Pyrolysis kinetics of gas-phase polyvinylidene fluoride (PVDF): a DFT study

Polyvinylidene fluoride (PVDF) is widely used in energetic materials and other fields. However, no detailed kinetic mechanism is available to describe the complete decomposition of PVDF in the gas phase. In this work, CH₃CF₂CH₂CF₂CH₂CHF₂ was selected as the PVDF model to build the complete decomposition mechanism. The potential energy surface for unimolecular and bimolecular reactions of PVDF decomposition was calculated via advanced quantum chemistry methods (DLPNO-CCSD(T)/cc-pVTZ//B3LYP-D3/6-311++G(d,p)). The temperature and pressure dependences of the rate constants of key reactions at 300–3000 K and high-pressure limits were calculated via the RRKM master equation method. The thermochemical properties of related species at the DLPNO-CCSD(T)/CBS level were calculated via the atomization method. Our calculations showed that the step-by-step decomposition of PVDF is dominated by HF elimination reactions, generating large amounts of HF and hydrofluoroolefins. In addition, the radical-driven (H, OH, and O) decomposition of PVDF produces small molecules such as H₂, H₂O, OH and fluoroalkyl groups. It is also found that further decomposition after H abstraction from the PVDF side chain is dominated by the β-C–C scission reactions, and the product structure is consistent with existing experimental studies. The simulation results show that the 1,2-HF elimination reactions control the initial and secondary decomposition of PVDF. The migration reactions and HF elimination reactions jointly promote the further conversion of PVDF into species with polyene sequences.