PREDICTING THE COCRYSTALLIZATION BEHAVIOR OF RANDOM COPOLYMERS VIA FREE-ENERGY CALCULATIONS

This contribution concerns the application of the thermodynamic-integr ation approach to crystalline structures. We calculate the defect Helm holtz energy of a single comonomer inclusion into the crystal structur e of the host polymer via molecular-dynamics simulations. It was found that prior to the commonly applied scaling of the force field paramet ers, an additional scaling of some bond lengths and a modification of the short-distance nonbonded interaction potentials were necessary to avoid singularities and numerical instabilities during the free-energy calculations. The resulting defect Helmholtz energies for single incl usions in the system poly(ethylene terephthalate-co-2,6-dicarboxy naph thanoate) were considerably larger than the thermal energy and prohibi t comonomer inclusion.