MORPHOLOGY AND STRUCTURE OF POLY(P-PHENYLENE TEREPHTHALAMIDE) CRYSTALLIZED FROM DILUTE ORGANIC SOLUTION

The high-temperature crystallization of poly(p-phenylene terephthalami de) (PPTA) from dilute organic solutions was achieved through the intr oduction of a non-solvent, or precipitating agent, at the desired crys tallization temperature. The morphology and crystal structure were exa mined for crystals produced from PPTA polymer with two different molec ular weights (M(w) = 46 000 and 3430 g mol-1), using transmission elec tron microscopy. For the high-molecular-weight polymer, ribbon-like cr ystals were produced, while the low-molecular-weight polymer yielded s mall needles or platelets. In both cases, electron diffraction showed that the Northolt allomorph was obtained. For the high-molecular-weigh t polymer, the molecular axes were parallel to the ribbon axes in a ch ain-extended type structure. A hypothesis for the orientation of the l ow-molecular-weight PPTA in the small platelets, is also given.