The Influence of Residual Olefin Structure on EPDM Vulcanization

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Abstract
While the results of our study leave many questions regarding vulcanization still open, it is concluded that: 1. Effective, practical vulcanization of polymers containing simple monoolefinic residues by sulfur/accelerator, sulfur donor/accelerator, p-quinone dioxime (or dinitroso benzene), and halogenated alkyl-phenol/formaldehyde resins demands that there be present hydrogen on carbon alpha to the double bond (allylic hydrogen). 2. Peroxide curing is most efficient when the olefinic moiety presents a vinyl or vinylidene group. In the case of the latter, reactivity is enhanced when the doubly-substituted, double-bonded carbon atom is part of a strained ring system. while allylic hydrogen is not necessary, its presence is advantageous in these low unsaturation elastomers. 3. The presence of sulfur in a peroxide cure generally decreases vulcanization efficiency, the more so the more active the olefinic residue in the unmodified vulcanization reaction. However, when main chain scissioning is a highly significant part of the overall reaction, the presence of sulfur can actually enhance vulcanization efficiency. 4. Conventional sulfur/accelerator vulcanization is quite sensitive to the nature of the olefinic residue present. Vulcanization rate, efficiency, and crosslink distribution can be affected. Hence, no far-reaching generalizations can be drawn regarding “best” structures beyond that made in Conclusion 1 though internal olefins appear most active. 5. Effective, practical vulcanization with halogenated alkylphenol/formaldehyde resins in an initially uncatalyzed system demands not only allylic hydrogen but also a 1,1-disubstituted or 1,1,3-trisubstituted ethylene moiety.

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