Impact of Concentration and Temperature on the Crosslinking of Butyl Rubber Using Triethylenediamine

A viscoelasticrubber must be crosslinked into a network. This removes the translational mobility of the chains but not the segmental mobility and result in an elastic solid. Crosslinking of butyl rubber, which is a copolymer composed mostly of isobutylene and a small fraction of isoprene, is difficult due to the low number of unsaturated bonds. Traditionally, the rubber is crosslinked via vulcanization, a process that requires high temperatures and a curative package composed of several chemical reagents. In this work, an ester-functionalized butyl rubber was examined formed by grafting pentafluoro propiolate onto the butyl rubber chain. This group is electron-withdrawing and made the unsaturated bonds more susceptible to crosslinking. In addition, two geminal C=C bonds were introduced to further enhance the reactivity. A base, triethylenediamine (TED), was used to crosslink the butyl rubber. The present crosslinking reaction can be carried out at temperature much lower than conventional vulcanization temperatures. Variation of the concentration of triethlyenediamine was found to affect the molecular weight between crosslinks. The crosslinking density initially increases with increasing base concentration and then decreases beyond a threshold value. This is believed to be a result of a side reaction becoming increasingly important as TED concentration is increased. As expected, crosslinking occurred faster at higher temperatures. The tensile strength of the rubber increased with increasing TED concentration to the same threshold value previously discussed then began to decrease.