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 less-than-or-equal-to 18,3 wt.- % was studied by differential scanning calorimetry and polarizing opti cal microscopy. The influence of the PEG segment contents and the hydr olysis of the PEG/PLLA copolymers on the melting process was investiga ted. The melting temperatures of the PLLA homopolymers decrease with i ncreasing hydrolysis time up to 600 h, and the degree of crystallinity increases from 46 to 56%. This causes the arrangement of the chains m ore ordered. Therefore, the entropies of fusion (DELTAS(m)) of the PLL A homopolymers increase during the hydrolysis time up to 600 h. The me lting temperatures of the PEG/PLLA copolymers decrease, while the recr ystallization temperatures increase with increasing hydrolysis time up to 600 h. In addition, both the increases of PEG content and hydrolys is time of the PEG/PLLA copolymers cause a decrease of DELTAS(m). The PEG segments and the hydrolysis are responsible for the disordered arr angement of the chains.