Ultimate tensile behavior of linear polyethylene solids

The influence of the elongation rate and temperature on the ultimate tensile properties of melt‐crystallized linear polyethylene solids was investigated, with a double‐edge‐notched specimen to avoid necking, in which uniform deformation could be assumed throughout the experiment. The data on ultimate properties such as the tensile strength and elongation at break for different temperatures could be superimposed, by shifts along the elongation rate axis, to give a master curve as a function of the time to rupture. The shift factors obtained from the superpositioning of both the tensile strength and ultimate strain took the form of the Williams–Landel–Ferry equation. As a result, the ultimate data provided a failure envelope curve that made it possible to predict rupture times when the tensile tests were conducted under any experimental conditions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2018–2026, 2002     

Bisphenol A-recognition polymers prepared by covalent molecular imprinting

A specific recognition material for bisphenol A (BPA) was prepared by using a covalent imprinting technique. A chloroform solution containing bisphenol A dimethacrylate as a template, ethylene glycol dimethacrylate as a cross-linking agent and 2,2′-azobis(isobutyronitrile) as an initiator was polymerized by UV initiation. When BPA was removed from the resulting polymer by hydrolysis of the ester bonds with aqueous sodium hydroxide, carboxylic acid residues were generated in the polymer. After the polymer was packed into a stainless steel column, retention factors of BPA and related compounds were measured. The imprinted polymer adsorbed BPA and structurally related compounds such as 4,4′-dihydroxybenzophenone, bis(4-hydroxyphenyl)sulfone and 4,4′-dihydroxybiphenyl. A typical association constant (K_a) was calculated to be 1.72×10⁵ M⁻¹ by Scatchard analysis. Interestingly, 17α- and 17β-estradiol were also bound to the imprinted polymer (K_a=1.68×10⁵ M⁻¹), indicating that the polymer could be used as artificial receptors for screening the compounds having estrogenic action.     

On-line concentration of a protein using denaturation by sodium dodecyl sulfate.

A novel method for the on-column sample stacking of proteins is described. The strategy takes advantage of interactions between protein molecules and sodium dodecyl sulfate (SDS) monomers. A long plug of a protein sample (either acidic or basic) is injected into a capillary filled with a background electrolyte (BGE) containing SDS. When a potential is applied, the proteins interact with SDS monomers in the BGE to form protein-SDS complexes that migrate more slowly than the corresponding uncomplexed protein, resulting in protein stacking. Both acidic and basic proteins migrate at an almost identical electrophoretic velocity after stacking, which indicates that the protein-SDS complexes formed in the BGE zone have a similar charge/mass ratio. The mechanism of stacking was investigated using a sample consisting of a basic protein, lysozyme, and a small molecule, methylene blue. The findings clearly show that two interactions with SDS occur, a stepwise binding interaction between protein molecules and SDS monomers and an interaction in which the small molecules enter into micelles formed by SDS molecules. The method was also applied to the detection of a protein labeled with a fluorescent labeling reagent at trace levels. The labeled protein was detected even under labeling conditions where the labeling efficiency was too low to detect by short-plug injection.     

Speciation of chromium in seawater by ICP-AES with dual mini-columns containing chelating resin.

A method for the preconcentration and speciation of chromium in seawater was developed. On-line preconcentration and determination were carried out by using inductively coupled plasma atomic emission spectrometry (ICP-AES) with dual mini-columns containing a chelating resin. In this system, Cr(III) was collected on the first column. The effluent containing residual chromium from the first column was collected on the second column after passing through a reduction-switching unit, in which the reducing agent was introduced, or not, for the reduction of Cr(VI) to Cr(lII). Cr(VI) was determined as the difference between the concentration of pre-reduced Cr(VI) and Cr(III) in the effluent from the first column. The detection limits for Cr(III) and Cr(VI) were 0.04 and 0.09 microg l(-1), respectively.     

Synthesis of well‐defined polymers end‐functionalized with crosslinkable aziridine groups by living anionic polymerization

Well‐defined end‐functionalized polystyrene, poly(α‐methylstyrene), and polyisoprene with polymerizable aziridine groups were synthesized by the termination reactions of the anionic living polymers of styrene, α‐methylstyrene, and isoprene with 1‐[2‐(4‐chlorobutoxy)ethyl]aziridine in tetrahydrofuran at ?78 °C. The resulting polymers possessed the predicted molecular weights and narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.1) as well as aziridine terminal moieties. The cationic ring‐opening polymerization of the ω‐monofunctionalized polystyrene having an aziridinyl group with Et₃OBF₄ gave the polymacromonomer, whereas the α,ω‐difunctional polystyrene underwent crosslinking reactions to afford an insoluble gel. Crosslinking products were similarly obtained by the reaction of the α,ω‐diaziridinyl polystyrene with poly(acrylic acid)‐co‐poly(butyl acrylate). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4126–4135, 2005     

Estimate of the difference between the Kac operator and the Schrödinger semigroup

An operator norm estimate of the difference between the Kac operator and the Schrödinger semigroup is proved and used to give a variant of the Trotter product formula for Schrödinger operators in theL ^p operator norm. This extends Helffer’s result in theL ² operator norm to the case in theL ^p operator norm for more general scalar potentials and with vector potentials. The method of the proof is probabilistic based on the Feynman—Kac and Feynman—Kac—Itô formula.     

Fluorescence resonance energy transfer by quencher adsorption into hydrogels containing fluorophores

We synthesized anionic hydrogels containing fluorophores and investigated the adsorption of a cationic quencher having an amino group into hydrogels by fluorescence resonance energy transfer (FRET). FRET from the fluorophore to the quencher in hydrogels was examined by fluorescence intensity and fluorescence decay using a fluorescence spectrophotometer and femtosecond laser spectroscopy. The fluorescence intensity of the fluorophore‐containing hydrogels decreased rapidly with increasing amounts of adsorbed cationic quencher. The fluorescence emission of the fluorophore in the quencher‐adsorbed hydrogels containing fluorophores decayed more rapidly than that of the original hydrogels. The aforementioned result indicates that the fluorescence of the fluorophore‐containing hydrogels is quenched due to FRET from the fluorophore to the quencher as the cationic quenchers can approach the fluorophores in hydrogels by electrostatic interactions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3245–3252, 2006     

Synthesis and electrochemical and electroluminescent properties of N‐phenylcarbazole‐substituted poly(p‐phenylenevinylene)

An N‐phenylcarbazole‐containing poly(p‐phenylenevinylene) (PPV), poly[(2‐(4′‐carbazol‐9‐yl‐phenyl)‐5‐octyloxy‐1,4‐phenylenevinylene)‐alt‐(2‐(2′‐ethylhexyloxy)‐5‐methoxy‐1,4‐phenylenevinylene)] (Cz‐PPV), was synthesized, and its optical, electrochemical, and electroluminescent properties were studied. The molecular structures of the key intermediates, the carbazole‐containing boronic ester and the dialdehyde monomer, were crystallographically characterized. The polymer was soluble in common organic solvents and exhibited good thermal stability with a 5% weight loss at temperatures above 420 °C in nitrogen. A cyclic voltammogram showed the oxidation peak potentials of both the pendant carbazole group and the PPV main chain, indicating that the hole‐injection ability of the polymer would be improved by the introduction of the carbazole‐functional group. A single‐layer light‐emitting diode (LED) with a simple configuration of indium tin oxide (ITO)/Cz‐PPV (80 nm)/Ca/Al exhibited a bright yellow emission with a brightness of 1560 cd/m² at a bias of 11 V and a current density of 565 mA/cm². A double‐layer LED device with the configuration of ITO/poly(3,4‐ethylenedioxy‐2,5‐thiophene):poly (styrenesulfonic acid) (60 nm)/Cz‐PPV (80 nm)/Ca/Al gave a low turn‐on voltage at 3 V and a maximum brightness of 6600 cd/m² at a bias of 8 V. The maximum electroluminescent efficiency corresponding to the double‐layer device was 1.15 cd/A, 0.42 lm/W, and 0.5%. The desired electroluminescence results demonstrated that the incorporation of hole‐transporting functional groups into the PPVs was effective for enhancing the electroluminescent performance. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5765–5773, 2005     

Synthesis and properties of π‐conjugated dithiafulvene oligomers by addition of a monofunctionalized compound

Dithiafulvene oligomers ( 3 ) were prepared by cycloaddition polymerization of aldothioketenes with their alkynethiol tautomers derived from 1,4‐diethynylbenzene ( 2 ) with the addition of 1‐ethynyl‐4‐methylbenzene ( 1 ) as a monofunctionalized compound. Different feed ratios of 2 / 1 were used to control the molecular weights of 3 . The structures of 3 were confirmed by IR and ¹H NMR spectroscopies in comparison with those of 2‐(4‐tolylidene)‐4‐tolyl‐1,3‐dithiol ( 4 ) as a model compound, which was obtained by the treatment of lithium 2‐tolylethynethiolate with water in Et₂O. The number‐average degree of polymerization (DP) and the number‐average molecular weight were measured by gel permeation chromatographic and ¹H NMR analysis. DP increased with an increasing feed ratio of 2 / 1 . The ultraviolet–visible spectra of 3 in diluted acetonitrile showed that the absorption maxima of 3 increased with an increasing DP of 3 . These redshifts are ascribed to an effective expansion of the π‐conjugation system in 3 . The oligomers exhibited a maximum conjugation length of seven repeating units. The redox properties of 3 were examined by cyclic voltammetry. The oxidation half‐peak potentials (E_p/2) of 3 were slightly cathodically shifted with increasing DP. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 708–715, 2003     

Classification of non‐well‐founded sets and an application

A complete list of Finsler, Scott and Boffa sets whose transitive closures contain 1, 2 and 3 elements is given. An algorithm for deciding the identity of hereditarily finite Scott sets is presented. Anti‐well‐founded (awf) sets, i. e., non‐well‐founded sets whose all maximal ∈‐paths are circular, are studied. For example they form transitive inner models of ZFC minus foundation and empty set, and they include uncountably many hereditarily finite awf sets. A complete list of Finsler and Boffa awf sets with 2 and 3 elements in their transitive closure is given. Next the existence of infinite descending ∈‐sequences in Aczel universes is shown. Finally a theorem of Ballard and Hrbá?ek concerning nonstandard Boffa universes of sets is considerably extended.