ANGULAR CHARACTERIZATION OF POLYMER SURFACES BY FTIR ATR DICHROISM WITH A ROTATABLE TRUNCATED HEMISPHERIC CRYSTAL

The design and applications of a new attenuated total reflection attachment for an FTIR instrument are described in this paper for the objective of obtaining horizontal angular profiles of IR absorbances from several polymer surfaces. Uniaxially drawn or rolltruded polymers show peanut-shaped angular profiles, when plotted on a full 360-degrees horizontal plane. For poly(ethylene terephthalate), the band at 972 cm-1 due to the trans conformer of the ethylene glycol exhibited much greater anisotropy along the draw direction than the band for the gauche conformer at 899 cm-1. Biaxially drawn samples show increasingly larger circles with draw ratio, with the 972-cm-1 band showing the greatest increase. The trends observed by IR are generally supported by independent results from X-ray diffraction and birefringence used for the bulk orientation determination. A liquid-crystalline aromatic copolyester made by counterrotating die extrusion exhibits more complex profiles; one surface shows about 45-degrees orientation from the extrusion direction while the opposite surface shows 135-degrees orientation. The surface of rolltruded polypropylene shows very high uniaxial orientation along the extrusion direction.