BISCITRACONIMIDES AS ANTI-REVERSION AGENTS FOR DIENE RUBBERS - SPECTROSCOPIC STUDIES ON CITRACONIMIDE-SQUALENE ADDUCTS

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%).