Poly(CL/DLLA-b-CL) multiblock copolymers as biodegradable thermoplastic elastomers

Lactic acid and ∑-caprolactone based polymers and their derivates are widely used in biomedical applications. Different properties are introduced by modifying the composition. In this study, poly(ε-caprolactone/D,L-lactide)-b-poly(ε-caprolactone) multiblock copolymers were synthesized as poly(ester-urethane)s (PEUs) by polymerizing in two steps involving ring-opening polymerization of precursors and by diisocyanate linking of precursors to produce thermoplastic elastomers (TPEs). The precursors and products were characterized by SEC, 1H-NMR and DSC, and dynamic mechanical study (by dynamic mechanical analysis, DMA) as well as morphological characterization (by transmission electron microscopy, TEM) of the product TPEs was carried out. Tensile and creep recovery properties of them were also studied. According to the characterizations, all the polymerizations were successful, and the prepared TPEs showed clear elastic behavior. In the DMA scans, rubbery plateau in the storage modulus curves between Tg and terminal flow region was clearly detectable indicating elasticity. The TEM images demonstrated phase separation of amorphous and crystalline blocks when the degree of crystallinity of the hard blocks was high enough. The elongations of TPEs varied between 800–1800%, while the modulus was 7–66 MPa. Two different types of recovery tests indicated the creep properties of TPEs to be highly dependent on the degree of crystallinity