Some remarks on amorphous and atactic α‐olefin polymers and random ethylene–propylene copolymers

Abstract

Abstract The necessity is pointed out to distinguish between an “amorphous” α‐olefin polymer and an “atactic” α‐olefin polymer. It is convenient to limit the term “atactic” only to those amorphous linear regularly head‐to‐tail polymers which possess the same chemical regularity as the corresponding tactic polymers, from which they differ only for the lack of steric regularity. A clear interpretation is given of the presence of bands at 1155 and 915 cm. −1 in the IR spectra of isotactic and atactic polypropylenes. The presence of these bands is due to the monomeric unit, with a regular head‐to‐tail arrangement. The absence of these bands in the propylene polymers obtained with the aid of cationic‐type catalysts depends on the presence of a very small content of monomeric units of this type. Finally the conclusion is drawn that the presence of the two above‐mentioned bands in the IR spectrum of the ethylene–propylene copolymers does not indicate the presence of long propylene sequences of the isotactic type, and therefore the existence of a block copolymer, but only the presence of the monomeric unit mentioned above.