³⁵Cl Nuclear Quadrupole Resonance: A Cl-specific Probe of Local Structural Motifs in PVC

³⁵Cl nuclear quadrupole resonance (NQR) and Density functional theory (DFT) computations are combined to characterize chlorine environments in polyvinyl chloride (PVC) and detect structural defects. Calculations validated against reference data enable to classify two main groups of signals: terminal and internal chlorines, the former having ∼1 MHz higher ν. We also predict distinct ³⁵Cl NQR signatures for chlorine vacancies and additional vicinal/geminal chlorines, resulting in an increased ν. Using this methodology, two types of PVC samples are analyzed: commercial high-MW and low-MW PVC. Both show numerous Cl environments associated with both terminal and internal Cl, as well as additional features indicating the presence of Cl defects. Analysis of a partially dechlorinated PVC reveals that dechlorination primarily occurs at the terminal positions, while multichlorinated sites are less reactive and remain mostly untouched. This combined computational-experimental approach demonstrates that ³⁵Cl NQR can sensitively distinguish chlorine sites in PVC, enabling the direct detection of defects relevant to stability, degradation, and recycling strategies.