Supramolecular evolution over an initial period of biodegradation of lactide and caprolactone based medical (co)polyesters

Phase-structural changes and enthalpic relaxation behavior of poly(d,l-lactide) (PDLLA), poly(l-lactide) (PLLA) and poly(l-lactide-co-ε-caprolactone) (PLCL) copolymers with a lactide molar content ∼70% and having different randomness character (PLCLr1: R = 0.69; PLCLr2: R = 0.92) were evaluated over 7 days in phosphate buffered saline (PBS) at 37 °C. Results obtained by Temperature Modulated Differential Scanning Calorimetry (TMDSC) and Dynamic Mechanical Analysis (DMA) showed an increase in the value of enthalpic relaxation (δ) and the narrowing of the tan δ peak, respectively, indicating the reduction in molecular mobility and a more uniform distribution of the entropic states as the aging time increased. The results obtained for PLCLs were clearly affected by chain microstructural magnitudes, lLA (PLCLr1 = 4.35 and PLCLr2 = 3.45). Both showed a crystallization process accompanied by amorphous phase separation during the early stage in PBS. DSC and DMA results also revealed faster structural changes as a result of new supramolecular arrangements as well as a higher tendency to crystallize for PLCLr1 regarding PLCLr2.