EPITAXIAL CRYSTALLIZATION OF POLYMERS ONTO BENZOIC-ACID - POLYETHYLENE AND PARAFFINS, ALIPHATIC POLYESTERS, AND POLYAMIDES

In the reported experiments, epitaxial crystallization of polyethylene, n-paraffins, aliphatic polyesters, and various polyamides has been achieved on benzoic acid crystal substrates, specifically on their (001) crystals faces, which are made up of the aromatic rings. The epitaxial relationship is very similar for all polymers investigated: it is characterized by a unique chain orientation (parallel to the b axis of the substrate) and a plane of contact which is either the b-c plane of polyethylene, or crystallographically similar ones for polyesters, or the plane of the hydrogen-bonded sheet for polyamides. Since benzoic acid is structurally similar to its alkali-metal salts, it is inferred that the nucleating efficiency of the latter toward chemically different but structurally similar polymers may well rest on an epitaxial relationship. Finally, the highly oriented morphology made it possible, for some polyesters with a monoclinic cell, to determine the angle between the chain axis and the Z axis of the optical indicatrix, a quantity not measured so far in polymers.