Raman analysis of inverse vulcanised polymers

Abstract

Inverse vulcanised polymers have received significant research attention on account of their easy, modifiable, and low-cost synthesis. These polymers are synthesized from the industrial by-product, elemental sulfur, resulting in a high sulfur content, which has many influences on the polymers’ behavior, and gives them their wide variety of valuable properties. Because of this, inverse vulcanised polymers have many industrially attractive applications, however the high sulfur content that is directly responsible for this, also makes the polymers challenging to analyse. As such, the structure of inverse vulcanised polymers is poorly understood, and although sensible theories exist, there is a lack of direct evidence derived from a complete understanding of the polymers’ bonding level structure. Presented here is the use of Raman spectroscopy to scrutinise better the nature of inverse vulcanised polymers. Several Raman spectroscopic techniques have been compared and contrasted, revealing what information can be obtained from Raman spectroscopy in regard to these otherwise difficult to analyse polymers. Method optimisations are presented alongside computational studies and model compounds, all of which benefit the understanding of spectral information obtained from Raman spectroscopy. It was found that Raman spectroscopy is capable of providing several key pieces of information about inverse vulcanised polymers in a rapid and non-destructive way. These include, calculating the amorphous elemental sulfur content, assessing the homogeneity, tracking reactions in progress, and most crucially, identifying the proportions of different sulfur ranks of the polymer, which has thus far eluded all other analytical techniques.