The melting point of a polymer is determined by the
ratio between melting enthalpy and entropy, namely
T ¼ DH=DS. The DH differences among the samples
10:1, 20:1, 40:1 are not significant, but they have the
tendency to increase. Meanwhile this melting point decreases.
This means that DS must be increasing. With
the content of lactide increasing in the feeding ratio, the
amount of short-branched chain rises in the copolymer
(see discussion in 1H NMR sections); therefore, the
conformation entropy must also increase, and the
melting points have a tendency to drop. The dropping
range for short side chains from 10:1 to 20:1 is less than
from 20:1 to 40:1; meanwhile, the decreasing extent of
the melting point of the copolymer obeys the same
trend