Investigating the Role and Scope of Catalysts in Inverse Vulcanization
Liam James Dodd, Ömer H. Omar, Xiaofeng Wu, Tom Hasell
Abstract
Inverse vulcanization is a potential route to the use of the large excesses of elemental sulfur, creating high-sulfur-content polymers with many potential applications. The addition of a metal diethyldithiocarbamate catalyst was previously found to bring several benefits to inverse vulcanization, making the process more attractive industrially. Herein is reported the establishment and exploration of a library of catalysts for inverse vulcanization. Three ranges of catalysts and up to 32 compounds and their combinations have been investigated. By trialing these alternative catalysts, several tentative deductions about the mechanism have been made. It has been found that stronger nucleophiles give a greater rate enhancement, but with the tradeoff that harder bases may promote hydrogen sulfide byproduct formation. Monomer binding by the cation may be a crucial mechanistic step, and it is possible that the catalysts act as phase transfer agents between the immiscible sulfur and organic phases. Additionally, the versatility of catalytic inverse vulcanization has been demonstrated with several different comonomer families.