Y. Martele

The thermal degradation process of some new synthesized polycarbonates is studied both from theoretical and experimental points of view to obtain microscopic insight into the factors that govern the reaction rates. Ab initio density functional theory calculations are performed on a set of carbonates, which are model systems for the polycarbonates. Kinetic parameters are determined by transition-state theory and compared with experimental-derived degradation temperatures. The study as presented here gives evidence of the existence of a correlation between these degradation temperatures and the reaction rates resulting from static ab initio calculations on small model systems that are representative for the active area of the degradation process. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

Thermal elimination reactions in carbonates are investigated from a theoretical point of view with density functional theory methods to obtain insight into the reaction mechanism and structural factors that influence the kinetics. Carbonate systems are good model systems for the kinetics of thermal degradable polycarbonates. Special attention is given to the influence of para-substituents placed either at Cα or Cβ. The results enable prediction of ρ values of the Hammett equation and confirm earlier experimental data.

Thermal elimination reactions on polycarbonates are investigated from both theoretical and experimental points of view, to obtain insight into the microscopic aspects that influence the reaction mechanism and rates. In particular, attention is focused on the influence of the type of substituents in the polymer chain on the reaction rates. Ab initio density functional theory calculations are performed on a series of model compound systems for the polycarbonates under study, in particular carbonates differing by the groups attached at the α and β carbon atoms. Reactants, products, and transition states are optimized at the B3LYP/6-311g** level of theory. The structures of the activated complex give insight into the mechanistic details of this type of Ei elimination reactions. The Cα−O bond dissociates before the Cβ−H bond, developing some carbocation character in the transition state on the Cα atom. The kinematics of the thermal decomposition reactions have been studied by means of transition state theory by construction of the microscopic partition functions. It turns out that the rates of the Ei elimination reactions are increased by the presence of those substituents on the Cα and Cβ carbon atoms which are stabilizing the carbocation character in the transition state. In a second part, degradation temperatures have been experimentally measured for some polycarbonates through thermogravimetric analysis. It is investigated whether the relative rates of the model compound carbonate systems are representative of the behavior of the thermal degradation temperatures in polycarbonates. The study as presented here proves that ab initio calculations on small model systems, which are representative for the active area of the degradation process in polycarbonates, can provide insight into the principal ingredients that govern the reaction rates.