Alternating copolymers having a stereoregular polyester structure

In the presence of catalysts acting through an anionic mechanism (alkyls or alcoholates of lithium), it was possible to obtain alternating crystalline copolymers of dimethylketene with some aromatic and heterocyclic aldehydes (having the general formula RCHO) consisting of macromolecules in which the repeating unit corresponds to the formula: magnified image Owing to the presence of an asymmetric carbon atom in the repeating unit of the products obtained, this copolymerization represents the first example of stereospecific synthesis of polyesters. The chemical structures of the copolymers obtained have been demonstrated by chemical and infrared analyses and by the identification of the products obtained by hydrogenolysis with LiAlH4. The preparation of alternating copolymers of dimethylketene with various aldehydes and the properties of the products are described. Furthermore a possible reaction mechanism according to which the two monomers are simultaneously coordinated to a molecule of the catalyst is proposed.