Study on the Mechanism of Triazine Thiol Cross-linking Reaction of Chlorinated Butyl Rubber by Density Functional Theory and the Role of Acid Acceptors

Abstract

This study aims to make clear the crosslinking mechanism between chlorinated butyl rubber (CIIR) and triazine thiol, a vulcanizing agent commonly used in medical rubber products, using density functional theory (DFT). It also examines the role of acid acceptors in this process. Experimental results indicated that the crosslinking reaction could occur even in the absence of acid acceptors. However, an excess of triazine thiol led to curing reversion, which was mitigated by the addition of acid acceptors. DFT calculations suggested that the crosslinking reaction between triazine thiol and chlorinated isoprene units was a one-step process involving simultaneous dehydrochlorination and C-S bond formation. Ion chromatography (IC) measurements confirmed that chloride ions were generated and leached during the crosslinking reaction, but this leaching was suppressed by the addition of acid acceptors. Additionally, ¹³C NMR measurements verified the crosslinking reaction between CIIR and triazine thiol. These findings suggest that acid acceptors not only provide a site for the crosslinking reaction but also absorb the generated chlorine and hydrogen, forming a complex structure that inhibits chloride ion leaching. The insights gained from this study contribute to enhancing the quality and reliability of triazine-crosslinked CIIR medical rubber products.