Thermal-Oxidation of Network Structures

Elastomeric materials undergo both thermal and oxidation degradation over time. Main chain scission and loss of sulfur crosslinks can occur with either factor or by both factors by a thermo-oxidative mechanism. 

Another study used 13C NMR to examine the thermal ageing of NR with both peroxide and conventional and EV sulfur vulcanised samples [59]. The samples were heat aged at 70 °C in air with 13C NMR recorded after 3 and 21 days. The vulcanisate structures vulcanised by peroxide and the EV sulfur system showed low sensitivity to ageing effects while peaks in the conventional sulfur system almost disappeared after 21 days of ageing. In addition, the main chain isoprene carbon peaks showed considerable broadening due to increasing stiffness of the network. 

From this chapter, it is clear that high resolution 13C NMR spectroscopy has made a large number of contributions to our knowledge of the structure of vulcanised crosslinked elastomers as well as the mechanism by which the vulcanisation process occurs. It is anticipated that further NMR measurements of these systems will continue to generate new structural and mechanistic information. 

The authors wish to acknowledge the support of the National Science Foundation as well as the support of the Yokohoma Rubber Company and the Pirelli Rubber Company. 

Chain Structure and Conformation of Macromolecules, Academic Press, New York, 1982. 

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