Synthesis and properties of completely crystalline POM copolymers

Extended chain crystals of polyoxymethylene copolymers have been prepared by cationic copolymerization of trioxane and dioxolane. These crystals do not contain amorphous regions and behave like an ideal solid solution of CH₂CH₂O units in the crystal of CH₂O units up to a mole fraction of x_CH2CH₂O = 0.1. Melting points, melting enthalpies, specific heat, density and lattice parameters were measured as a function of mole fraction up to x_CH2CH₂O = 0.2. Comparison of the dependence of lattice parameters on mole fraction for the extended chain crystals and melt or solution crystallized copolymers indicates, that in the semi-crystalline samples the comonomer units are not distributed at random between amorphous and crystalline phase but the comonomer units are enriched in the amorphous phase.