Mechanistic investigation of the formation of fluorinated polycyclic aromatic compounds during the thermal decomposition of polyvinylidene fluoride.

Abstract

The formation of products of incomplete destruction (PIDs) resulting from the thermal decomposition of the fluoropolymer polyvinylidene fluoride (PVDF) remains inadequately understood and is crucial for environmental impact assessments. The scarcity of analytical standards and challenges associated with sample collection constrains the experimental approaches aimed at product analysis. To address this challenge, computational modeling of the thermal degradation pathways of PVDF offers thermodynamically informed product distributions. The present study employs density functional theory (DFT) calculations to investigate the mechanisms of PVDF chain degradation through competing processes in inert high-temperature conditions. Here, we investigate temperature-dependence on fluoropolymer degradation mechanisms and elucidate the pathways contributing to the formation of 1,1-difluoroethylene, 1,1,3-trifluorobutadiene, hydrofluoric acid, and three types of (polycyclic)aromatic hydrofluorocarbons. A notable pathway discovered is the [4 + 2] Diels Alder reaction which builds up cyclic products, such as 1,3,5-trifluorobenzene, from smaller, highly abundant fragments.