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  • 1
    Electronic Resource
    Electronic Resource
    Über die stereoelektronischen Bedingungen der 1,2-Umlagerungen bei Vinylkationen (1984)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 117 (1984), S. 2815-2824 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: On the Stereoelectronic Requirements of 1,2-Rearrangements of Vinyl CationsThe triflates 8, 9, 12, 17, 19, and 23 have been synthesized to investigate their solvolysis products in absol. 2,2,2-trifluoroethanol (TFE) (Table 1). The kinetics of the solvolysis in 50% ethanol have been measured as well. The rate constants give a straight correlation line when we apply an approximate Taft's equation, from which we deduce that the solvolyses take place by a kc mechanism; one exception is 12, as it reacts with S-O bond cleavage. We also deduce that the value of ρ* does not depend on steric factors. Relations between structure and rearrangement of vinyl cations are discussed. Mechanisms for the formation of reaction products are proposed.
    Notes: Die Triflate 8, 9, 12, 17, 19 und 23 wurden synthetisiert, um die Produkte ihrer Solvolyse in absol. 2,2,2-Trifluorethanol (TFE) zu untersuchen (Tab. 1). Auch die Kinetik der Solvolysen in 50proz. Ethanol wurde bestimmt (Tab. 2). Die Solvolysegeschwindigkeiten ergeben eine Korrelationsgerade bei einer vereinfachten Taftschen Darstellung, woraus abgeleitet wird, daß die Solvolysen nach einem kc-Mechanismus erfolgen; eine Ausnahme ist 12, das durch S-O-Spaltung solvolysiert. Wir schließen daraus, daß ρ* von sterischen Effekten unabhängig ist. Es werden Beziehungen zwischen Struktur und Umlagerung bei Vinylkationen diskutiert und Mechanismen für die Bildung der Reaktionsprodukte vorgeschlagen.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19841170904
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  • 2
    Electronic Resource
    Electronic Resource
    Copolymerization of β-pinene with styrene oxide and N-vinylpyrrolidone (1982)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 20 (1982), S. 1279-1285 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The copolymerization of β-pinene with styrene oxide (SO) and β-pinene with N-vinylpyrrolidone (VP) was investigated by using SnCl4 in dichloromethane diluent at low temperature. Monomer reactivity ratios were evaluated for both copolymers at -80°C; these are r1(SO) = 2.979 and r2(β-pinene) = 0.002 and r1(VP) = 0.096 and r2(β-pinene) = 0.294.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1982.170200511
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of tacticity on thermal degradation of PVC. V. Relation between the nature of labile conformations and the polyene distribution in the degraded polymer (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 28 (1983), S. 33-43 
    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: Four poly(vinyl chloride) (PVC) samples, 1, 2, 3, and 4, were prepared in bulk using 2,2′-azodiisobutyronitrile at 90°C and 60°C and the same initiator together with UV irradiation at 0°C and -50°C, respectively. Fractions were obtained from samples 2,3, and 4 by extracting with acetone, sample 1 being completely soluble in this solvent. The whole PVC's as well as their acetone soluble and insoluble fractions, were characterized by determining the intrinsic viscosity, the osmometric molecular weight, and the tacticity; then they were thermally degraded up to conversion of 0.3% in powder state. The values of degradation rate for both the insoluble fractions and the whole PVC's were in agreement with some prior results on the influence of syndiotactic sequences on propagation step. The soluble fractions proved to be very unstable in comparison with the insoluble, which, despite the lower molecular weight of the former, seems to obey their higher content of isotactic conformations. The fine polyene distribution in the degraded polymers was carried out by UV-visible spectroscopy. The results reveal the occurrence of two different polyene distributions, and allow for the peculiar one of the soluble fractions to be related to polyenes consisting of two sequences of trans conjugated double bonds separated by a single cis double bond. The results clearly shows that there are two mechanisms for initiation of the PVC degradation, depending on whether it occurs by random unstable structures or by the normal GTTG isotactic or TTTG heterotactic triads. Moreover, these two initiation processes are proved to give rise to different types of polyenes, which accounts for the occurrence of two unlike mechanisms of propagation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1983.070280104
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of tacticity on the thermal degradation of PVC. VI. New advances in the degradation process through the behavior of modified PVC samples (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 29 (1984), S. 1735-1741 
    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: Three PVC samples having different tacticities, as well as the products resulting from their reaction with sodium thiophenate, which was previously found to occur selectively by some definite isotactic conformations, were degraded at 180°C in solid state up to 0.3%. In agreement with prior works, the stability of the substituted polymers was shown to be higher as the substitution extent increased up to a definite value, which depends on the overall isotactic content of the starting materials. On the other hand, the found changes in polyene distribution for the degraded samples with the substitution extent, as followed by UV-visible spectroscopy, demonstrate that the specific bands at 393, 416, and 437 nm, which are known to be characteristic for the most unstable PVCs, arise from the lability of some chlorine atoms located at GTTG′ (or TTTG) conformations, as prior results suggested. On the basis of the so-obtained correlation between the content of some isotactic triads (especially the GTTG′) and both the thermal instability and the formation of the above-indicated specific polyenes, new advances in the degradation mechanism are proposed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1984.070290526
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  • 5
    Electronic Resource
    Electronic Resource
    Anionic and radical polymerization of p-triphenyl- and p-tributylgermyl-styrenes (1983)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 184 (1983), S. 961-967 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Anionic polymerization of p-triphenylgermylstyrene (1a) and p-tributylgermylstyrene (1b) were investigated under high vacuum conditions (≈10-6 mbar). Both 1a and 1b were readily polymerized with sodium naphthalide, potassium naphthalide, or α-methylstyrylsodium oligomers to form “living polymers”. The addition of α-methylstyrene to these living systems gave the triblock copolymer, poly(α-methylstyrene-b-p-triphenylgermylstyrene-b-α-methylstyrene). Both monomers were also polymerized radically with AIBN as initiator. Some physical properties of the resulting polymers were examined.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1983.021840508
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  • 6
    Electronic Resource
    Electronic Resource
    Polyene sequence distribution in modified poly(vinyl chloride) after thermal degradation (1984)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 185 (1984), S. 1277-1284 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The products resulting from the reaction of PVC with sodium benzenethiolate were degraded to 0,3% at 180°C in the solid state and at 160°C in solution in trichlorobenzene. The polyene distribution of the polymers after degradation was studied by both UV-visible and resonance Raman spectroscopies, as a function of the degree of substitution. The results show that there are two types of behaviour: that of the PVC sample prior to the substitution reaction together with the samples modified up to a definite degree of substitution which depends on the starting isotactic content, and that of samples with higher degrees of substitution. The former group exhibits not only a steady improvement in thermal stability but also a preferential formation of polyenes of 7 - 9 double bonds whose concentration decreases with increasing degree of substitution. Conversely, for the second group of samples the thermal stability decreases with the degree of substitution and no specific absorption bands are observed. On the basis of earlier work on the selective substitution of the isotactic GTTG and heterotactic TTTG triads during the first stage of the reaction, the present results show that the bands at 393, 416, and 437 nm are related to specific polyenes which result from initiation by the above quoted conformations in PVC, a conclusion for which confirmatory evidence was obtained by resonance Raman spectroscopic examination of the samples. There is, therefore, clear evidence for the occurrence of two distinct degradation mechanisms, one involving initiation by the unstable triad conformations and the other via random initiation at stable and normal structures. To this may be added the initiation by defect structures, which have been extensively documented in the literature.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1984.021850701
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  • 7
    Electronic Resource
    Electronic Resource
    The cationic polymerization of 2-alkenylfurans, 2Part 1: cf.5. A side reaction leading to polyunsaturated products (1982)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 183 (1982), S. 2399-2413 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A spectroscopic and conductimetric study of the cationic polymerization of 2-vinylfuran (1) and 2-methyl-5-venylfuran (2) showed the existence of an important side reaction originating from a hydride-ion shift from an unsaturated polymer molecule to an active species. The resulting allylic carbocation, in equilibrium with a doubly unsaturated polymer molecule, can react further and the repetition of the mechanism on progressively more conjugated species leads to the formation of a series of highly charge-delocalized carbenium ions absorbing throughout the visible region of the spectrum (and giving high electrical conductivity) and of neutral polyconjugated polymer molecules. Since the hydride-ion abstraction occurs from the tertiary carbon atom of the vinylic chain, vinylidene polymers of monomers such as 2-isopropenylfuran (3) and 2-isopropenyl-5-methylfuran (4) are not susceptible to it. Indeed, their cationic polymerization proceeds without colour formation and conductivity increase.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1982.021831010
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  • 8
    Electronic Resource
    Electronic Resource
    The cationic polymerisation of 2-alkenylfurans, 3Part 2: cf. 2.. Spectroscopic study of the alkylation as important side reaction leading to branched products (1983)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 184 (1983), S. 1189-1211 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A spectroscopic (UV, IR, 1H NMR) study of the cationic polymerisation of 2-vinylfuran (1a) and 2-isopropenylfuran (2a) showed the existence of an important alkylation reaction at C5 which competes with normal propagation. The extent of this competition depends on the monomer used and the polymerisation temperature. A comparison of the spectra of standard polymers (prepared by radical or stereospecific polymerisation) with those of polymers obtained by cationic initiation allowed to assess the extent of alkylation and its regiospecificity at C5 2-Methyl-5-vinylfuran (1b) and 2-methyl-5-isopropenylfuran (2b) were found to undergo cationic polymerisation without any interference from alkylation reactions. Reactions between these four monomers and 2-methylfuran in the presence of typical acidic catalysts gave very high yields of alkylated products and no polymerisation, thus confirming the importance of this electrophilic reaction and its possible application to synthetic uses.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1983.021840608
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  • 9
    Electronic Resource
    Electronic Resource
    Dimensions of short, rodlike macromolecules from translational and rotational diffusion coefficients. Study of the gramicidin dimer (1984)
    New York : Wiley-Blackwell
    Biopolymers 23 (1984), S. 611-615 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360230402
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  • 10
    Electronic Resource
    Electronic Resource
    Vinylkationen, 36. Solvolyse von Cycloalkylidenmethyl- und 1-Cyclopenten-1-yl-triflaten (1982)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 115 (1982), S. 772-782 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Vinyl Cations, 36. Solvolysis of Cycloalkylidenemethyl and 1-Cyclopenten-1-yl TriflatesCyclohexlidenemethyl triflate (2), cyclobutylidenemethyl triflate (5), 1-cyclopenten-1-yl triflate (7), bicyclo [3.1.0]hex-2-en-2-yl triflate (9), 1-cyclobutylideneethyl triflate (19), and 2-methyl-1-cyclopenten-1-yl triflate (29) were solvolyzed in solvents of various ionizing power and nucleophilicity and the solvolysis products were identified. The cyclobutylidenealkyl triflates solvolyze via a vinyl cation mechanism involving ion pairs with rearrangement to cyclopentene and cyclopentanone compounds. The 1-cyclopenten-1-yl triflates do not produce vinyl cation intermediates but give only the corresponding ketones via an O—S bond cleavage of the triflate group.
    Notes: Cyclohexylidenmethyl-triflat (2), Cyclobutylidenmethyl-triflat (5), 1-Cyclopenten-1-yl-triflat (7), Bicyclo[3.1.0]hex-2-en-2-yl-triflat (9), 1-Cyclobutylidenethyl-triflat (19) und 2-Methyl-1-cyclopenten-1-yl-triflat (29) wurden in Lösungsmitteln verschiedener Ionisierungsstärke und Nucleophilie solvolysiert und die Solvolyseprodukte aufgeklärt. Die Cyclobutylidenalkyl-triflate solvolysieren über Ionenpaarmechanismen (Vinylkationen) unter Umlagerung zu Cyclopenten- und Cyclopentanon-Derivaten. Die 1-Cyclopenten-1-yl-triflate reagieren nicht über Vinylkationen als Zwischenstufe, sondern unter O—S-Spaltung zu den entsprechenden Ketonen.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19821150238
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