Atomistic and coarse-grained simulations of polyethylene terephthalate (PET) oligomers have been performed. Atomistic Molecular Dynamics (MD) simulations of polyethylene terephthalate (PET) oligomers are performed in the isobaric-isothermal (NpT) ensemble at a state point typical of a finishing reactor. The oligomer size ranges from one to ten repeat units. We report thermodynamic properties (density, potential energy, enthalpy, heat capacity, isothermal compressibility, and thermal expansivity), transport properties (self-diffusivity, zero-shear-rate viscosity, thermal conductivity), and structural properties (pair correlation functions, hydrogen bonding network, chain radius of gyration, chain end-to-end distance) as a function of oligomer size. We compare the results with existing molecular-level theories and experimental data. Scaling exponents as a function of degree of polymerization are extracted. The distribution of the end-to-end distance is bimodal for the dimer and gradually shifts to a single peak as the degree of polymerization (DP) increases. The scaling exponents for the average chain radius of gyration and end to end distance are 0.594 and 0.571, respectively, close to the theoretical value for polymer melts of 0.589. The values of the heat capacity, isothermal compressibility, and thermal expansivity agree well with the available experimental data, which is of much longer PET chains. The scaling exponents for the self-diffusivity and zero-shear-rate viscosity are respectively -2.01 and 0.96, close to the theoretical predictions of -2.1 and 1.0.
A coarse-grained potential for PET is developed based on pair correlation functions from the atomistic simulations. A comparison of the structural and dynamic results between the atomistic and coarse-grained simulations is provided.
This research was supported by the Eastman Chemical Company. This research project used resources of the National Institute for Computational Sciences (NICS) supported by NSF under agreement number: OCI 07-11134.5.
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