Effect of isomer and defect structure on the thermal stability of polyvinyl chloride: An experiment and molecular dynamics simulation

The relationship between molecular chain structure and thermal stability of polyvinyl chloride (PVC) was studied by experiment and molecular dynamics (MD) simulation. The experimental results of oven aging test, UV–Vis and 1H-NMR showed that the PVC samples generated fewer conjugated triene and total double bond during aging exhibited better thermal stability. The IR spectra of gas products indicated that thermal aging of PVC mainly generated hydrogen chloride (HCl) and low molecular weight hydrocarbon (CH2) between 50 and 500 °C. The PVC molecular chain model was constructed by MD simulation to study reaction pathways and products during PVC thermal aging, the results further confirmed that HCl and CH2 were the main products of PVC thermal aging. Besides, the thermal aging models of PVC with different isomers and defect structure were also established and calculated based on MD simulation. The results of MD simulation and 13C-NMR indicated that the CCl bond in the syndiotactic structure broke first and the 1,2-dichloride terminal was the most unstable defect structure. In a word, this work paves the way for the observation of the real-time structure evolution of PVC, especially during the aging process.