Rn. Datta et al., BISCITRACONIMIDES AS ANTI-REVERSION AGENTS FOR DIENE RUBBERS - SPECTROSCOPIC STUDIES ON CITRACONIMIDE-SQUALENE ADDUCTS, Rubber chemistry and technology, 70(1), 1997, pp. 129-145
The mechanism of anti-reversion activity of biscitraconimides (BCI) du
ring rubber vulcanization has been investigated. Biscitraconimides for
m crosslinks by reaction with chain modifications which are formed dur
ing the reversion process. These additional crosslinks compensate for
the sulfidic crosslinks that are lost during the reversion. To allow s
tructural assignments of the adducts formed between rubber and citraco
nimides, squalene has been used as a simple model system in combinatio
n with the currently used additives and sulphur. The products were ide
ntified as Diels-Alder adducts of conjugated polyenes, formed during r
eversion, with citraconimide. The nuclear magnetic resonance (NMR) spe
ctroscopic assignments of the products are discussed. Furthermore the
quantification of squalene-BCI adducts via NMR and mass spectrometry (
MS) using C-13 labelled 1,3-bis (citraconimidomethyl) benzene (BCI-MX)
is described. It was found that under the applied conditions (2 h, 17
0 degrees C), approximately 80% of the citraconimide groups are conver
ted into squaiene-BCI adducts. Diels-Alder adducts are the main reacti
on products of the reaction. Products from an ene reaction are formed
as minor component (less than 20%).