The high-temperature crystallization of poly(p-phenylene terephthalamide) (PPTA) from dilute organic solutions was achieved through the introduction of a non-solvent, or precipitating agent, at the desired crystallization temperature. The morphology and crystal structure were examined for crystals produced from PPTA polymer with two different molecular weights (M,=46000 and 3430gmo1-1), using transmission electron microscopy. For the high-molecular-weight polymer, ribbon-like crystals were produced, while the low-molecular-weight polymer yielded small needles or platelets. In both cases, electron diffraction showed that the Northolt allomorph was obtained. For the high-molecular-weight polymer, the molecular axes were parallel to the ribbon axes in a chain-extended type structure. A hypothesis for the orientation of the low-molecular-weight PPTA in the small platelets, is also given.
Посилання на статтю:
Morphology and structure of poly(p-phenylene terephthalamide) crystallized from dilute organic solution* / Catheryn L. Jackson and Henri D. Chanzy // Polymer. – 1993. – Vol 34. – P. 5011-5015.