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  • 1990-1994  (20)
  • 1991  (20)
  • Chemistry  (19)
  • Life and Medical Sciences  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Dynamics of a cascade of two continuous stirred tank polymerization reactors with a binary initiator mixture (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 333-352 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 dynamic behavior of two continuous stirred tank reactors in series has been investigated for free radical solution polymerization of styrene with a binary mixture of two initiators having different thermal decomposition activities. For a wide range of initiator feed composition, both reactors exhibit quite complex nonlinear steady state and transient behavior. When the reactor residence time is used as a bifurcation parameter, the second reactor can have up to five steady states. For certain range of reactor operating conditions, bifurcations to various types of periodic solutions have been observed, such as Hopf bifurcation, isolas, period doubling, period-doubling cascade, and homoclinics. The effects of other reactor variables, such as total initiator concentration, coolant temperature, and reactor volume ratio on the reactor dynamics, are illustrated to show the complex dynamic behavior of the two-reactor system catalyzed by a mixture of t-butyl perbenzoate and benzoyl peroxide.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760310506
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  • 2
    Electronic Resource
    Electronic Resource
    An investigation into the nature of the electrochemical and surface properties of polyacrylamides and a study of their adsorption onto the surface of papermaking woodpulps using alternating-current polarography (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 2875-2893 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A cationic polyacrylamide was examined using polarography, constant potential coulometry, photon correlation spectroscopy, electrocapillarity and potentiometric titrimetry. A polarographic response was found in differential-pulse polarography (DPP), direct-current and Kalousek modes at -1,7 V versus a silver/silver chloride electrode. In each case the magnitude of the response was a function of polymer concentration. However, it is thought that the response is not due to the polymer itself but impurities found with it. These were found to have a pK of 4,75. The polymer appears to develop a more open structure in LiCl solution (〈0,0013 mol/L). The unwashed polymer was found to greatly increase the interfacial tension at the mercury drop, but this effect was considerably reduced on washing the polymer in 70% acetone solution. Hydrolysis of the polymer seems to occur at pH 10. The suppression of the negative tensammetric peak of poly(ethylene glycol) (PEG200) by a range of cationic polyacrylamides was used for their analysis in the determination of their adsorption onto the surface of woodpulp. The adsorption was found to be a function of both their cationicity and mean molar mass. The rate of hemicellulose desorption from the woodpulp appears to be pH dependent. The impurity is thought to be mainly adipamic acidSystematic name: 5-carbamoylpentanoic acid..
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021921204
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  • 3
    Electronic Resource
    Electronic Resource
    The measurement of concentration and stability of weak acids and a study of the ionisation of polysaccharides using buffer capacity curves (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1741-1748 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A technique using buffer capacity has been developed for evaluating the approximate pK values of the stability constant K, of polyelectrolytes. The technique has been applied to hemicellulose extracted from woodpulp (pK ≈ 3,9 (0,1 M NaCl)) and dextran (pK = 13,55 ± 0,2 (2 M NaCl)). Verification of the method has been obtained by applying it to acetic acid (pK = 4,55 ± 0,02 (0,1 M NaCl), pK = 4,70 ± 0,02 (0,001 M NaCl)) and glucose (pK = 12,00 ± 0,05 (2 M NaCl)). Glucose was found to turn peppermint green in NaOH solutions. At least 50% of the surface charge of woodpulp was found to originate from its hemicellulose coating.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021920808
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  • 4
    Electronic Resource
    Electronic Resource
    Polymer precursor synthesis of alumina fibers (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 495-503 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High strength alumina fibers were fabricated with a polymer precursor process which was monitored with 13C-NMR, elemental analysis, gas evolution, SEM, and X-ray diffraction. Methylaluminoxane was chain extended by reaction with H2O, the unreacted methyl groups were converted to propanoyloxyl and i-propanoyl groups in molar ratios of 0.2 : 0.8 to 0.4 : 0.6 to afford spinning dope of adequate fluidity which can be spun into filaments with suitable stability. These precursor fibers were hydrolyzed in two stages at ambient temperatures and at 320-350°C, and then calcined at 950°C. The resulting alumina fibers have average tensile strengths up to 1.1 GPa and modulus of greater than 140 GPa.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080290406
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  • 5
    Electronic Resource
    Electronic Resource
    Olefin copolymerization with metallocene catalysts. III. Supported metallocene/methylaluminoxane catalyst for olefin copolymerizationFor Parts I and II, see References 1. (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1603-1607 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Supported catalyst for fluidized bed polymerization processes has been prepared by reacting macroporous SiO2 first with MAO (methylaluminoxane) and then with Et [Ind]2ZrCl2. It contains 0.60 wt % of Zr and an [Al]/[Zr] ratio of 50. This catalyst produces homogeneous E/P (ethylene/propylene) copolymers with truly random copolymerization behaviors and required to achieve the same copolymerization activity for the Et[Ind]2ZrCl2/MAO would be required a total [Al]/[Zr] of only 670. Several time larger amount of MAO would be required to achieve the same copolymerization activity for the Et [Ind]2ZrCl2/MAO catalyst in solution. This random copolymerization is independent of catalyst concentration and composition. Activation of the supported catalyst with i-butylaluminoxane, tri-i-butylaluminum, or trimethylaluminum resulted in lower activity and copolymers having high ethylene content and crystallinity.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080291109
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  • 6
    Electronic Resource
    Electronic Resource
    Solvay type VCl3 isospecific catalysts (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1807-1817 
    Details
    ISSN: 0887-624X
    Keywords: VCl3 ; propylene polymerization ; Ziegler-Natta catalyst ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvay type S-VCl3 catalyst has 7% of catalytically active vanadium sites ([C*]) with kp (rate constant of propagation) = 31 (M s)-1 for ethylene polymerization. Addition of a comonomer, propylene of 4-methylpentene-1 (4-MP) significantly raised the ethylene polymerization activity. S-VCI3 catalyst has very small amounts of catalytically active vanadium for propylene polymerizations: [Ci*] = 0.19% with kp,i = 857 (M s)-1 and [Ca*] = 0.45% with kp,a = 23 (M s)-1 for isospecific and nonspecific sites, respectively. Addition of a conomer, ethylene or 4-MP. lowered the propylene polymerization activity. S-VCI3 is more easily reduced to the divalent ion by AIR3 than S-TiCl3. Methyl-p-toluate moderates the reducting power of AIR3; it increase the productivity and stereoselectivity of the S-YiCl3 catalyst, VCI3 supported on MgCl2 (CW-V catalyst) has enhanced rate constant of propylene polymerization but has the opposite effects on the S-TiCl3 Catalyst. VCI3 supported on MgCl2 (CW-V catalyst) has enhances rate constant of propylene polymerization but only a minute fraction of the supported vanadiums are catalytically active: [Ci*] = 0.019% and kp,i = 1580 (Ms)-1, [Ca*] = 0.057% and kp,i = 58 (M s)-1. This is compared with far greater number of catalytically active titanium sites in the TiCl3 supported on MgCl2 catalyst: [Ci*] = 6% and kp,i = 200 (M s)-1, [Ca*] = 6% and kp,a = 16(M s)-1. Therefore, both the S-VCI3 and CW-V catalysts are highly stereoselective but low in efficiency with respect to the utilization of the vanadium ion in the catalysis.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080291213
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  • 7
    Electronic Resource
    Electronic Resource
    Olefin copolymerization with metallocene catalysts. I. Comparison of catalysts (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1585-1593 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A number of metallocene/methylaluminoxane (MAO) catalysts have been compared for ethylene/propylene copolymerizations to find relationship between the polymerization activities, copolymer structures, and copolymerization reactivity ratio with the catalyst structures. Stereorigid racemic ethylene bis (indenyl) zirconium dichloride and the tetrahydro derivative exhibit very high activity of 10 7 g (mol Zr h bar)-1, giving copolymers having comonomer compositions about the same as the feed compositions, molecular weights increasing with the increase of ethylene in the feed, random incorporation of comonomers, and narrow molecular weight distribution indicative of a single catalytic species. Nonbridged bis (indenyl) zirconium behaved differently, favoring the incorporation of ethylene over propylene, producing copolymers whose molecular weight decreases with the increase of ethylene in the feed, broad molecular weight distribution, and a methanol soluble fraction. This catalyst system contains two or more active species. Simple methallocene catalysts have much lower polymerization activities. CpTiCl2/MAO produced copolymers with tendency toward alternation, whereas Cp2HfCl2/MAO gave copolymer containing short blocks of monomers.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080291107
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  • 8
    Electronic Resource
    Electronic Resource
    Kinetics and stereochemical control of propylene polymerization initiated by ethylene bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride/methyl aluminoxane catalystPart XI of the series on homogenous Ziegler-Natta catalysts. See Ref. 1 for further information. (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 459-470 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics and sterochemical control of propylene polymerization initiated by rac-ethylene bis (4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride/methyl aluminoxane (1/MAO) and by rac-ethylene bis (1-indenyl) zirconium dichloride/MAO (2/MAO) were investigated. The polymerization activities increase monotonically with temperature corresponding to an overall activation energy of 10.6 kcal mol-1. This is accompanied, however, by reduction of stereochemical control as reflected in the amount of the polypropylene (PP) soluble in low boiling solvent. At a temperature of 30°C and higher, polymerization initiated by 1/MAO produced no PP insoluble in refluxing n-heptane. Tritium radiolabeling showed that at [Al]/[Zr] ≥ 3500 and 30°C, two-thirds of 1 becomes catalytically active. There are at least two kinds of active species formed in about equal amounts; one has more stereoselectivity, 10-20 times greater rate constant of propagation, and a factor of 5-15 faster chain transfer to MAO than the second kind of Active species. This is also true at low [Al]/[Zr] of 350, except that the total amount of the two active species corresponds to only 13% of the [1]. Replacement of MAO with trimethyl aluminum resulted in the decrease of stereoselectivity and loss of catalytic activity proportional to the amount of replacement. A comparison was made with the polymers obtained with 2/MAO.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080290402
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  • 9
    Electronic Resource
    Electronic Resource
    Syndiospecific polymerization of styrene. II. Monocyclopentadienyltributoxy titanium/methylaluminoxane catalyst (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1253-1263 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syndiospecific polymerization of styrene was catalyzed by monocyclopentadienyltributoxy titanium/methylaluminoxane [CpTi (OBu)3/MAO]. The atactic and syndiotactic polystyrenes were separated by extracting the former with refluxing 2-butanone. The activity and syndiospecificity of the catalyst were affected by changes in catalyst concentration and composition, polymerization temperature, and monomer concentration. Extremely high activity of 5 × 107 g PS (mol Ti mol S h)-1 with 99% yield of the syndiotactic product were achieved. The concentration of active species, [C*], has been determined by radiolabeling. The amount of the syndiospecific and nonspecific catalytic species, [C*s] and [C*a] respectively, correspond to 79 and 13% of the CpTi(OBu)3. The rate constants of propagation for C*s and C*a at 45°C are 10.8 and 2.0 (M s)-1, respectively, the corresponding rate constants for chain transfer to MAO are 6.2 × 10-4 and 4.3 × 10-4s-1. There was no deactivation of the catalytic species during a batch polymerization. The rate constant of chain transfer with monomer is 6.7 × 10-2 (M s)-1; the spontaneous β-hydride transfer rate constant is 4.7 × 10-2 s-1. The polymerization activity and stereospecificity of the catalyst are highest at 45°C, both decreasing with either higher or lower temperature. The stereoregular polymer have broad MW distributions, M̄w/M̄n = 2.8-5.7, and up to three crystalline modifications. The Tm of the s-PS polymerized at 0-90°C decreased from 261.8 to 241°C indicating thermally activated monomer insertion errors. The styrene polymerization behaviors were essentially insensitive to the dielectric constant of the medium.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080290904
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  • 10
    Electronic Resource
    Electronic Resource
    Syndiospecific polymerization of styrene. I. Tetrabenzyl titanium/methylaluminoxane catalyst (1991)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 29 (1991), S. 1243-1251 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syndiospecific polymerization of styrene (S) was catalyzed by Bz4Ti/MAO (tetrabenzyltitanium/methylaluminoxane). The product was separated into syndiotactic polystyrene (s-PS) and atactic polystyrene (a-PS) by extraction of the latter with boiling 2-butanone. Over the broad range of catalyst concentrations, compositions, and polymerization temperatures, the catalytic activity is 150 ± 80kg PS (mol Ti mo S h)-1 with 89 ± 5% yield of s-PS (SY). The concentration of active species has been determined by radiolabeling. Only about 1.7% of Bz4Ti initiates syndiospecific polymerization at 60°C with values of rate constants for propagation and for chain transfer to MAO of 1.38 (M s)-1 and 5.2 × 10-4s-1, respectively. Nonspecific polymerization was initiated by 16.8% of the Ti having values of 0.056 (M s)-1 and 6.5 × 10-4 s-1 for the rate constants of propagation and transfer, respectively. The effect of solvent polarity on the polymerization was studied using toluene mixed with chlorobenzene of o-dichlorobenzene as solvents. An increase of effective dielectric constant from 2.43 to 5.92 reduces the polymerization activity by a factor of two and lowers SY to mere 39%. In 1 : 1 toluene/chlorobenzene solvent mixture, it was found that 1.3% and 26% of the Bz4Ti initiate syndiospecific and nonspecific polymerizations of styrene, respectively. The Bz4Ti/MAO catalyst is poor in both productivity and stereoselectivity.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1991.080290903
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