Melting behavior of hydrolyzable poly(oxyethylene)/poly(L‐lactide) copolymers

The melting behavior of poly(oxyethylene) (PEG)/poly(L‐lactide) (PLLA) triblock copolymers with PEG contents ≦18,3 wt.‐% was studied by differential scanning calorimetry and polarizing optical microscopy. The influence of the PEG segment contents and the hydrolysis of the PEG/PLLA copolymers on the melting process was investigated. The melting temperatures of the PLLA homopolymers decrease with increasing hydrolysis time up to 600 h, and the degree of crystallinity increases from 46 to 56%. This causes the arrangement of the chains more ordered. Therefore, the entropies of fusion (Δ S m ) of the PLLA homopolymers increase during the hydrolysis time up to 600 h. The melting temperatures of the PEG/PLLA copolymers decrease, while the recrystallization temperatures increase with increasing hydrolysis time up to 600 h. In addition, both the increases of PEG content and hydrolysis time of the PEG/PLLA copolymers cause a decrease of Δ S m . The PEG segments and the hydrolysis are responsible for the disordered arrangement of the chains.