title: Advancing the Synthetic and Analytical Techniques of Inverse Vulcanisation
Creators: name: Dodd, Liam
Publisher: name: University of Liverpool Repository
Year: 2024

description: Inverse vulcanisation is a diverse and versatile polymerisation reaction that reacts elemental sulfur 
with an olefinic organic compound to generate polymers that can contain large amounts of sulfur by 
mass. Such reactions usually entail a bulk polymerisation where sulfur is heated beyond its melting 
point, to temperatures where radical capped sulfur chains form. Upon cooling these chains are 
unstable, but they can be reacted with carbon – carbon double bonds to create inverse vulcanised 
polymers: organic units interconnected by chains of sulfur atoms. Normally the organic component 
would contain multiple olefinic moieties, such that the product is crosslinked, which is generally more 
stable than the less common examples of linear inverse vulcanised polymers. Inverse vulcanised 
polymers have a great many applications that make them attractive next generation materials, and 
many of these properties can be tuned by controlling how much sulfur is used in the synthesis. Even 
more exciting is the wide library of reactive olefins that are amenable to inverse vulcanisation, each 
bringing a new product polymer with a different complement of properties. What makes inverse 
vulcanisation so much more attractive, is that sulfur is an industrial by-product that is produced in vast 
excesses with supply greatly outweighing demand. Thus, elemental sulfur is remarkably cheap, and 
since the olefinic reactant can come from a renewable source, inverse vulcanisation can meet the 
principles of green chemistry. However, inverse vulcanisation suffers from a poorly understood 
mechanism, little to no regimentation in how syntheses are conducted, and severe issues in the 
analysis and understanding of the structure of the product polymers, which are issues that the work 
carried out in contribution to this thesis aimed to remedy with three topics. The first topic examine in 
this thesis is the catalysis of inverse vulcanisation, which can improve the yield and reaction time of 
inverse vulcanisation whilst inducing reaction in otherwise unreactive comonomers, and giving 
product polymers of better properties. By varying the catalyst structure, conclusions were drawn 
about what makes an effective catalyst and how such catalysts might work. As a follow on from the 
first, the second topic investigates metal free amine catalysts, which circumvent sustainability 
concerns of metal containing catalysts as well as metal contamination of the environment. As a natural 
branch to this project, previously under-investigated alkyne crosslinkers were studied, as well as a 
dispersion polymerisation method, useful for highly reactive crosslinkers. The final topic is the use of 
Raman spectroscopic analysis for characterisation of inverse vulcanised polymer structure, something 
near impossible by other means and which carries of wealth of critical but otherwise hard to obtain 
information, such as the sulfur chain length, the homogeneity, and the unpolymerized elemental 
sulfur content of the product polymer.