Page 250 - Handbook of Plastics Technologies

ELASTOMERS

4.42 CHAPTER 4

the action of accelerated-sulfur vulcanization systems. Reaction schemes for these two
types of vulcanization can be written as shown in Schemes 10 and 11.
As shown, the chemical structural requirements for these types of vulcanization are
that the elastomer molecules contain allylic hydrogen atoms. The attacking species from
the vulcanization system must contain sites for proton acceptance and electron acceptance
in proper steric relationship. This will then permit the rearrangement shown in Scheme 12,
where A is the proton acceptor site and B is the electron acceptor site.
This is an explanation for the fact that this type of vulcanization is not enabled by dou-
ble bonds per se, without allylic hydrogens in the elastomer molecules. (It should be
pointed out that the phenolic curative can also act by a slightly different mechanism to
give cross-links that contain chromane structural moieties, the allylic hydrogens still being
required.)

SCHEME 10 Vulcanization by phenolic curatives.

SCHEME 11 Vulcanization by benzoquino-
nedioxime.

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