Molecular dynamics simulations of poly(ethylene 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 1 to 10 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 increases. The scaling exponents for the average chain radius of gyration and end-to-end distance are 0.594 and 0.571, respectively. The values of the heat capacity, isothermal compressibility, and thermal expansivity agree well with the available experimental data, which are of much longer PET chains. The scaling exponents for the self-diffusivity and zero-shear-rate viscosity are, respectively, -2.01 and 0.96, with the latter one being close to the theoretical prediction 1.0 for short-chain polymers.

A coarse-grained (CG) model of poly(ethylene terephthalate) (PET) was developed and implemented in CG molecular dynamics (MD) simulations of PET chains with degree of polymerization up to 50. The CG potential is parametrized to structural distribution functions obtained from atomistic simulations [J. Phys. Chem. B2010114786] using an inversion procedure based on the Ornstein−Zernike equation with the Percus−Yevick approximation (OZPY) [ Phys. Rev. E201081061204]. The CGMD simulation of PET chains satisfactorily reproduces the structural and dynamic properties from atomistic MD simulation of the same systems. We report the average chain end-to-end distance and radius of gyration, relaxation time, self-diffusivity, and zero-shear-rate-viscosity’s dependence on degree of polymerization. For the longest chains, we find the scaling exponents of 0.51, 0.50, and −2.00 for average chain end-to-end distance, radius of gyration and self-diffusivity, respectively. The exponents are very close to the theoretical values of entangled polymer melt systems (0.50, 0.50, and −2.0). The study of entanglement in the longer chains shows that the tube diameter, number of monomers between entanglement points and interentanglement strand length are in close agreement with the reported values for an entangled PET melt.

Smart biomaterials composed of pH responsive polymers, poly((meth)acrylic acid), were synthesized using a precipitation polymerization technique. The microparticles were grafted with poly(ethylene glycol) (PEG) chains that are capable of complexing with the hydroxyl groups of the polyacid and interpenetrating into the mucus gel layer upon entry into the small intestine. Upon introduction of an alkaline solution, these materials imbibe a significant amount of water and create a highly viscous suspension. These materials have the necessary physicochemical properties to serve as mucoadhesive controlled release drug carriers for the oral delivery of drugs.