From Polymerization to Pyrolysis: Mechanistic Pathways and Product Selectivity in Polyolefins and PVC in New Perspective

Plastics streams dominated by polyolefins and PVC demand a design framework that links synthesis to end-of-life reactivity. This work integrates polymerization-derived microstructure with depolymerization mechanisms to guide selective valorization. We synthesize mechanistic and kinetic evidence connecting coordination and radical polymerization (linear HDPE, branched LDPE, stereoregular PP; PVC with backbone C–Cl) to degradation pathways, and evaluate catalytic topologies (Brønsted/Lewis acidity, framework Al siting, micro/mesoporosity), initiators, and termination/quench strategies under relevant process variables (temperature, heating rate, vapor residence time, pressure). The analysis shows that microstructure prescribes reaction manifolds and attainable product slates: strong Brønsted acidity and shape-selective micropores favor C₂–C₄ olefins and BTX, whereas weaker acidity and hierarchical porosity preserve chain length to paraffinic oils/waxes; mesopore enrichment shortens contact times and suppresses secondary cracking; initiators lower onset energies and expand operability; diffusion management and surface passivation mitigate deactivation. For PVC, continuous HCl removal and basic/redox co-catalysts or ionic liquids lower dehydrochlorination temperatures and yield cleaner fractions, making staged dechlorination followed by residue cracking essential. Framing process design as “polymerization → structure → depolymerization” enables predictive yield targeting and energy-lean operation across mixed wastes, providing actionable guidance on catalyst selection, severity and residence-time control, regeneration, and integrated halogen management.