, B1_1b, and B1_5a) is about 100%, assuming the Boltzmann distribution (T = 300 K). The coordination structures of the six most stable isomers in the ground states are similar, and we can expect asymmetric ligand fields for them, favorable for the efficient light emission. Vertical excitation energies and oscillator strengths for each isomer have been obtained by the time-dependent density functional theory. With the red-shift of the wavelength and the interpolation by Gaussian convolution, both the calculated absorption spectra for the most stable isomer B1_1a and the calculated absorption spectra for the ensemble average of the isomers are found to be similar to the experimental fluorescence excitation spectra. The efficiency of energy transfer from the triplet excited state to the Eu(III) ion is considered by calculating DeltaEET (difference between the adiabatic excitation energy of the complex for the lowest triplet state and the emission energy of the Eu(III) ion for 5D0 to 7F2). The characters for the lowest triplet states for the isomers are investigated by the spin density distributions of the triplet states.     

Lipase-catalyzed synthesis and curing of high-molecular-weight polyricinoleate

High-molecular-weight polyricinoleate, with an M(w) of 100,600, was enzymatically prepared by the polycondensation of methylricinoleate using immobilized lipase from Pseudomonas cepacia (IM-PC) in bulk in the presence of 4 A molecular sieves at 80 degrees C for 7 d. Polyricinoleate was a viscous liquid at room temperature with a glass transition temperature (T(g)) of -74.8 degrees C, showed no crystallinity and was biodegraded by activated sludge. Polyricinoleate was readily cured using a dicumyl peroxide at 170 degrees C for 30 min to produce a chloroform insoluble crosslinked polyricinoleate with a hardness of 50A using durometer A.     

Self‐Assembled Fibers Containing Stable Organic Radical Moieties: Alignment and Magnetic Properties in Liquid Crystals

Macroscopically oriented stable organic radicals have been obtained by using a liquid–crystalline (LC) gel composed of an l ‐isoleucine‐based low molecular weight gelator containing a 2,2,6,6‐tetramethylpiperidine 1‐oxyl moiety. The LC gel has allowed magnetic measurements of the oriented organic radical. The gelator has formed fibrous aggregates in liquid crystals via intermolecular hydrogen bonds. The fibrous aggregates of the radical gelator are formed and oriented on cooling by applying a magnetic field to the mixture of liquid crystals and the gelator. Superconducting quantum interference device (SQUID) measurements have revealed that both oriented and nonoriented fibrous aggregates exhibited antiferromagnetic interactions, in which super‐exchange interaction constant J is estimated as ?0.89 cm^?1.     

Cross‐Coupling of Organolithium with Ethers or Aryl Ammonium Salts by C−O or C−N Bond Cleavage

Various aryl‐, alkenyl‐, and/or alkyllithium species reacted smoothly with aryl and/or benzyl ethers with cleavage of the inert C?O bond to afford cross‐coupled products, catalyzed by commercially available [Ni(cod)₂] (cod=1,5‐cyclooctadiene) catalysts with N‐heterocyclic carbene (NHC) ligands. Furthermore, the coupling reaction between the aryllithium compounds and aryl ammonium salts proceeded under mild conditions with C?N bond cleavage in the presence of a [Pd(PPh₃)₂Cl₂] catalyst. These methods enable selective sequential functionalizations of arenes having both C?N and C?O bonds in one pot.