Crystalline structure of poly(hexamethylene adipate). Study on the morphology and the enzymatic degradation of single crystals.
The crystalline structure of polyester 6 6 was studied by means of X-ray and electron diffraction and real-space electron microscopy. An orthorhombic unit cell containing eight chain segments with a quasi planar zigzag conformation was derived. The chain axis projection could be defined by a small rectangular cell containing only two molecular segments. Simulation of electron diffraction patterns indicates that molecular segments were arranged with azimuthal angles close to +/-46 degrees . X-ray diffraction patterns suggested that the large dimensions of the unit cell were a consequence of a slight shift between neighboring chains that improved the electrostatic interactions. Chain-folded lamellar crystals were obtained by isothermal crystallization of dilute n-hexanol or n-octanol solutions. The crystalline habit was studied, and the influence of temperature was evaluated. A regular folding surface was observed by using polyethylene decoration techniques. Lamellar crystals were easily degraded with different lipases. A preferential enzymatic attack was, in some cases, observed to occur in the crystal edges, giving rise to highly irregular borders with a fringed texture.