Experimental and Theoretical Evaluation of the Reactions Leading to Formation of Internal Double Bonds in Suspension PVC
| Autor: | Kim F. D. Pauwels, Arend Jan Schouten, Michela Agostini, Michelle L. Coote, Jindra Purmova, Maarten Bruinsma, Eltio J. Vorenkamp |
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| Přispěvatelé: | Polymers at Surfaces and Interfaces, Zernike Institute for Advanced Materials |
| Rok vydání: | 2008 |
| Předmět: |
Reaction mechanism
TERTIARY CHLORINE Polymers and Plastics Double bond Radical polymerization HYDROGEN ABSTRACTION REACTIONS POLY(VINYL CHLORIDE) THERMAL-STABILITY ANOMALOUS STRUCTURES Hydrogen atom abstraction Photochemistry Vinyl chloride Inorganic Chemistry chemistry.chemical_compound POLYVINYL-CHLORIDE) Materials Chemistry C-13 NMR ANALYSIS Organic chemistry chemistry.chemical_classification VINYL-CHLORIDE POLYMERIZATION FREE-RADICAL POLYMERIZATION Organic Chemistry Polyvinyl chloride BRANCH STRUCTURES Monomer chemistry Intramolecular force |
| Zdroj: | Macromolecules, 41(15), 5527-5539. AMER CHEMICAL SOC |
| ISSN: | 1520-5835 0024-9297 |
| DOI: | 10.1021/ma800583k |
| Popis: | The number of internal double bonds in poly(vinyl chloride) (PVC) samples was studied as a function of molecular weight at various monomer conversions. These defect structures were found to exhibit end-group-like characteristics: their concentration per chain was largely constant as a function of molecular weight. This tendency was independent of the degree of conversion. An intramolecular mechanism for formation of unsaturated structures and their location between carbons 5-6 were confirmed via (13)C NMR studies. High-level ab initio calculations showed that a 1-6 hydrogen transfer reaction was the most likely origin for these structures, though a second mechanism involving backbiting of the 1-2 C1 shifted head-to-head radical followed by beta-chlorine elimination and then transfer to monomer could also contribute at lower conversions. From the experimental analysis and theoretical calculations, it emerged that this backbiting reaction is stereoselective, with the isotactic conformation appearing to be more resistant. However, from the ab initio calculations and earlier results of other research groups it also seems likely that hydrogen abstraction from chloroallylic end groups and further propagation of such radical is a concurrent route to internal doublebonds. The evidence collected in this paper point to hydrogen abstraction reactions, especially backbiting and abstraction from chloroallylic end groups, as reactions for which inhibition should have a beneficial effect on the thermal stability of PVC. |
| Databáze: | OpenAIRE |
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