The pyrolysis of hexafluoropropylene oxide

Critical Review of Thermal Decomposition of Per- and Polyfluoroalkyl Substances: Mechanisms and Implications for Thermal Treatment Processes

Per- and polyfluoroalkyl substances (PFASs) are fluorinated organic chemicals that are concerning due to their environmental persistence and adverse human and ecological effects. Remediation of environmental PFAS contamination and their presence in consumer products have led to the production of solid and liquid waste streams containing high concentrations of PFASs, which require efficient and cost-effective treatment solutions. PFASs are challenging to defluorinate by conventional and advanced destructive treatment processes, and physical separation processes produce waste streams (e.g., membrane concentrate, spent activated carbon) requiring further post-treatment. Incineration and other thermal treatment processes are widely available, but their use in managing PFAS-containing wastes remains poorly understood. Under specific operating conditions, thermal treatment is expected to mineralize PFASs, but the degradation mechanisms and pathways are unknown. In this review, we critically evaluate the thermal decomposition mechanisms, pathways, and byproducts of PFASs that are crucial to the design and operation of thermal treatment processes. We highlight the analytical capabilities and challenges and identify research gaps which limit the current understanding of safely applying thermal treatment to destroy PFASs as a viable end-of-life treatment process.

Molecular Insight into Real-Time Reaction Kinetics of Free Radical Polymerization from the Vapor Phase by In-Situ Mass Spectrometry

The combination of organic chemistry and chemical vapor deposition enables a unique way to deposit conformal, high quality polymer thin films from the vapor phase. Particularly initiated chemical vapor deposition (iCVD) has recently shown its great potential in many different application fields. With the ever-increasing demands on the process, the need for additional process refinement is also growing. In this study the enhancement of the iCVD process by in-situ mass spectrometry is presented. The approach enables insight into real-time reaction kinetics during the deposition process as well as identification of reaction pathways. Furthermore, the composition of the gas phase can be precisely controlled and spontaneously adjusted if necessary. Particularly the deposition of thin films with thicknesses in the low nanometer range and the deposition of copolymers can benefit from this approach. The presented approach enables enhanced process control as well as the ability to perform extensive kinetic studies.

Shock wave studies of the pyrolysis of fluorocarbon oxygenates. I. The thermal dissociation of C3F6O and CF3COF

The thermal decomposition of hexafluoropropylene oxide, C₃F₆O, to perfluoroacetyl fluoride, CF₃COF, and CF₂ has been studied in shock waves in Ar between 630 and 1000 K. The subsequent decomposition of CF₃COF has been followed between 1400 and 1900 K.

Perfluorocarbenes Produced by Thermal Cracking. Barriers to Generation and Rearrangement

Thermal crackings of substituted oxiranes to generate various perfluoroalkylcarbenes are examined using ab initio density functional theory. Such reactions are generalizations of a current technology for the preparation of difluorocarbene. Barriers for the generation of fluoro(perfluoroalkyl)carbenes by this approach are computed to be higher than those for generation of difluorocarbene; the difference is attributed primarily to the lower stability of the respective singlet carbenes. Once generated, however, the carbenes are reasonably stable with respect to unimolecular rearrangement, so that high selectivity for reaction with olefins, such as might be present in an unsaturated polymer, may be expected under typical experimental conditions. With respect to rearrangements of perfluorocarbenes, 1,2-alkyl shifts are lowest in energy, 1,2-fluorine atom shifts are higher, and 1,3-fluorine atoms shifts are highest of all; this ordering reflects the relative orbital energies of the sigma bonds broken in the respective migrations. In instances where thermal conditions required for oxirane cracking may be incompatible with other functionalities in the reaction medium, theory predicts that extrusion of SiF(4) from perfluorosilylalkanes may be an attractive alternative for perfluorocarbene generation.