Polar packing structure in copolyester comprising 4-hydroxy benzoic acid and 6-hydroxy-2-naphthoic acid as studied by high resolution solid state 13C NMR spectroscopy and quantum chemistry

Abstract

The copolyester comprising 73 mol% of 4-hydroxy benzoic acid and 27 mol% of 6-hydroxy-2-naphthoic acid, so called Vectra, was known to show the strong second harmonic generation (SHG) when it has a high molecular weight. Using high-resolution solid state 13C NMR, we investigated the intermolecular interaction in this series of copolyesters with different inherent viscosities. The observed 13C NMR chemical shifts of carbonyl carbon moved downfield as the inherent viscosity is increased. The trend is similar to that observed in the inherent viscosity dependence of the SHG activity, showing that the downfield movement of the chemical shift is related to the polar structure. Ab initio GIAO–CHF calculations of NMR chemical shifts (NMR shieldings) were carried out for seven-molecules models with and without the polarity. The result confirms the assignment of the downfield movement of the chemical shifts to the transformation from the nonpolar structure to the polar structure.