Molecular orientation distributions in poly(ethylene terephthalate) thin films and fibers from multidimensional DECODER NMR spectroscopy

Abstract

Multidimensional DECODER NMR experiments are applied to several industrial samples of poly(ethy1ene terephthalate) (PET) thin films and fibers, exploiting natural-abundance 13C resonances from different carbon sites to quantify orientational order in these materials. In two-dimensional (2D) DECODER NMR, the sample is flipped through a discrete angle during the mixing time of a 2D exchange NMR experiment. This allows frequencies at two spatial orientations to be correlated to elucidate molecular order in the sample. The theoretical background needed to analyze the corresponding 2D pattern in terms of angular distributions is outlined, and reconstruction of relevant one-dimensional slices through the orientation distribution is demonstrated. In PET fibers, direct reconstruction produces an orientation distribution that is at least bimodal; 60% of the chains are highly oriented, with a full-width-at-half-maximum (fwhm) of 20". The angle between the phenylene para axis and the fiber axis is determined to be 18 * 4". For biaxially drawn films, the direct reconstruction of slices through the orientation distribution shows that in a highly oriented fraction (ca. 80%) of the sample, the chain axes are confined to the film plane (fwhm of 15"), while the in-plane distribution of chain axes is much broader (fwhm of ca. SO"); the phenylene rings and carboxyl group planes are oriented preferentially parallel to the plane of the film (fwhm of 55"). Film samples collected at different points across an industrial sheet of PET are shown to exhibit sizable variations in ordering. For the center of the sheet, a slight preferential orientation along the transverse direction is clearly detected. Increased alignment of the PET chains (fwhm of 557, with the preferred orientation rotated toward the machine direction, is observed near the sheet edge. In uniaxial films, the fwhm of the orientation distribution is measured to be 85". A 3D DECODER experiment is implemented to separate frequency patterns that overlap in two dimensions.

Determination of Molecular Orientational Order in Cold-Stretched Poly(p-phenylene vinylene) Thin Films by DECODER 13C NMR

“…From our DECODER experiments and simulations, we estimated the value for s zz to be 18 ppm; as opposed to 30 ppm; as reported previously [39]. The 13 C tensor values listed in Table 1 for the protonated carbons in the aromatic ring are similar to those for aromatic sites in other polymers (for example, poly(ethylene terephthalate)) [28]. The values obtained for the vinyl carbons differ from values determined for polyacetylene.…”

“…The strongly overlapping spectra of the four distinct sites in PPV present challenges to the DECODER experiments and analyses of the PPV films, compared to previous DECODER studies, for example, of PET [28].…”

“…The DECODER method is an extension of an earlier experiment first introduced by Henrichs [27], which applied a discrete macroscopic reorientation of a sample to determine orientation distribution moments for films of poly(ethylene terephthalate) (PET) [27]. DECODER NMR extends Henrichs's approach to include reconstruction of the orientation distribution and has been implemented to study orientational order in deuterated polyethylene films [25], PET films and fibers [28], and high tensile strength fibers of poly(p-phenyleneterephthalamide) [29].…”

The molecular structure of spider dragline silk: Folding and orientation of the protein backbone

“…2, we tried to extract the orientational distribution function P(␣ F , ␤ F ) by using a regulatory approach equivalent to that used for the DOQSY spectra. The regulatory analysis did not yield a stable result, though, and we resorted to measuring 2D spectra, which correlate the 1D spectra at two different sample orientations [DECODER spectroscopy (42,43)]. Experimental DECODER spectra, fits, and PDFs for an experiment 60°3 30°are shown in Fig.…”

Solid-State 13C NMR Analysis of the Crystalline–Noncrystalline Structure and Chain Conformation of Thermotropic Liquid Crystalline Polyester

“…For comparison, the corresponding values for dimethoxy benzene (DMB) and diethoxy benzene (DEB) crystals 33 as well as for poly(ethylene terephthalate) (PET) 34 are given in this table. Chemical shift anisotropy j 11 À 33 j of the aromatic CH carbon for the BB-8 sample seems not Figure 9.…”