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

摘要

The mechanism of anti-reversion activity of biscitraconimides (BCI) during rubber vulcanization has been investigated. Biscitraconimides form crosslinks by reaction with chain modifications which are formed during the reversion process. These additional crosslinks compensate for the sulfidic crosslinks that are lost during the reversion. To allow structural assignments of the adducts formed between rubber and citraconimides, squalene has been used as a simple model system in combination with the currently used additives and sulphur. The products were identified as Diels-Alder adducts of conjugated polyenes, formed during reversion, with citraconimide. The nuclear magnetic resonance (NMR) spectroscopic 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, 170 degrees C), approximately 80% of the citraconimide groups are converted into squaiene-BCI adducts. Diels-Alder adducts are the main reaction products of the reaction. Products from an ene reaction are formed as minor component (less than 20%). [References: 17]