Molecular Orientation of Polymer Chains of Poly(ethylene 2,6-naphthalate) Determined Using Mueller Matrix Infrared Spectroscopic Ellipsometry Supported by Density Functional Theory Calculations

Biaxially-oriented semi-crystalline film of poly(ethylene 2,6-naphthalate) was investigated by mid-infrared Mueller matrix spectroscopic ellipsometry using a prototype instrument with a quantum-cascade laser as a source. The results were analyzed using a biaxial anisotropic model, and the absorption features are characteristic of the α phase of poly(ethylene 2,6-naphthalate). A comparison with density functional theory calculations of methyl ethyl 2,6-naphthalate, a model molecule consistent with the structure and conformation of α-poly(ethylene 2,6-naphthalate), reveals that the planes of naphthalene moieties of the polymer backbone are parallel to the surface. The parametrized model of biaxial dielectric function is reported.