Computational Insights into the Thermal Stability and Degradation Pathways of Poly(butylene adipate-co-terephthalate)

The thermal decomposition pathways, bond dissociation free energies, and product distributions of biodegradable poly(butylene adipate-co-terephthalate) (PBAT) copolymer under inert atmosphere have been investigated using density functional theory (DFT). Calculations at the B3LYP/6-311++G(d,p) level identified the most stable molecular geometries, and decomposition processes were thoroughly analyzed. Based on vibrational frequency analyses and bond dissociation energy calculations, three primary decomposition pathways (ptw1, ptw2, and ptw3) were characterized, and their Gibbs free energy changes were computed. The results indicated that pathway ptw1 (61.41 kcal/mol) has the lowest energy barrier and is the most thermodynamically favorable route for decomposition. Additionally, low molecular weight aliphatic compounds, CO₂, adipate, and terephthalate derivatives were determined as the primary decomposition products. These findings provide significant insights into the thermal stability of PBAT and the environmental impacts of its decomposition products, contributing to the development of sustainable polymer applications.