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  • 11
    Electronic Resource
    Electronic Resource
    Study on the relationship between the mechanical properties and processing for self-reinforced polymers. Part 1: A theory of stress-induced crystallization for entangled polymer networks (1993)
    Springer
    Colloid & polymer science 271 (1993), S. 911-929 
    Details
    ISSN: 1435-1536
    Keywords: Stress-induced crystallization ; self-reinforced polymers ; entangled polymer networks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A new theory of stress-induced crystallization for entangled polymer networks is presented. It is based on the theory of viscoelasticity with constraints of trapped entanglements and crystallites using a model of fibrillar and lamellar morphology engendered by the extended and folded-chain crystallization. The probability distribution function of the end-to-end vector for two kinds of constituent chains and the viscoelastic free energy of deformation for two kinds of networks have been calculated. The relationships of stress to strain for four types of deformation were derived. The theory is successful in relating the equilibrium degree of crystallinity and the melting temperature to the extension ratio for networks with stress-induced crystallization. Furthermore, the theory provides a theoretical foundation for studying the dependences of tensile modulus and strength on the processing and testing conditions for self-reinforced polymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00654851
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  • 12
    Electronic Resource
    Electronic Resource
    Should the removal of water be taken into account in the analysis of kinetic data of polyesterification reactions? (1992)
    Springer
    Polymer bulletin 28 (1992), S. 351-354 
    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: Summary In most polyesterification reactions, the concentrations of acid, alcohol and catalyst (if present) are expressed in moles per unit mass of the charge, denoted as moles/kg. In this paper, a general kinetic equation that takes water removal into account has been derived. It has been shown that (i) when the progress of reaction is followed by titration of acid, the removal of water affects the concentrations of alcohol and catalyst; and (ii) the ratio of the rate constants that do and do not account for water removal is smaller than unity, and it varies with the degree of reaction. On the other hand, it has been found that the rate constant obtained using moles/kg as the unit of concentration is not a real constant but a function of the charge density. Treating it as a constant may lead to appreciable error or misinterpretation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00294834
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  • 13
    Electronic Resource
    Electronic Resource
    Novel ultrasonic fusion imaging method based on cyclic variation in myocardial backscatter (1992)
    Springer
    Medical & biological engineering & computing 40 (1992), S. 163-167 
    Details
    ISSN: 1741-0444
    Keywords: Cardiac ischaemia ; Cyclic variation in integrated backscatter ; Fusion image ; Integrated backscatter ; Myocardium ; Ultrasound
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Quantitative ultrasonic tissue characterisation of the myocardium based on integrated backscatter (IB) has the potential of becoming an effective method for detecting and evaluating myocardial ischaemia. To facilitate IB-based clinical applications, a new imaging method has been developed that combines the anatomical information of a B-mode image with the contractile performance of a selected myocardial region. To produce such a fusion image, a region of interest (ROI) in a B-mode cardiac image was first selected by the user. Algorithms for detection of the endocardium andepicardium were developed, and the resulting mean distance between the computer-detected curve and the manually traced curve was 0.83 mm for the endocardium and 0.58 mm for the epicardium. The cyclic variation of IB (CVIB) of each myocardial tissue element within the ROI was then calculated over one cardiac cycle. Finally, a grey-scale B-mode image at the end of diastole was displayed as a still image, and the pixels representing the myocardial tissue in the ROI colour-coded according to the corresponding CVIB over the past heart cycle. Both the B-mode image and the colour-coded region were refreshed (up-dated) at the next end-of-diastole. Preliminary results from normal (CVIB=10–12dB) and ischaemic (CVIB=5–7 dB) canine hearts are presented that demonstrate the utility of this new imaging method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02348120
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  • 14
    Electronic Resource
    Electronic Resource
    Monoesterification of styrene-maleic anhydride copolymers with alcohols in ethyl benzene: Catalysis and kinetics (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 691-700 
    Details
    ISSN: 0887-624X
    Keywords: monoesterification ; maleic anhydride copolymers ; catalysis ; kinetics ; chemical equilibrium ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A kinetic investigation on the monoesterification reaction of the maleic anhydride residue (MA) in styrene-maleic anhydride copolymers with aliphatic alcohols was carried out in ethyl benzene solution. By comparison to classic catalysts such as tributylamine (TBA) and pyridine, 4-dimethylaminopyridine (4DMAP) is by far the most effective catalyst for this reaction. While both general base and nucleophilic mechanisms contribute to the reaction catalyzed by TBA or pyridine, a nucleophilic mechanism prevails with 4DMAP. This reaction is reversible, and its chemical equilibrium constant decreases significantly with increasing temperature. Both kinetic and thermodynamic results showed that in the presence of 4DMAP, the forward and reverse reactions are second and first order, respectively. The existence of side reactions, reactivity of two styrene-maleic anhydride copolymers of different MA contents as well as two aliphatic alcohols of different lengths are also addressed. © 1993 John Wiley & Sons, Inc.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1993.080310313
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  • 15
    Electronic Resource
    Electronic Resource
    Catalytic aminolysis of acrylic copolymers in solution and in the melt. II. Comparison between styrenic and ethylenic copolymers (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 635-641 
    Details
    ISSN: 0887-624X
    Keywords: aminolysis ; catalysis ; mechanism ; kinetics ; tautomeric compound ; melt ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aminolysis of poly(styrene-co-methyl acrylate) (SMA) by octadecylamine in solution and in the melt has been reported in Part I. We now have studied the aminolysis of poly(ethylene-co-methyl acrylate) (EMA) with the same amine in the melt and compared the two sets of data in this paper. With EMA, the data confirmed and precised the catalytic mechanism proposed in Part I. The best tautomeric catalysts are the ones which form an eight-atom ring structure with the ester and amine groups. With EMA aminolysis is faster than with SMA because of the steric hindrance of phenyl groups in SMA. But EMA aminolysis remains a rather slow reaction. In a corotating twin-screw extruder the conversion was only around 4% at 220°C with a mean residence time of 150 s. It was also shown that the EMA/octadecylamine/catalyst system, like the SMA system, is homogeneous in the molten state at temperatures around 200°C.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300415
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  • 16
    Electronic Resource
    Electronic Resource
    Catalytic aminolysis of acrylic copolymers in solution and in the melt. I. Mechanism and kinetics (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 625-634 
    Details
    ISSN: 0887-624X
    Keywords: catalysis ; mechanism ; kinetics ; aminolysis ; tautomer ; molten state ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aminolysis of poly(styrene-co-methyl acrylate) (SMA) by octadecylamine was studied in solution and in the melt at temperatures around 200°C. This reaction is rather slow, so several types of catalysts were tested to accelerate it. The most efficient is 2-pyridone, a compound in tautomeric equilibrium with 2-hydroxypyridine. A mechanism of the catalytic reaction is proposed whereby the tautomeric nature of the catalyst plays a key role in a very important step of the reaction, namely the proton transfer. This mechanism is confirmed by the kinetic data determined in a 1,2,4-trichlorobenzene solution and in the melt. In addition, it was found that the kinetic data obtained in both media are very close, indicating no significant difference of local polarity in the two reaction media. Data also show only a minor effect due to difference in viscosity. Finally, the question of the homogeneity of the molten medium is discussed.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300414
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  • 17
    Electronic Resource
    Electronic Resource
    Acceleration of chemical reaction in boiling polymer solutions (1993)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 653-662 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This article discusses the effect of boiling inert hydrocarbon solvent on the model second-order transesterification reaction of ethylene/vinyl acetate copolymer with 3-phenyl 1-propanol. In the presence of boiling, the overall reaction rate increases substantially due to mass-transfer effects in the proximity of the vapor-liquid interface. The present experiments and theory indicate that during the lifetime of a bubble in the boiling medium, the concentrations of reactants and the catalyst increase significantly near the bubble surface due to the rapid diffusion of the inert solvent. After the bubble rupture, the concentration differences persist and continue affecting the chemical reaction rate. The combination of these effects is responsible for the apparent increase in the overall reactivity.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690390414
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  • 18
    Electronic Resource
    Electronic Resource
    Photopolymerization of methyl methacrylate using benzoin isopropyl ether as photoinitiator: Effect of thiophenol compounds (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 47 (1993), S. 1665-1672 
    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: Effects of a series of thiophenols R—ArSH with substituting groups R in the para-position and 2-mercaptobenzoic acid on the kinetics of polymerization of methyl methacrylate (MMA) photoinitiated by benzoin isopropyl ether (BIPE) were investigated using an autorecording dilatometer. Thiophenols were found to have a dual effect on polymerization: reducing induction time and accelerating rate of polymerization. A mechanism was proposed suggesting that this increased rate of polymerization and reduced induction time with addition of a thiophenol is due to the fact that, instead of consuming radicals, the dissolved oxygen in the MMA/BIPE system can be converted into active radicals through effective photooxidation of the thiophenol. Although the maximum increase in rate of polymerization is of a minor difference between various thiophenol compounds, reduction in induction time is strongly dependent on the nature of substituting groups in the following order: —CH3 〉 —CH(CH3)2 〉 —OCH3 or —Cl 〉 —H. 2-Mercaptobenzoic acid, on the other hand, increases induction time and decreases rate of polymerization. © 1993 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070470914
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  • 19
    Electronic Resource
    Electronic Resource
    Transesterification reaction of poly(ethylene-co-vinyl acetate) with alcohols: A kinetic study in solution and in the bulk (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 46 (1992), S. 1039-1044 
    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: The chemical kinetics of the transesterification reaction of poly(ethylene-co-vinyl acetate) (EVA) with aliphatic alcohols were investigated, both in solution and in bulk, in the presence of dibutyl tin dilaurate (DBTDL) as the catalyst. A Fourier Transform infrared spectrometer (FTIR) was utilized for the measurement of the extent of the reaction. Experimental results showed that the reaction carried out in solution and in the bulk follows the same mechanism, namely, a reversible second order reaction of which the equilibrium only slightly increases with temperature. Additionally, the overall forward and reverse rate constants are proportional to the square root of the concentration of the catalyst. This study has also revealed that the intrinsic rate constants in solution and in the bulk are the same, regardless of the differences in the physical conditions encountered in the bulk and solution media, in particular, the reactant concentrations and viscosity of the reacting mixture. The effects of mechanical mixing are unimportant, since the reaction rate is relatively slow as compared with the rate of diffusion.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070460612
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  • 20
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    Angiogenin promotes invasiveness of cultured endothelial cells by stimulation of cell-associated proteolytic activities. (1994)
    National Academy of Sciences
    Details
    Publication Date: 1994-12-06
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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