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  • 1
    Electronic Resource
    Electronic Resource
    On the [13C]T1ρ behavior of some elastomers (1997)
    Springer
    Polymer bulletin 38 (1997), S. 333-337 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract. The temperature dependencies of the [13C]T1 ρ NMR relaxation behavior of poly(butyl acrylate), cis-polyisoprene, polychloroprene, and cis-polybutadiene have been studied. The temperature dependence of the relaxation time for each elastomer follows the WLF equation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890050056
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  • 2
    Electronic Resource
    Electronic Resource
    Differences in mineral homeostasis, volumetric bone mass and femoral neck axis length in black and white South African women (1997)
    Springer
    Osteoporosis international 7 (1997), S. 105-112 
    Details
    ISSN: 1433-2965
    Keywords: Bone mass ; Bone turnover ; Ethnic ; Femoral neck axis length ; Mineral homeostasis ; Women
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In South Africa, appendicular and lumbar spine bone mineral density (BMD) have been found to be similar in black and white women. However, femoral BMD has been found to be higher in black than in white women. Two different techniques were used to recalculate BMD to eliminate the possible confounding influence of ethnic differences in height on areal BMD measurements. Volumetric bone mineral apparent density (BMAD) values were calculated and bone mineral content (BMC) was corrected for body and bone size. This report analyses differences in BMD (corrected for height and weight), BMAD, BMC (corrected for body and bone size), femoral neck axis length (FNAL), mineral homeostasis and bone turnover (BT) in a group of 20 to 49-year-old premenopausal (105 whites and 74 blacks) and 45 to 64-year-old postmenopausal (50 whites and 65 blacks) female South African nurses. The corrected BMD and BMC findings were congruous, showing that both pre- and postmenopausal blacks and whites have similar distal radius and lumbar spine bone mass but that whites have lower femoral neck bone mass than blacks. In contrast, BMAD findings suggest that pre- and postmenopausal whites have lower bone mass at the lumbar spine and femoral neck than blacks but similar bone mass at the distal radius to blacks. There is a greater rate of decline in BMD in postmenopausal whites than in blacks. BMD at the femoral neck was 12.1% lower in premenopausal whites and 16.5% lower in postmenopausal whites than in blacks. There was a positive association between femoral neck BMD and weight in premenopausal blacks (R 2=0.5,p=0.0001) but not in whites. Blacks had shorter FNAL than whites in both the pre- and postmenopausal groups. Blacks had lower serum 25-hydroxyvitamin D (25-(OH)D) and higher 1,25-dihydroxyvitamin D (1,25-(OH)2D) levels than whites. There were no ethnic differences in biochemical markers of bone formation (serum alkaline phosphatase and osteocalcin) or bone resorption (urine hydroxyproline and pyridinoline), or in dietary calcium intake in either the pre- or postmenopausal groups. In the postmenopausal group, whites had higher ionized serum calcium (p=0.003), similar serum albumin, lower serum parathyroid hormone (p=0.003) and higher urinary calcium excretion (p=0.0001) than blacks. These results suggest that the higher peak femoral neck BMD in South African blacks than in whites might be determined by greater weight-bearing in blacks and that the significantly lower femoral neck BMD in postmenopausal whites than in blacks is determined by lower peak femoral neck BMD and a faster postmenopausal decline in BMD in whites. The higher incidence of femoral neck fractures in South African whites than in blacks is probably determined by the lower femoral neck BMD and longer FNAL in whites. The greater rate of decline in BMD in postmenopausal whites than in blacks is associated with an increase in urinary calcium excretion in whites. Measurement of biochemical markers of BT has not contributed to the understanding of ethnic differences in BMD and skeletal metabolism in our subjects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01623684
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  • 3
    Electronic Resource
    Electronic Resource
    Integrated Management Strategies for Amblyomma Americanum (Acari: Ixodidae) in Non-Agricultural Areas (1999)
    Springer
    Experimental and applied acarology 23 (1999), S. 827-839 
    Details
    ISSN: 1572-9702
    Keywords: Amblyomma americanum ; lone star tick ; integrated management ; modeling ; computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The simulation model LSTSIM was revised and adapted to estimate the effects of different management strategies on populations of the lone star tick, Amblyomma americanum (Linnaeus), in non-agricultural areas. The control technologies evaluated were area-wide acaricide application, acaricide self-treatment of white-tailed deer, vegetation reduction and reductions in the density of white-tailed deer. Estimated changes in tick populations using these technologies compared favorably with results from actual integrated tick management studies at five different geographic locations. Area-wide acaricide application and vegetation reduction, as well as combinations of the two technologies proved to be useful for short-term, seasonal management of ticks in small non-agricultural areas and residential sites. Self-treatment of deer with acaricide, applied topically or as a systemic, appears to be the most cost-effective technology for use in area-wide, long-term programs for tick control. The results of simulations suggest that reductions in deer density should be considered as a component of any tick management program.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006262216124
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  • 4
    Electronic Resource
    Electronic Resource
    Compatibilization of the PBA/PMMA core/shell latex interphase. I. Effect of PMMA macromonomer (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 3173-3181 
    Details
    ISSN: 0887-624X
    Keywords: macromonomer ; core/shell latexes ; interphase ; compatibilizing agent ; NMR relaxation studies ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work poly(methyl methacrylate) (PMMA) macromonomer is used as a compatibilizing agent in a poly(butyl acrylate) (PBA)/PMMA core/shell latex system. The incorporation of the PMMA macromonomer was achieved by copolymerizing it with BA monomer using miniemulsion polymerization. PBA seed latex was also synthesized without the macromonomer present to compare the compatibilizing effects with the PMMA macromonomer. The second stage methyl methacrylate monomer was added semi-continuously to the PBA seed latexes under monomer-starved conditions. Solid-state 13C-NMR [H]T1ρ relaxation studies were used to determine the effect of PMMA compatibilizer on these PBA/PMMA core/shell latex interphase regions. The thickness of the interphase of the core/shell particles prepared with and without the PMMA macromonomer compatibilizing agent are calculated to be in the range of 15-16 nm and 10-12 nm, respectively. Electron microscopy revealed that the seed latex prepared with the PMMA macromonomer achieved a more uniform coverage with the second stage PMMA polymer as compared to the latex synthesized without the compatibilizing agent present. It is concluded that the PMMA macromonomer is effective in increasing the thickness of the interphase region and also the amount of interfacial PMMA. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Compatibilization of the PBA/PMMA Core/Shell Latex Interphase. II. Effect of PMMA Macromonomer (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 3183-3190 
    Details
    ISSN: 0887-624X
    Keywords: macromonomer ; core/shell latexes ; interphase ; compatibilizing agent ; NMR relaxation studies ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work poly(methyl methacrylate) (PMMA) macromonomer is used as a compatibilizing agent in a poly(butyl acrylate) (PBA)/PMMA core/shell latex system. The incorporation of the PMMA macromonomer was achieved by copolymerizing it with BA monomer using miniemulsion polymerization. PBA seed latex was also synthesized without the macromonomer present to compare the compatibilizing effects with the PMMA macromonomer. The second stage methyl methacrylate monomer was added semi-continuously to the PBA seed latexes under monomer-starved conditions. Solid-state 13C-NMR [H]T1ρ relaxation studies were used to determine the effect of PMMA compatibilizer on these PBA/PMMA core/shell latex interphase regions. The thickness of the interphase of the core/shell particles prepared with and without the PMMA macromonomer compatibilizing agent are calculated to be in the range of 15-16 nm and 10-12 nm, respectively. Electron microscopy revealed that the seed latex prepared with the PMMA macromonomer achieved a more uniform coverage with the second stage PMMA polymer as compared to the latex synthesized without the compatibilizing agent present. It is concluded that the PMMA macromonomer is effective in increasing the thickness of the interphase region and also the amount of interfacial PMMA. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1996.869
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of core/shell ionomeric latexes. I. Latex and film properties (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 301-311 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This research work involved studies on the synthesis and characterization of core/shell ionomeric latexes in order to understand the process of ionic aggregate formation. The core/shell structure of the ionomeric latexes prepared in this study confines the ionic domains to the copolymeric matrix within the shell polymer, and in addition, benefits from the ionomeric properties and core/shell structure simultaneously. Core/shell ionomeric latexes with polystyrene cores and styrene/n-butyl acrylate/methacrylic acid terpolymer shells were synthesized by a semicontinuous seeded emulsion copolymerization process. The distribution of the methacrylic acid in the core/shell latexes was determined using conductometric titration techniques. The results of the conductometric titration analysis indicate that the principal locus of the carboxyl groups in the core/shell latexes is at the particle surface, but specific information about the differences in the distribution of methacrylic acid inside the latex particles could not be obtained. Mechanical characterization of the core/shell ionomeric latex films was carried out to understand the structure-property relationships using Dynamic Mechanical Analysis (DMA) and tensile testing. It was discovered that the core/shell latexes exhibited significantly different properties, owing to the differences in the overall carboxyl content and surface loading. Extensive studies were carried out to study the effect of water plasticization on the mechanical behavior of the core/shell ionomeric latex films; water adsorption causes the solvation of ionic aggregates. A preliminary investigation of the effect of the type of counterion used for the neutralization of carboxyl groups on the properties of core/shell ionomeric latex films was also carried out. © 1995 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070580210
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of the interphase in poly(divinylbenzene)/poly(N-butyl acrylate) core/shell latexes by high-resolution solid-state NMR relaxation studies (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 323-330 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Poly(divinylbenzene)/poly(n-butyl acrylate) core/shell latexes were investigated using solid-state 13C-NMR. The (H)T1ρ relaxation time was found to be substantially affected by many of the seeded emulsion polymerization parameters, such as the core/shell ratio, the mode of addition of the second-stage monomer, the addition rate of the second-stage monomer, and the level of conversion of the seed latex at the time of addition of the second-stage monomer. The existence of an interphase region between the core and shell polymers was detected. Maximum interphase region thickness was achieved when the butyl acrylate was added under starved conditions. The thickness of this interphase layer was calculated to be 5-7 nm based on a model proposed by McBriety.1 Solid-state NMR was found to be an excellent spectroscopic technique to probe the interphase region in core/shell latexes. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070580212
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of core/shell ionomeric latexes. II. Surface analysis by X-ray photoelectron spectroscopy (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 313-322 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: It is generally accepted that conductometric titration is a time-dependent technique in the case of highly carboxylated latexes because of the changes in the structure of the particle surface resulting from the neutralization and the alkali swellability imparted by the carboxyl groups when titrated with an alkali. At high levels of neutralization, the diffusion of the hydroxyl groups into the shell will be much faster than at the lower levels of neutralization. Due to this changing rate of the diffusion of the hydroxyl groups into the highly alkaliswellable copolymer shell, the assignment of the carboxyl groups to the different sublevels inside the particle shell can, at best, be arbitrary. To overcome this handicap, x-ray photoelectron spectroscopy (XPS or ESCA) was used to obtain the depth profile of methacrylic acid near the surface of the particles. It is expected that by accurately characterizing the surface loading of the carboxyl groups, it will be possible to control the microphase separation process of the system. Considering the high concentration of the carboxyl groups on the surface of the core/shell latexes prepared in this study, XPS experiments were conducted to obtain the depth profile of the carboxyl groups. Angle-dependent XPS studies were performed on films derived from the core/shell latexes with different amounts of methacrylic acid in the shell layer in order to determine the compositional heterogeneities between the surface and subsurface layers. In addition, x-ray photoelectron spectroscopy was used to study the changes in the surface composition of solvent-cast core/shell latex films prepared in this study upon treatment with alkali solution. It was discovered that a large-scale migration of the carboxyl groups could occur as a result of coulombic interactions. © 1995 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070580211
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  • 9
    Electronic Resource
    Electronic Resource
    Interfacial aspects of strength development in poly(methyl methacrylate)-based latex systems (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 367-374 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Film formation from poly(methyl methacrylate) (PMMA) latex and PMMA copolymer latex incorporating N-(iso-butoxymethyl)acrylamide (IBMA) or methacrylic acid (MAA) has been investigated in terms of the development of tensile strength as a function of annealing time and temperature. Tensile strength is developed through a combination of macromolecular interdiffusion and interfacial crosslinking. The relative rates of interdiffusion vs. crosslinking reactions were studied as a function of temperature and the chemical nature and concentration of the IBMA and MAA functional groups. For low concentrations of these two functional monomers it appears that polymer chain interdiffusion between adjacent latex particles during the film formation process dominates the kinetics of strength development. However, at higher IMBA and MAA concentrations, the higher glass transition temperature at the latex particle surface and intraparticle crosslinking hinders interdiffusion, as reflected by differences in the power law exponent values obtained from the log-log dependence of tensile strength on annealing time. The power law exponents were higher in the case of PMMA than for both IBMA- and MAA-containing copolymers. There was a greater influence temperature on the tensile behavior for the MAA copolymer system as compared to the IBMA copolymer. In the interfacially crosslinked latex polymer system, there is competition between the interdiffusion and crosslinking mechanisms in determining the final mechanical strength of films during the annealing process. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070580216
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  • 10
    Electronic Resource
    Electronic Resource
    Emulsion terpolymerization of dimethyl meta-isopropenyl benzyl isocyanate (TMI®) with acrylic monomers: Process development and kinetics (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 61 (1996), S. 911-921 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dimethyl meta-isopropenyl benzyl isocyanate (TMI®) is a bifunctional monomer possessing a double bond and an isocyanate group. Emulsion terpolymerization of TMI with the acrylic monomers, methyl methacrylate and n-butyl acrylate, was studied. Polymerizations were carried out at 40°C using a redox initiator system in order to minimize the extent of hydrolysis of the isocyanate in the aqueous emulsion environment. The kinetics of the polymerization reaction were investigated. The polymerization rate was found to decrease with increasing TMI concentration. The effects of several preparative variables such as the monomer, surfactant, and initiator concentration on the polymerization kinetics was studied. Several semicontinuous polymerization processes were developed in order to enhance the incorporation of TMI at appreciable rates. These processes also allow us to control the polymer composition, latex particle size, and the locus of isocyanate groups in the latex particle. Process variables such as the mode of initiator addition (batch versus semicontinuous) were found to greatly influence the polymerization behavior. © 1996 John Wiley & Sons, Inc.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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