Isodimorphic biodegradable copolyesters: Structure and crystallization behavior*

Random copolymers with crystallizable components can crystallize in three modes: (a) comonomer exclusion, in which the comonomer is excluded from the crystal lattice of the other component, (b) isomorphism (i.e., strict molecular requirements should be met), in which a single crystalline phase is observed for all compositions, because of comonomer inclusion, and (c) isodimorphism, where two crystalline phases are formed depending on the composition, and both phases allow comonomer inclusion. In the present invited lecture, the detailed structure, morphology, nucleation and crystallization behavior of isodimorphic biodegradable copolyesters will be presented as a function of their comonomer ratio. This information is very significant as it allows tailoring the properties of random copolymers as well as their applications. The materials exhibit a pseudo-eutectic type phase behavior. To the left and to the right of the pseudo-eutectic a single phase is formed, rich in the corresponding parent comonomer. However, near the pseudo-eutectic point, two crystalline phases can be formed. In this way, double crystalline materials with interesting spherulitic superstructures that contain both types of lamellar thickness can be generated. The applications of these materials are potentially very interesting as superstructures with different sensitivities to biodegradation could be prepared and their lifetime can be tailored from their structural characteristics.

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