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 alpha and beta 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 E(i) elimination reactions. The C(alpha)-O bond dissociates before the C(beta)-H bond, developing some carbocation character in the transition state on the C(alpha) 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 E(i) elimination reactions are increased by the presence of those substituents on the C(alpha) and C(beta) 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.

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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 C R or C β . The results enable prediction of F values of the Hammett equation and confirm earlier experimental data.

The micropatterning of a series new poly(carbonate‐urethanes) with IR and excimer lasers is discussed. A series of segmented polyurethanes consisting of a soft segment and a hard segment was prepared. The soft segment, a thermodegradable polycarbonate diol, degrades by a syn‐elimination at higher temperature. The hard segment was selected as to increase the sensitivity of the polymers for UV excimer laser ablation. The thermal and mechanical properties of the segmented polyurethanes (SPU) were investigated. By varying the building blocks in the polymer (soft and hard segments), the ablation properties were studied in terms of absorption coefficient and threshold value. Polymers with an aromatic chain‐extender and an diisocyanate showed the highest absorption coefficient at wavelengths of 248 and 193 nm. Irradiation of these polymers led to cavities with high dimensional quality, sharp edges and no accumulation of degradation products near the cavities (no debris formation). Ablation with an IR laser led to a decrease in film thickness of the polymer deposited on a substrate. This was investigated with FTIR/ATR analysis and atomic force microscopy. Debris formation was found near the cavities. The differentiation of polarity between the exposed and unexposed areas was not efficient enough to use them as a coating for printing plates. © 2002 Society of Chemical Industry

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