Recuring Vulcanizates. I. A Novel Way to Study the Mechanism of Vulcanization

1992 ◽  
Vol 65 (1) ◽  
pp. 211-222 ◽  
Author(s):  
Robert W. Layer
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Zinc Salt ◽  
Current View ◽  
Accelerator Complex ◽  
Exchange Reactions ◽  
Model Compounds ◽  
Vulcanization Process ◽  
Weight Model ◽  
Sulfur Donor

Abstract Vulcanizates, to which a curative is added by swelling, can be recured to easily study a variety of aspects of the vulcanization process, such as maturation, reversion, and even how much accelerator remains active as its zinc salt at the end of the cure. In effect, vulcanizates can be viewed as high-molecular-weight model compounds. In this study, we find that recuring SBR/BR vulcanizates, to which sulfur or the sulfur donor, N,N′ -dithiodimorpholine, is added, develops the same state of cure as the same amount of sulfur (or sulfur donor) added for the initial cure. This suggests that exchange reactions occur between crosslinks and the zinc-sulfur-accelerator complex during the cure and that all of the accelerator remains as its zinc salt at the end of the cure. This last result is interesting, since it is not consistent with the current view that most of the accelerator becomes irreversibly bound to the rubber and lost during the vulcanization of polybutadiene rubbers.

A study of the structure-mesomorphism relationship in some polymers and low-molecular-weight model compounds

1990 ◽  
Vol 26 (11) ◽  
pp. 1259-1265 ◽  
Author(s):  
Joaquin Barbera ◽  
Enrique Melendez ◽  
Fernando Navarro ◽  
Jose L. Serrano
Keyword(s):  
Molecular Weight ◽  
Low Molecular Weight ◽  
Model Compounds ◽  
Weight Model

Ultrafast and Reversible Multiblock Formation by the SET-Nitroxide Radical Coupling Reaction

2010 ◽  
Vol 63 (8) ◽  
pp. 1227 ◽  
Author(s):  
Jakov Kulis ◽  
Craig A. Bell ◽  
Aaron S. Micallef ◽  
Michael J. Monteiro
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Elevated Temperatures ◽  
Click Reaction ◽  
Coupling Reaction ◽  
Nitroxide Radical ◽  
Self Healing ◽  
Exchange Reactions ◽  
Radical Coupling ◽  
End Groups

The single electron transfer-nitroxide radical coupling (SET-NRC) reaction has been used to produce multiblock polymers with high molecular weights in under 3 min at 50°C by coupling a difunctional telechelic polystyrene (Br-PSTY-Br) with a dinitroxide. The well known combination of dimethyl sulfoxide as solvent and Me6TREN as ligand facilitated the in situ disproportionation of CuIBr to the highly active nascent Cu0 species. This SET reaction allowed polymeric radicals to be rapidly formed from their corresponding halide end-groups. Trapping of these carbon-centred radicals at close to diffusion controlled rates by dinitroxides resulted in high-molecular-weight multiblock polymers. Our results showed that the disproportionation of CuI was critical in obtaining these ultrafast reactions, and confirmed that activation was primarily through Cu0. We took advantage of the reversibility of the NRC reaction at elevated temperatures to decouple the multiblock back to the original PSTY building block through capping the chain-ends with mono-functional nitroxides. These alkoxyamine end-groups were further exchanged with an alkyne mono-functional nitroxide (TEMPO–≡) and ‘clicked’ by a CuI-catalyzed azide/alkyne cycloaddition (CuAAC) reaction with N3–PSTY–N3 to reform the multiblocks. This final ‘click’ reaction, even after the consecutive decoupling and nitroxide-exchange reactions, still produced high-molecular-weight multiblocks efficiently. These SET-NRC reactions would have ideal applications in re-usable plastics and possibly as self-healing materials.

Heat-induced changes in sulphydryl and disulphide levels of β-lactoglobulin A and the formation of polymers

1976 ◽  
Vol 43 (3) ◽  
pp. 411-418 ◽  
Author(s):  
K. Watanabe ◽  
H. Klostermeyer
Keyword(s):  
Heat Treatment ◽  
Molecular Weight ◽  
High Molecular Weight ◽  
Exchange Reactions ◽  
Anaerobic Conditions ◽  
Aerobic Conditions ◽  
Ph Values ◽  
Different Temperatures ◽  
Induced Changes ◽  
Β Lactoglobulin

SummaryThe effects of heat and pH on sulphydryl (–SH) and disulphide (–SS–) groups of β-lactoglobulin (β-lg) A have been studied by heating at different temperatures and pH values in air and at pH 6·9 in the absence of air. At pH 6·9 under aerobic conditions a decrease of –SH groups and an increase of –SS– groups was observed with increasing time and temperature. Only small changes were found under anaerobic conditions. At pH from 3·0 to 9·8 the –SH level decreased while the –SS– level increased up to pH 6·9 and then dropped rapidly. In addition to –SH/–SS– interchange there were reactions to other sulphur-containing compounds as seen from the losses in the total amount of –SH plus –SS– sulphur. The results of gelchromatographic investigations suggest that –SH-initiated –SS– exchange-reactions play an important role in the formation of high molecular weight polymers of β-lg A during heat treatment, and that the formation of intermediates depends on the presence of air.

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