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  • Chemistry  (10)
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  • 1
    Electronic Resource
    Electronic Resource
    Temperature effect on the stereoelective polymerization of methylthiirane in homogeneous phase (1981)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 182 (1981), S. 2225-2231 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Chiral cadmium thiolates of cysteine with cyclohexyl or (-)menthyl ester groups were prepared and compared with similar compounds (with isopropyl or methyl ester groups) as initiators for stereospecific polymerization of methylthiirane in homogeneous phase. The resulting polymers are highly isotactic and in all cases stereoelection can be reversed with a small change in polymerization temperature. This temperature effect permitted to differentiate two stages in the polymerization corresponding to the formation of a precursor and to that of a high polymer, respectively.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1981.021820812
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  • 2
    Electronic Resource
    Electronic Resource
    Role of cocatalysts in polymerizations initiated with benzyl derivatives of transition metals, 1. Polymerization of ethylene (1983)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 184 (1983), S. 1389-1395 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymerization of ethylene initiated in naphta solution by Zr(CH2C6H5)4 at 200°C under high purity conditions showed a cocatalytic effect of water with a maximum rate for a mole ratio H2O/Zr close to 0,1. No activity was observed for the hypothetical compound (C6H5CH2)3ZrOZr(CH2C6H5)3. Ethylene polymerization was also initiated with supported catalysts obtained by reaction of Zr(CH2C6H5)4 with silicium oxide or pre-dried aluminium oxide with an increase of activity (by a factor of 5). The resulting polyethylenes were found to be virtually linear with 1,5 CH3 groups for 1000 C atoms and with melting points of 134 - 136,5°C. They have high molecular weights with very broad distribution. These results were interpreted by a mechanism involving Ziegler-like active centers.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1983.021840707
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  • 3
    Electronic Resource
    Electronic Resource
    Stereospecific polymerization of methylthiirane in homogeneous phase, 4. Solvent effect on stereospecificity and enantioasymmetry (1993)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 194 (1993), S. 1015-1025 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The living stereospecific polymerization of methylthiirane initiated by a chiral cadmium compound was run in different solvents. The general features of the mechanism of stereoregulation are the same as in bulk. In heptane and in heptane/propylene carbonate mixtures, the stereospecificity of the reaction does not depend on monomer concentration and on the dielectric constant ε of the medium. This independence of stereospecificity is in agreement with the absence of a variation of the complexation constant between a model cadmium derivative and the monomer with the variation of ε in a large range. The enantioasymmetric process depends on the molecular weight of the chain bearing the active sites. A change from diastereoisomeric to enantiomeric forms of active sites occurs for molecular weights around 50000. The enantioasymmetric constant depends on the nature of the medium and we observed a Born law for the dependence of the enantioasymmetric constant versus reciprocal dielectric constant: log kR ∝ 1/ε. This effect can be explained by a variation of the reactivities of the two types of active sites and occurs without a change in their relative amounts.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1993.021940324
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  • 4
    Electronic Resource
    Electronic Resource
    Stereospecific polymerization of methylthiirane in homogeneous phase, 1. Oligomerization step and change in stereocontrol with molecular weight (1984)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 185 (1984), S. 1317-1326 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The polymerization of methylthiirane in homogeneous phase initiated by bis(isopropylcysteinato)cadmium is a living process. For low conversions, oligomers (essentially heptamers and octamers) are formed, apparently using one valency of cadmium, the main propagation taking place by using the other one. However, the size of the oligomers may still grow for higher conversions. The mechanism of the oligomer formation depends on the temperature. A “normal” insertion of the monomer is observed at -23°C, whereas at 20°C a disulfide bond is formed. The preferential choice of a different enantiomer in the main propagation reaction may depend on the presence of a particular type of oligomer, in the vicinity of cadmium, linked to the cysteine group. However, stereospecificity (stereoselection and stereoelection) appears only with molecular weights higher than 6000 and also depends on the temperature of propagation: with decreasing temperature, the stereoregularity increases and the stereoelection can be inverted (for a definite oligomer structure).
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1984.021850705
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  • 5
    Electronic Resource
    Electronic Resource
    Stereospecific polymerization of methylthiirane in homogeneous phase, 3.Part 2: cf. ref. 6 Study of the enantioasymmetric process (1993)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 194 (1993), S. 1003-1014 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Enantioasymmetry was studied for polymerizations of methylthiirane initiated by bis(isopropyl-S-cysteinato)cadmium and run in bulk. The ratio of rates of consumption of the two antipodes is independent of their concentrations. The enantioasymmetric constant kR, measuring the preferential choice of the R-antipode, is depending on both the relative number of the two types of active sites and on their reactivities. An effect on enantioasymmetry of the molecular weight of the growing chains bearing the active sites, is occurring with two distinct stages: The first one is observed, with an enantioasymmetric constant kR = 1,5, from the appearance of stereospecificity up to molecular weights of 35000 (for the main chain) and the second one with kR = 1,07 for molecular weights higher than 35000. In the first stage, the cysteinato end group of the oligomer chain remains linked to cadmium (by cadmium-nitrogen complexation) and the two active sites are diastereoisomers having different reactivities. In the second stage, the macrocyclic oligomer becomes too large and cadmium-nitrogen interaction is suppressed. The active sites are now enantiomers having the same reactivity. In this case, enantioasymmetry depends only on the unbalance between the amounts of the two types of active sites. The maximum size the macrocyclic oligomer can reach depends on the initiator concentration.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1993.021940323
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  • 6
    Electronic Resource
    Electronic Resource
    Stereospecific polymerization of methylthiirane in homogeneous phase, 2.Part 1: cf. ref.3. Mechanism of stereoregulation (1992)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 193 (1992), S. 1709-1721 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In the living polymerization of methylthiirane initiated with bis(isopropyl-(S)-cysteinato)-cadmium, stereospecificity depends on temperature of propagation, on initiator concentration and also on the length of the growing polymer chain. The kinetics of stereospecific and non-stereospecific processes are described. In both cases, the order with respect to monomer is equal to zero and that with respect to initiator is one-half. The stereospecific propagation is proposed to involve cadmium thiolates associated as “dimeric species” and coordinated by both the monomer and by an oligomeric or polymeric chain.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1992.021930714
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  • 7
    Electronic Resource
    Electronic Resource
    Role of cocatalysts in polymerizations initiated with benzyl derivatives of transition metals, 2Part 1: cf.1.. Polymerization of styrene (1983)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 184 (1983), S. 1397-1406 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymerization of styrene in toluene solution at 50°C was found not to be initiated with sufficiently pure tetrabenzylzirconium or -titanium. However, a cocatalytic effect of water was observed with a maximum rate for a mole ratio H2O/Mt (Mt = Zr or Ti) close to 0,1. No activities were observed for the hypothetical compounds (C6H5CH2)3Mt - O - Mt(CH2C6H5)3. This cocatalytic effect was also observed with tribenzylchlorozirconium (1), tribenzylzirconiooxytriphenylsilane (2), or 6,6-dibenzyl-2,2,4,4-tetramethyl-1,3,5-trioxa-2,4-disila-6-zirconacyclohexane (3). Styrene polymerizations were also initiated by supported catalysts obtained by reaction of Zr(CH2C6H5)4 with aluminium oxide or silicium oxide pre-dried at various temperatures. The activities of such systems were equal or slightly lower than those obtained with the system Zr(CH2C6H5)4/H2O (mole ratio 10 : 1). The resulting polystyrenes have very high molecular weights with very broad distribution. Copolymerization experiments with methyl methacrylate gave as main product a copolymer containing only 4% of monomeric units of styrene. A discussion of all results led to the conclusion that the main polymerization involves an anionic-type propagation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1983.021840708
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  • 8
    Electronic Resource
    Electronic Resource
    Preparation and polymerization of racemic and optically active tert-butyl thiiraneDedicated to Professor Dr. CH. SADRON on the occasion of his 70th birthday (1972)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 156 (1972), S. 55-64 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Darstellung und die Polymerisation von tert-Butyl-äthylensulfid werden beschrieben. Das racemische Monomere wurde durch Umsetzung von tert-Butyl-äthylenoxid mit Kaliumrhodanid in wäßriger Lösung erhalten. Das linksdrehende Enantiomere wurde aus R(-)-3.3-Dimethyl-butandiol-(1.2) über das cyclische Carbonat als Zwischenprodukt synthetisiert. Die Polymerisation des racemischen Monomeren mit Koordinationskatalysatoren ergibt kristalline, lösliche Produkte hohen Molekulargewichts und von hohem Schmelzpunkt (nahe bei 205°C). Kristalline, lösliche Polymere mit hohem Molekulargewicht, jedoch mit tieferen Schmelzpunkten (nahe bei 160°C) konnten auch mit dem linksdrehenden Enantiomeren entweder durch koordinierte oder durch anionische Initiierung erhalten werden. Diese Polymeren besitzen hohe optische Drehungszahlen, welche in allen verwendeten Lösungsmitteln positives Vorzeichen besitzen. NMR-Messungen zeigen, daß racemische und optisch aktive kristalline Polymere die gleiche isotaktische Struktur haben. Wie die Röntgendiagramme zeigen, sind die Unterschiede in den Schmelzpunkten auf die Existenz verschiedener kristalliner Modifikationen zurückzuführen. Diese Resultate zeigen einen starken Unterschied zu den bei der Polymerisation von Methyläthylensulfid gewonnenen Ergebnissen.
    Notes: Preparation and polymerization of tert-butyl thiirane are described. The racemic monomer was obtained by reaction in aqueous solution of tert-butyl oxirane and potassium thiocyanate. The levorotatory enantiomer was synthesized from R(-) 3.3-dimethyl 1.2-butane diol passing through the intermediate of the cyclic carbonate. Polymerization of the racemic monomer with coordinate type initiators give crystalline, soluble products of high molecular weights and high melting points (close to 205°C). Crystalline, soluble, high molecular weight polymers but of lower melting points (close to 160°C) could also be obtained with the levorotatory enantiomer, either by coordiante or purely anionic initiation. These polymers have high optical activities of positive sign in all the solvents used. NMR measurements show that racemic and optically active crystalline polymers have the same isotactic structure. The differences in melting point and X-ray diagrams show the existence of several crystalline modifications. These results indicate a strong difference in the behaviour of tert-butyl thiirane as compared to methyl thiirane.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1972.021560106
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis of an amphiphilic triarm star copolymer based on polystyrene, poly(ethylene oxide) and poly(ε-caprolactone) (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 18 (1997), S. 343-351 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The synthesis of an amphiphilic triarm star copolymer based on polystyrene, poly(ethylene oxide) and poly(ε-caprolactone) block has been achieved by a novel strategy which consists in the preparation of a diblock copolymer, polystyrene-block-poly(ethylene oxide), having a protected anionic initiator group at the junction of the two blocks. After deprotection, this function is activated by a coloured and weakly basic carbanion. The generated alcoholate initiates the ε-caprolactone anionic polymerization.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1997.030180411
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  • 10
    Electronic Resource
    Electronic Resource
    Stereospecific polymerization of methylthiirane in homogeneous phase, 5Part 4: cf. ref.8.. Study of the interconversion between active sites (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 4069-4082 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The enantioasymmetry of polymerization reactions of racemic methylthiirane in bulk are studied, initiation being made using racemic or optically active seeds of molar weight equal to 40000, synthesized in bulk from bis(isopropyl-S-cysteinato)cadmium. In these conditions, active sites are enantiomers and the enantioasymmetric constant kR, measuring the preferential choice of the R antipode, is depending only on the relative number of the two types of active sites. We have observed an interconversion between the enantiomeric active sites CR* and CS*. The ratio [CR*]/[CS*] is only varying with conversion and reaches a limiting value that depends on cadmium concentration. For low cadmium concentrations, ([CR*]/[CS*])lim = 1.00, showing a complete racemization of the enantiomeric active sites, while for higher cadmium concentrations, ([CR*]/[CS*])lim = 1.07 ± 0.03. This value of 1.07 can be attributed to the presence of aggregation of dimeric species which create a chiral neighbourhood around cadmium atoms. Diastereoisomeric active sites present when active sites are born by chains of lower molar weights seem also to interconvert. The interconversion between active sites implies the presence of stereoblocks in the main chain.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1995.021961216
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