Swelling of poly(styrene-co-methacrylic acid) latex by isoprene

Carboxylated polystyrene latex was used as seed and isoprene as the second-stage monomer in an inhibited, seeded emulsion polymerization recipe for studies of monomer swelling kinetics at 80°C during interval III of an emulsion polymerization. The isoprene was added to the reactor in small portions using a syringe, and changes in the reactor pressure were continuously measured. Isoprene was added until a free liquid monomer phase was formed; that was, interval II was reached, as indicated by no further pressure increase upon the addition of more monomer. When the observed pressure increment, Op_i, per unit isoprene added was plotted as a function of the volume fraction of polymer in the latex particles, v_p, the graph could be divided into 3 domains. The break points in the Op_i curve could, in an analogous emulsion polymerization, be identified as the glass transition temperature for the polymer, the so-called gel point in interval III and the onset of interval III. In the second domain, where the v_p was between the glass transition temperature, T_g, for the seed polymer and the gel point, the value of Op_i decreased significantly with increasing monomer concentration in the latex particles. This was due to the entropy of mixing and the monomer acting as a plasticizer in the seed polymer. The rate of sorption of monomer to the latex particles was low at high values of v_p. It then increased rapidly with increasing monomer concentrations in the latex particles, [M]_p, and a maximum was observed in domain 2. At lower values of v_p the sorption rate decreased in domain 3 and finally became zero as the free liquid monomer phase started to form. Results from batch polymerization suggested that the rate of diffusion of adsorbed monomer and oligo radicals into the particles was retarded. A simplified form of the Vanzo equation was used to estimate the monomer partitioning. It predicted too high a value of [M]_p, especially in domain 2 of the swelling process. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2041–2051, 1998     

Migration Issues and Strategies for Token Ring

This article considers the problems caused by ever increasing traffic on Token Ring LANs. It shows how the new IEEE 802.5 standard for DTR addresses this problem, outlining scenarios and providing a migration strategy for evolving networks, using this new standard. © 1997 John Wiley & Sons, Ltd.     

The influence of EB-crosslinking on barrier properties of HDPE–mica composites

High-density polyethylene (HDPE) was compounded with untreated and surface-treated mica (10, 20, 40 wt %) and composites were injection-molded. The composites were radiation crosslinked (100, 300, 700 kGy) and hydrocarbon permeability, tensile impact strength, and tensile strength at 25 and 80°C of the composites were examined. The permeability of HDPE decreased from 7 to 3.6 g/(d × m²) by compounding the polymer with 20 wt % mica, and the permeability was additionally reduced to 1.3 g/(d × m²) by irradiation of the compounds (700 kGy). When surface-treated mica was used, the permeability of the composite furthermore decreased to about 1.0 g/(d × m²). Upon irradiation, the E modulus measured at 25°C increased 5% when the dose was 300 kGy. At 80°C, the corresponding increase was 40%. The tensile impact strength of an unfilled polymer increased more than three times by an irradiation dose of 700 kGy, and for a polymer with 10 wt % mica, the tensile impact strength was twice the level of an unirradiated composite. © 1996 John Wiley & Sons, Inc.     

Photopolymerization of dendritic methacrylated polyesters. I. Synthesis and properties

The so-termed starburst dendritic polyesters differ from classical polymers by their structural symmetry, high degree of branching, and high density of terminal functionality. The divergent synthesis of a series of polydisperse dendritic polyesters based upon pentaerythritol and 1,2,4-benzenetricarboxylic anhydride, modified by glycidvl methacrylate and methacrylic anhydride, is described, proceeding in a stepwise growth manner starting from an “initiator core,” building branched arms. These materials have about eight (two samples), 12, or 16 methacrylate double bonds (indicated as D-1-OH, D-1, D-2, and D-3, respectively) at the chain extremities on each molecule. The rheological behavior was investigated by measuring the dynamic viscosity of the dendritic polyesters. The viscosities of the dendritic polyesters largely decrease in the order D-1-OH, D-1, D-2, and D-3 at lower frequency, but the viscosities of D-1-OH and D-1 decrease dramatically at higher frequency. Using a viscometric cup, the flow time of the dendritic methacrylated polyesters was compared with epoxy acrylate-modified unsaturated polyester of a linear type and it was shown that the flow time for the former is only one-third of that for the latter. The thermal mechanical properties and glass transition temperatures of the UV-cured films increase with the degree of terminal functionality. © 1996 John Wiley & Sons, Inc.     

Determination of the detection limit of Ni at the Lund AMS facility by using characteristic projectile X-rays

Accelerator mass spectrometry (AMS) is an ultra-sensitive method for counting atoms, both radionuclides and stable nuclides. When using small tandem accelerators to measure heavy isotopes, interfering isobars are often troublesome. One way to reduce this interference is to combine AMS with the detection of characteristic X-rays of the projectile. After analysis in the AMS system it is possible to identify ions of different atomic number by their characteristic X-rays, by slowing down the ions in a suitable target. In this paper, the detection limit of ⁵⁹Ni at the Lund AMS facility is reported. A method for the chemical extraction of nickel from stainless steel, combined with a purification step to reduce the cobalt content in the sample by several orders of magnitude, is also described.     

Optical and Mechanical Properties of Thin PTFE Films,Deposited from a Gas Phase

Thin polytetrafluoroethylene (PTFE) films are produced by deposition from a gas phase by two methods: electron-enhanced vacuum deposition (EVD) and EVD + low-temperature plasma (LTP). Structure, morphology, and composition of the films are studied by IR spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. They are close to the structure of bulk PTFE. The roughness of the films’ surface is changed with gas pressure and LTP power variations. Films are transparent from UV to near-infrared regions. Refractive and extinction indices and their anisotropy are measured by spectral ellipsometry. They are tuned by variations of deposition conditions. Hardness and Young modulus of the films are increased if EVD + low power LTP is used for film deposition. Use of EVD + LTP also increases thermal stability of the films. Contact angle of the films corresponds to the bulk PTFE. The PTFE molecules oriented are preferentially in perpendicular direction to the substrate surface.