Thermodynamics of the Carbon Dioxide–Epoxide Copolymerization and Kinetics of the Metal-Free Degradation: A Computational Study

The copolymerization reactions of carbon dioxide and epoxides to give polycarbonates were examined by density functional theory (DFT), and chemically accurate thermochemical data (benchmarked to experimental values) were obtained via composite ab initio methods. All of the examples studied, i.e., formation of poly(ethylene carbonate), poly(propylene carbonate), poly(chloropropylene carbonate), poly(styrene carbonate), poly(cyclohexene carbonate), and poly(indene carbonate), exhibited enthalpies of polymerization of 21–23 kcal/mol, with the exception of poly(cyclopentene carbonate) (15.8 kcal/mol) which suffers both ring strain and intramolecular steric repulsion caused by the cyclopentane ring fused to the polymer chain. The metal-free carbonate backbiting reaction by a free anionic polycarbonate strand is inhibited by bulky groups at the methine carbon but is accelerated by resonance stabilization of the pentavalent transition state in the case involving poly(styrene carbonate). Nucleophilic attack at th...