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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Local chain configuration dependence of the mechanisms of analogous reactions of PVC. I. A conclusive study of the microstructure evolution in SN2 nucleophilic substitution (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 2387-2397 
    Details
    ISSN: 0887-624X
    Keywords: poly(vinyl chloride) ; nucleophilic substitution ; stereospecific mechanisms ; solvent influence ; microstructural sensitivity ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nucleophilic substitution in poly(vinyl chloride) (PVC) with sodium benzenethiolate has been studied in two kinds of solvent differing in the molecular structure in the vicinity of the carbonyl group. From the evolution of the content of isotactic (mm), heterotactic (mr), and syndiotactic (rr) triads; and of mmmm, mmmr and rmmr isotactic pentads, in the unmodified parts of the polymer, as followed by 13C-NMR, it is unambiguously inferred that any chlorine but the central one of either the isotactic triad at mmr tetrads or the heterotactic triad at rmrr pentads is unreactive. Only a small fraction of mmr tetrads reacts occasionally by the central chlorine of its mr triad instead of the mm. Of those structures, the mmr, especially when located at the end of long isotactic sequences, proves to be highly reactive compared to the rmrr structure. By comparing quantitatively the microstructural changes with degree of substitution and taking into account that the reaction is of SN2 type, the mechanisms of substitution through the three foregoing reactive chlorines have been stated. They are found to be independent of the type of solvent and to account for all the changes in triad and pentad content as experimentally found. Instead, the solvent dependence of the ratio between the mmr- and rmrr-based processes of substitution is such that the depletion of mmr compared to that of rmrr structure may be controlled. The conformational sensitivity of this behavior is discussed on the basis of side work in our laboratory. As a whole, the results of the present work provide some original concepts as to the role of the tacticity dependent microstructure and the related local conformations in the chemical reactions of PVC. © 1996 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Local chain configuration dependence of the mechanisms of analogous reactions of PVC. II. A further evidence through the changes in conformationally sensitive FTIR bands with degree of nucleophilic substitution (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 2563-2574 
    Details
    ISSN: 0887-624X
    Keywords: poly(vinyl chloride) ; stereoselective substitution ; FTIR vibration modes ; local configurational mechanisms ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The evolution of the ν C (SINGLE BOND) Cl bands of the infrared spectrum of a Bernoullian though slightly isotactic poly(vinyl chloride) (PVC), with both the degree of SN2 substitution reaction with sodium benzenethiolate, as studied earlier, and the increase of the nucleophile infrared bands, has been studied by FTIR spectroscopy. In a parallel way, the changes in the same bands, in particular those at 615 and 637 cm-1, presumably induced by SN2 substitution, have been estimated, theoretically, by comparing the sequential order and the number of the distinct conformationally sensitive vibration modes of C(SINGLE BOND)Cl bond, prior and after substitution, for a series of polymer sequences containing the reactive sites, namely the isotactic mmr tetrad and the heterotactic rmrr pentad, according to earlier work.The experimental behaviour of the νC(SINGLE BOND)Cl bands is found to be in close agreement with the theoretical expectations, thereby allowing two main conclusions to be drawn: (i) during the early stage going up to conversions of 10-12%, the reaction proceeds in a nearly exclusive manner, by the mmr and rmrr terminal of long isotactic and syndiotactic sequences, respectively; and (ii) any reaction event throughout the substitution process proves to be highly dependent upon the local environment in which each of the foregoing reactive structures finds itself. In summary, the local configurational nature of the mechanisms of analogous reactions of polymers is strongly suggested on the grounds of the results given herein. © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    The influence of the tacticity on thermal degradation of PVC. II. New results obtained with fractionated polymers (1975)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 45 (1975), S. 177-184 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Bei 40, 0 und -50°C hergestellte PVC-Proben wurden nach verschiedenen Methoden fraktioniert. Die Fraktionen wurden durch Viskositätsmessungen und IR-Spektroskopie charakterisiert. Der thermische Abbau der Fraktionen wurde bei 175, 180 und 185°C durch fortlaufende Messung des abgespaltenen Chlorwasserstoffs in einem Leitfähigkeitsapparat untersucht. Die kinetischen Ergebnisse und die Spektren der Proben zeigen, daß die syndiotaktischen Sequenzen die Ursache für den schnellen Abbau sind und daß dabei lange Polyensequenzen entstehen, wie schon früher bei unfraktionierten Polymeren ermittelt wurde.
    Notes: PVC samples prepared in bulk at 40, 0, and -50°C were fractionated by different methods. The samples were characterized by viscosimetric measurements and by IR spectroscopy in order to determine the tacticity. The thermal degradation of the samples was studied at 175, 180, and 185°C by means of continuous measuring of the evolved HCl in a conductivity apparatus. From the kinetic results and the UV-visible spectra recorded on equally degraded samples follows that syndiotactic sequences give rise to high degradation rates as well as to long polyene sequences in agreement with results previously obtained with unfractionated polymers.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1975.050450113
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of the molecular weight on thermal degradation of fractionated PVC (1975)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 46 (1975), S. 81-87 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Ein technisches PVC und eine andere in Substanz bei 40°C hergestellte Probe wurden nach der Lösungsmethode mit Methanol-Cyclohexanon-Gemischen fraktioniert. Beide Polymere geben Fraktionen mit gleicher Taktizität, aber verschiedenen Molekulargewichten. Der thermische Abbau wurde bei 175, 180 und 185°C durch fortlaufende Bestimmung des abgespaltenen HCl in einem Leitfähigkeitsapparat untersucht. Je niedriger das Molekulargewicht ist, desto größer ist die Abbaugeschwindigkeit; dies gilt aber nur für Polymere mit Molekulargewichten bis etwa 60 000 oder 90 000; oberhalb dieser Werte ist die Abbaugeschwindigkeit vom Molekulargewicht unabhängig. Die Spektren der Proben mit dem gleichen Abbauumsatz zeigen, daß die Verteilung der Polyensequenzen gleich ist und daher nicht vom Molekulargewicht beeinflußt wird.
    Notes: A commercial PVC and another one prepared in bulk at 40°C were fractionated by means of fractional solution method using cyclohexanone-methanol mixtures. Both fractionations resulted in two sets of fractions. Their thermal degradation at 175, 180 and 185°C was followed by means of a conductivity cell which allows a continuous titration of the evolved HCl. The results showed that the lower the molecular weight the higher the degradation rate was; nevertheless, this relationship is only valid up to molecular weights of 60 000 to 90 000, from which the degradation rate appeared to be independent on the molecular weight. The UV-visible spectra of the degraded polymers suggest a similar polyene sequence distribution for all the fractions which accounts for a similar mechanism of degradation in contrast to what happens to fractions with different tacticity.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1975.050460108
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  • 6
    Electronic Resource
    Electronic Resource
    The influence of the tacticity on thermal degradation of PVC. III. Verification by ozonization of degraded samples (1979)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 75 (1979), S. 215-222 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Mit abgebauten PVC-Proben verschiedener Taktizitäten wurden zwei Reihen Ozonolysereaktionen mit 1 und 24 h durchgeführt. Bei der Ozonolyse wurde die Verteilug der Polyensequenzlängen durch UV-Vis-Spektroskopie verfolgt. Die Kettenspaltungszahl der analysierten Proben wurde durch Bestimmung des Molekulargewichtes vor und nach der Ozonolyse berechnet.Die beobachtete Zunahme der kürzeren Polyensequenzen im Vergleich zu längeren Polyensequenzen bei der Ozonolyserektion hängt von den syndiotaktischen Sequenzen ab. Es wurde andererseits gefunden, daß bei PVC die Zahl der Kettenspaltungen nach der vollständigen Ozonolyse um so kleiner ist, je größer der Anteil von taktischen Sequenzen ist.
    Notes: Two sets of ozonization reactions, for 1 h and 24 h respectively, have been carried out at -20°C on degraded samples of PVC having different contents of tactic sequences. The evolution of the polyene sequences distribution with the ozonization was followed by UV-Visible spectroscopy. The number of chain scissions of ozonized samples was calculated from the number average molecular weight measurements before and after ozonization.The observed increase of short polyenes relative to the long polyenes with ozonization was found to depend markedly on the content of syndiotactic sequences. On the other hand, the number of chain scissions after total ozonization was found to be the higher the lower the content of tactic sequences in PVC samples is.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1979.050750116
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  • 7
    Electronic Resource
    Electronic Resource
    A comprehensive approach to the stereochemical and physical factors in nucleophilic substitution on PVC in the melt (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 38 (1989), S. 1685-1698 
    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 nucleophilic substitution reactin of poly(vinyl chloride) (PVC) with sodium benzenethiolate (NaBT) has been studied in the melt with the aim of determining whether a conformational mechanism is applicable under conditions that would apply in the polymer processing. The evolution of unreacted syndio, hetero, and isotactic triads content, and of the apparent molecular weight has been followed by 13C-NMR and GPC, respectively. The kinetic behavior was defined by choosing appropriate mixing conditions of temperature, shear stress, load, and amount of plasticizer. In all cases the kinetic curves attain a plateau after a rather fast reaction period has elapsed. The conversion at the plateau, that is, the reaction efficiency, proved to depend linearly on the amount of nucleophile and is hardly influenced by the mixing conditions for a given stoichiometric composition. The mixing conditions have been found to affect markedly the kinetics but to be quite inoperative on the evolution of both the content of unreacted tactic triads and the apparent molecular weight with degree of conversion. The results are discussed by taking into consideration those previously obtained in solution.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1989.070380909
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  • 8
    Electronic Resource
    Electronic Resource
    Sub-Tg molecular motions in glassy poly(vinyl chloride). Influence of the nucleophilic substitution (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 871-880 
    Details
    ISSN: 0887-6266
    Keywords: modified poly(vinyl chloride) ; dielectric ; relaxation ; stretched exponential law ; coupling model ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dielectric local molecular motions in the glass transition region of poly(vinyl chloride) (PVC) have been investigated by means of the isothermal depolarization currents technique. Attention is paid to the influence of the modification of the polymer by the substitution of chlorine atoms of PVC chain by the benzenethiolate group. The results are well described by stretched exponential laws. According to the Ngai's coupling model, the coupling between moving units as well as the activation energy responsible for the motions occurring at primitive level have been calculated for each sample at each temperature. All these parameters are noticeably altered by the modification of PVC. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090320510
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Chemical modification of poly(vinyl chloride): A conclusive study of the influence of tacticity (1985)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 23 (1985), S. 1077-1087 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three samples, A, B and C, of poly(vinyl chloride) (PVC) were prepared at 90, 60, and 0°C, respectively, to give them different isotactic content measured by 13C-NMR spectroscopy. A kinetic study of the nucleophilic substitution with sodium thiophenate, carried out for the three samples, showed that even at temperatures as high as 60°C a fraction of the units remain unreactive and that the extent of this fraction depends on the syndiotactic content of the polymer. This was also supported by a comparison of the behavior of samples B and C in substitution experiments at 5 and 60°C. In contrast the substitution experiments at -30°C demonstrated that, as suggested, a small fraction of extremely reactive units exists in PVC, the content of which is higher as the isotactic content of the polymer increases. In this connection, and even though a slight contribution of some defect structures cannot be ruled out, a 13C-NMR analysis of sample B after modification at 40°C to various degrees demonstrates that the reactivity of the isotactic triads is high in relation to the heterotactic. On the basis of the results obtained and the possible conformations in PVC the substitution mechanism is related to the occurrence of isotactic TT conformations. The results, as discussed in terms of the various ways in which isotactic TT conformations appear open new prospects in the field of PVC chemical modification and stabilization mechanisms.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1985.170230412
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