Structure and properties of naphthalene containing polyesters, 1. High resolution solid state13C NMR study of poly(ethylene naphthalene-2,6-dicarboxylate)

Abstract

Poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) crystallizes in two different modifications depending on the temperature of crystallization. The high resolution solid state 13 C NMR spectra of the α modification, β modification and amorphous PEN have been measured by employing cross polarization with magic angle spinning and high power proton decoupling. By application of both a short contact time pulse sequence and an interrupted decoupling pulse sequence all resonance lines, some of which are overlapped in the original 13 C CP/MAS NMR spectra of both amorphous and β modification PEN, are separated. The α modification PEN, β modification PEN, amorphous PEN and PEN in solution show different chemical shifts for each individual carbon atom. The chemical shift difference between amorphous PEN and PEN in solution is much smaller than the difference between either modification crystalline PEN and PEN in solution. The resonance lines of the naphthalene carbon atoms of crystalline PEN have been found to be at a lower field shift than the corresponding lines of PEN in solution. Conversely, the resonance lines of the other carbon atoms on crystalline PEN are shifted upfield from the ones of PEN in solution. A significant difference between the spectra of α and β form PEN can be observed in resonances of the protonated naphthalene carbon atoms C 1 , C 5 , C 4 , and C 8 . They differ by 1.10 ppm. These chemical shift differences are explained in terms of different conformation and chain packing in the samples.