Crystal structure of alternating propylene-carbon monoxide copolymers of varying stereo- and regioregularity

The structure of alternating propylene-carbon monoxide copolymers was studied. The polymers were synthesized either without any regularity control or with the use of an enantioselective catalyst. It turned out that poly(propyleneketone) crystallizes with the formation of two lattice types depending on the conditions of its synthesis. Samples consisting of a mixture of two enantiomers form a streocomplex crystallizing with the formation of a triclinic lattice. As the number of attachment defects increases, the melting point notably decreases and amounts to 68°C for samples synthesized without any regularity control. Nevertheless, the process of stereocomplex formation remains energetically favorable, a fact explained by the existence of a selective interaction between the helices.