Assessment of the Accuracy of Semi-Empirical Quantum Chemistry Calculations ofthe Mechanical Properties of Polymers

摘要

The ultimate mechanical properties of polymers, assuming perfect morphology, willbe limited by the mechanical properties of a single, ideal polymer chain. Previous calculations of polymer chain moduli using semi-empirical (SE) quantum chemistry methods have resulted in modulus values much higher than experimentally measured. This study investigated the error in the calculated inherent to the method of calculation by comparing SE results for C-C bond potentials in two well characterized polymers, polyethylene and polydiacetylene. It was found that the SE calculation systematically overpredicted bond stiffness in these polymers by approximately 25% to 30%. This is the upper limit on the modulus overprediction, depending on the importance of bond extension/compression (as compared to other deformation modes) in the overall deformation of the polymer chain.