CRYSTALLINE AND AMORPHOUS MORPHOLOGIES OF AN AROMATIC POLYIMIDE FORMED ON PRECIPITATION FROM SOLUTION

The solution-precipitated morphology of a new sulphonated aromatic polyimide, poly(benzophenone tetracarboxylic dianhydride 3,3'-diaminodiphenylsulphone) (BTDA 3, 3'-DDS), has been studied by transmission electron microscopy (t.e.m.) and wide-angle X-ray diffraction (WAXD). First, it has been shown that if held in solution in dimethylacetamide for an extended period, the polymer can crystallize as sheaf-like, multicrystallite aggregates that take on the appearance of axialites at a sufficiently advanced stage of growth. This morphology is very similar to that displayed by other relatively stiff polymers such as poly(ether ether ketone) (PEEK), poly(ether ketone) (PEK), and poly(phenylene sulphide). The generation of this general type of morphology is attributed to the inflexibility of the backbone, which renders folding difficult and hence leads to the production of a thick amorphous region on the lamellar surface, which then limits lateral crystal growth and creates a high density of cilia that cause nucleation of other crystals, leading to the formation of multilayered aggregates. Secondly, if the solvent is evaporated in moist air before crystallization can occur, a phase separation takes place on absorption of water vapour from the atmosphere. In this case the resulting polymer is amorphous and adopts a bead-like morphology on the scale of 300-2000 angstrom (1 angstrom = 10(-10) m).