Synthesis and polyelectrolyte behavior of poly(methacrylic acid) star polymers

Poly(tert‐butyl methacrylate) [P(tBMA)] star polymers were synthesized by copolymerization of p(tBMA) macroinitiator with ethylene glycol dimethacrylate via atom transfer radical polymerization method. P(tBMA) stars had a narrow molecular weight distribution (M_w/M_n = 1.06–1.15). The ratio of radius of gyration to hydrodynamic radius R_G/R_H, which indicates inner segment density, was in the range 1.16–1.22 in tetrahydrofuran (THF) (arm number f = 25–142). These stars behaved not as hard spheres but as soft spheres in THF. Poly(methacrylic acid) stars were obtained by the hydrolysis of P(tBMA) arms. We investigated the conformation of star polyelectrolyte as a function of pH and ionic strength by means of dynamic light scattering (DLS). The hydrodynamic diameter increased gradually from 18.8 to 48.3 nm as a function of the solution pH. In addition, we compared experimental results with theoretical models for star polyelectrolytes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Simulating study of atmospheric corrosion of Zn-Al alloy coating in industrial zone: Structure and properties of zinc hydroxysulfate rust particles prepared in the presence of Al(III)

In order to simulate the atmospheric corrosion of Zn-Al alloy coating on the steels in industrial zone, zinc hydroxysulfate (Zn₄(OH)₆(SO₄)·nH₂O: ZHS) rust was artificially synthesized by hydrolyzing the ZnO particles in a mixture of aqueous ZnSO₄ and Al₂(SO₄)₃ solutions and the structure and properties of the products were examined by various means. Then, the atomic ratio X_Al?=?Al(III)/(Zn(II)?+?Al(III)) in the solution was ranged from 0 to 1.0. Adding Al(III) decreased the solution pH before aging to inhibit rust formation. Added Al(III) was easily incorporated in the particles than Zn(II). Increasing X_Al turned the major rust following as hexagonal plate-like ZHS particles?→?hexagonal plate-like Zn-Al layered double hydroxide (LDH) particles?→?cubic Al₆O₅(SO₄)₄·H₂O particles. These rust particles possessed a high adsorption affinity to corrosive CO₂ gas. From these results, it can be supposed that atmospheric corrosion of Zn-Al alloy coating on the steels in industrial district produces the dense and compact rust layer composed of plate-like ZHS and/or Zn-Al-LDH particles owing to their preferred orientation to suppress further corrosion of steels.     

Synthesis and characterization of hyperbranched poly(ethyl methacrylate) by quasi‐living radical polymerization of photofunctional inimer

The hyperbranched poly(ethyl methacrylate)s (PEMAs) were prepared by the quasi‐living radical polymerization of 2‐(N,N‐diethylaminodithiocarbamoyl)ethyl methacrylate (DTCM). DTCM monomer plays an important role in this polymerization system as an inimer that is capable of initiating quasi‐living radical polymerization of the vinyl group. Hyperbranched PEMAs with relatively narrow polydispersity ( M _w/ M _n ≈ 1.6) were obtained. The compact nature of the hyperbranched PEMAs is demonstrated by solution properties which are different from those of the linear analogues. © 2002 Society of Chemical Industry     

Photocatalytic degradation of flexible PVC/TiO2 nanohybrid as an eco-friendly alternative to the current waste landfill and dioxin-emitting incineration of post-use PVC

Photo-degradable poly(vinyl chloride) (PVC)/titanium dioxide (TiO₂) nanohybrid has been investigated to be utilized as an eco-friendly alternative strategy to the current waste landfill and toxic byproduct-emitting incineration of PVC wastes. Thus, the present study suggests a novel idea related to preparing the photocatalytically degradable nanohybrid through TiO₂ nanoparticle-integrated hyperbranched poly(ε-caprolactone) (HPCL-TiO₂). The main aim of this study is to find a solution to the unresolved problem in the conventional PVC/TiO₂ composites related to the poor dispersion of the nanoparticles in PVC polymer. First, TiO₂ nanoparticles are prepared by a sol-gel process, and the size of the particle is about 5-10 nm in diameter as measured by using a transmission electron microscopy (TEM) and dynamic light scattering (DLS). The hyperbranched poly(ε-caprolactone) (HPCL) with numerous COOH groups and good miscibility with PVC as a binder for TiO₂ nanoparticles is prepared from moisture-sensitive catalyst-free polymerization of 2,2-bis[ω-hydroxy oligo(ε-caprolactone)methyl]propionic acids followed by modification reaction using pyridinium dichloromate (PDC), then characterized with ¹H NMR and ¹³C NMR analyses. The integration of TiO₂ nanoparticles onto HPCL is carried out by a dip-coating method based on the spontaneous self-assembly between TiO₂ nanoparticles and HPCL, and the loading amount of the nanoparticles in the HPCL-TiO₂ is determined to be ca. 3.3 wt% by X-ray photoelectron spectroscopy (XPS). Then, the HPCL-TiO₂ is blended with PVC by solution blending in THF as solvent, and the resulting dispersibility of TiO₂ nanoparticle in PVC is characterized by field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectrometry (EDS), which exhibits the TiO₂ nanoparticles are well-dispersed in PVC matrix, while some agglomerates are observed in the PVC/TiO₂ sample prepared from TiO₂ nanoparticle itself. The photocatalytic degradation of the samples are examined and verified from the change of surface morphology, chemical structure, molecular weight, and molecular-level structure after UV irradiation through field-emission scanning electron microscopy (FESEM), UV-visible spectroscopy, gel permeation chromatography (GPC), and positron annihilation lifetime spectroscopy (PALS). The remarkable photocatalytic degradation is observed in the PVC/HPCL-TiO₂, and the structural change accompanied by the degradation of the irradiated sample can clearly explained.     

Temperature effect on ethylene polymerization with a catalyst prepared by mixing Mg(C2H5)(n-C4H9), Al(C2H5)1.5Cl1.5 and iron(II)bis (imino)pyridyl complex

Summary Ethylene polymerization was conducted with a catalyst prepared by mixing 2,6-bis{1-[2,6-(diisopropylphenyl)imino]ethyl}pyridine iron dichloride, Mg(C₂H₅)(n-C₄H₉) and Al(C₂H₅)_1.5Cl_1.5 in the presence of common alkylaluminium as cocatalyst. Both the activity and the molecular weight of polymers produced were markedly dependent upon the polymerization temperature. The end-group analysis of polymers showed that the molecular weight of polymers produced at higher temperature was reduced by chain transfer with Al(C₂H₅)₃ in addition to β-hydrogen elimination.     

Assessment of protective function of steel rust layers by N2 adsorption

The specific surface area (SA) of the rusts formed by exposing various kinds of steels in different situations was determined by N₂ adsorption. The SA values of the rusts increased with the increase of corrosion rate, implying that the rust layers with large SA exhibit a high resistance to corrosion. The suppression of rusting by compact rust layers was interpreted by the blockage of pores in rust layers by the adsorption and capillary condensation of water. The SA values clearly reflect the corrosion levels estimated by the external observation. It was convinced that the SA measurement is a universal quantitative technique to appraisal the protective function of rust layers.     

Nanometer edge profile measurement of diamond cutting tools by atomic force microscope with optical alignment sensor

This paper describes an atomic force microscope (AFM) based instrument for nanometer edge profile measurements of diamond cutting tools. The instrument is combined with an AFM unit and an optical sensor for alignment of the AFM probe tip with the top of the diamond cutting tool edge in the submicrometer range. In the optical sensor, a laser beam from a laser diode is focused to generate a small beam spot with a diameter of approximately 10 μm at the beam waist, and then received by a photodiode. The tool edge top and the AFM probe tip are brought to the center of the beam waist, respectively, through monitoring the variation of the photodiode output. To reduce the influence of the electronic noise on the photodiode output so that the positioning resolution can be improved, a modulation technique is employed that modulates the photodiode output to an AC signal by driving the laser diode with a sinusoidal current. Alignment experiments and edge profile measurements are carried out.     

Capacitive level meter for liquid hydrogen

A capacitive level meter working at low temperatures was made to use in magnetic refrigerator for hydrogen liquefaction. The liquid level was measured from the capacitance between parallel electrodes immersed in the liquid. The meter was tested for liquid nitrogen, hydrogen, and helium. The operation was successful using an AC capacitance bridge. The estimated sensitivity of the meter is better than 0.2 mm for liquid hydrogen. The meter also worked with pressurized hydrogen.     

Development of externally pressurized small-size conical-shaped gas bearings for micro rotary machines

We have developed externally pressurized small-size conical shaped gas bearings for micro rotary machines such as gas blowers, compressors, and medical devices. The bearings are lightweight and enable machines and devices to be downsized by reducing the number of parts, since the journal and thrust loads can be supported by a pair of bearings. The conical bearings (diameters 8 mm and 10 mm) were designed and the manufacturing techniques were considered. The bearing type is a double-row inherent orifice bearing with four feed holes per row. The shape accuracy of the manufactured bearings is within the design limits, being less than 0.005 mm in both roundness and cylindricity. The surface roughness (arithmetic average roughness) of the parts is 0.0002 mm. The static characteristics were calculated and validated by testing on manufactured bearings. Comparative agreement was obtained between the measured and designed values. The proposed calculation method presents as a relatively simple approach for predicting the bearing characteristics. The test rotor exceeded 350 Hz (21,000 rpm) in the rotational test, and whirl vibration was absent. During testing, the maximum rotor vibration amplitude was 0.0125 mm (corresponding to an eccentricity ratio of 0.89).