MOLECULAR-ORIENTATION IN POLY(4-OXYBENZOATE-CO-1,4-PHENYLENE ISOPHTHALATE) BY SLOW-MAGIC-ANGLE-SPINNING DECODER NMR

Slow-magic-angle-spinning DECODER NMR based on the anisotropy of chemi cal shift tensors is used to determine molecular-level orientation in three samples of poly(4-oxybenzoate-co-1,4-phenylene isophthalate) of comparable composition but different process histories. The two-dimens ional NMR line shapes are sufficiently resolved to show quantitative d ifferences in the degree of orientation for powder, melt-extruded mono filament, and high-speed melt-spun fiber of the wholly aromatic liquid crystal polymer produced from an approximately equimolar mixture of 4 -hydroxybenzoic acid, hydroquinone, and isophthalic acid. By direct co mparison of calculated and experimental NMR line shapes, the full orie ntation distribution functions for all repeat units were determined an d found to be consistent with a combination of isotropic and anisotrop ic components. Multiple reorientation angles are used to confirm the p roposed molecular orientation distributions. The results indicate a hi gh degree of orientation in the melt-spun fiber, a lesser degree of or ientation in the melt-extruded monofilament, and isotropic orientation in the powder sample. Legendre polynomial expansions up to order n = 14 were estimated.