Structural evolution during inverse vulcanization

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Synthesis

Background:

• Inverse vulcanization is a method for synthesizing polysulfides using elemental sulfur (S8).
• The detailed mechanism and product evolution during inverse vulcanization remain poorly understood.
• Understanding these processes is crucial for controlling the properties of resulting polysulfide materials.

Purpose of the Study:

• To elucidate the mechanism and product evolution during inverse vulcanization.
• To characterize the different stages of the inverse vulcanization process.
• To investigate the influence of various monomers on polysulfide network formation and stability.

Main Methods:

• Monitoring inverse vulcanization using rheological measurements to obtain characteristic curves.
• Analyzing the degradation pathways of polysulfide networks formed from different monomers (aromatic alkenes, olefins, dicyclopentadiene).
• Employing computational calculations to confirm proposed reaction mechanisms.

Main Results:

• Inverse vulcanization proceeds through three distinct stages: induction, curing, and over-cure.
• Polysulfide network stability and degradation mechanisms vary significantly with monomer type.
• Aromatic alkenes lead to thiocarbonyl formation and network degradation, while olefins yield thiophenes and slower degradation.
• Dicyclopentadiene shows a plateau in the over-cure stage.

Conclusions:

• The study clarifies the stages and mechanisms of inverse vulcanization.
• Monomer choice critically influences polysulfide network structure, stability, and degradation pathways.
• Computational analysis supports proposed reaction mechanisms involving sulfur-substituted alkenyl intermediates.