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  • 1980-1984  (4)
  • 1984  (3)
  • 1981  (1)
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  • 1980-1984  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Ion-trapping in cationic polymerization, 2.Part 1: cf.1. Relative rates of trapping and relative chemical shifts for structurally differing phosphines as trapping agentsPresented in part at the IUPAC Macromolecular Symposium in Mainz, September 1979. (1981)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 182 (1981), S. 1735-1742 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of ethyl trifluoromethanesulfonate with phosphines to form phosphonium salts was used as a model reaction for the “trapping” of the various propagating species by phosphines in the polymerization of THF and other cyclic ethers. In dichloromethane at 25°C, the values of the bimolecular rate constant ktr were determined for various phosphines. For (C6H5)3P:5.10-3 mol-1.l.s-1, for (C6H5)(CH3)2P:0,22 mol-1.l.s-1, for (C6H5)(n-C3H7)-(CH3)P:0,13 mol-1.l.s-1, and for (n-C4H9)3P: 1,3 mol-1.l.s-1. It was found that the ratio ktr/ka (ka is the rate constant of the ethylation of THF by ethyl trifluoromethanesulfonate) changes from 40 for triphenylphosphine to 104 for tributylphosphine. Differences of chemical shifts, measured for various quaternary phosphonium cations differing in one substituent, were observed for ions with various substituents (e.g. based on parent methylpropylphenylphosphine).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1981.021820614
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Cationic polymerization of 1-azabicyclo[4.2.0]octane, 1 alkylation (1984)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 185 (1984), S. 37-49 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rate constants of the reaction of 1-azabicyclo[4.2.0]octane (1) with different alkyl esters or halides were measured using 1H NMR and UV spectroscopy as well as conductometric methods. The reactivities of the alkylating agents were found to decrease with increasing nucleophilicity of the derived anions (CF3SO⊖3 〉 I⊖ 〉 Br⊖ 〉 picryl⊖ 〉 Cl⊖). Reactivities of all ethyl derivatives, except ethyl chloride, are higher than the reactivity of the 1-alkyl-1-azoniabicyclo[4.2.0]octane cation (2), which means that for these compounds the rate constant of initiation is higher than that of propagation. The reactions proceed much slower in methanol than in nitrobenzene due to the strong donor-acceptor interactions between methanol and 1. Attempts to observe covalent active centers directly by NMR spectroscopy in the polymerization mixture or to detect them kinetically, were unsuccessfull. The reactivity of ethyl triflate, modelling the hypothetical active center, was found to be 2.104 times higher than the reactivity of ions 2. This is ascribed to the high strength of the bond in the cation 2, not sufficiently compensated by the strain of the four-membered ring.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1984.021850105
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Cationic polymerization of 1-azabicyclo[4.2.0]octane, 2.Part 1: cf. 10. Reactivities of ions and ion-pairs (1984)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 185 (1984), S. 51-66 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The cationic ring-opening polymerization of 1-azabicyclo[4.2.0]octane (1) was studied with initiators providing small and large anions, namely F⊖, Br⊖, I⊖, picryl(Pic⊖), CF3SO3⊖. In nitrobenzene as solvent the macroions and macroion-pairs, independently of the anion size, propagate with the same rate constant kp+ = kp± = 7,0 · 10-3 mol-1 · l · S-1 at 35°C ( Δ HP≠ = 55 ± 5kj· mol-1, Δ SP≠ = 105 ± 11 j · mol-1 · K-1). This result strongly indicates that it is not the large size of anoins which is exclusively responsible for the equality kP+ = kP±. The structure of the onium ions, their strong solvation, and the resulting weak interactions with anions are primarily responsible for the observed equalities. In methanol as solvent polymerization proceeds 30 times slowlier than in nitrobenzene and ion-pairs are more reactive by 40% than ions, in agreement with Enikolopyan's findings.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1984.021850106
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Cationic polymerization of 1,4,6-trioxaspiro [4,4]-nonane (1984)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 22 (1984), S. 29-40 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cationic polymerization of 1,4,6-trioxaspiro [4,4]-nonane (1) with (CH3)3O+SbF6-(2) and CH3OSO2CF3(3) initiators has been investigated. Although the observed rates of initiation and propagation are relatively slow, they consist of rapid reversible elementary reactions. In 1H-NMR spectra, a broadening of the monomer signal was observed, indicating a fast exchange between “free” monomer and monomer engaged in the active species. The variety of orthoester bonds were observed in the polymer formed at the early stages of monomer conversion. The final polymer has, however, structure of a linear poly(ester-ether) including two subsequent ester or ether linkages. To account for these new facts, the mechanism of polymerization was proposed, consisting of a rapid reversible opening of one of the rings in the monomer molecule involved in the growing species, followed by the slower opening of the second ring with formation of the ester linkages. It appears that the rings originally present in the chains rearrange into the linear units intramolecularly.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1984.170220103
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    Paper (German National Licenses)
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