Differential Scanning Calorimetry Study of Phase Transitions in Poly(lactide)−Chloroform−Methanol Systems

The phase separation processes occurring in poly(l-lactide) (PLLA)−chloroform−methanol mixtures and poly(dl-lactide) (PDLLA)−chloroform−methanol mixtures have been studied using differential scanning calorimetry, cloud point measurements, and optical microscopy. It is demonstrated that liquid−liquid demixing occurs in ternary solutions of PDLLA at sufficiently high methanol concentrations. For PLLA-containing solutions, both liquid−liquid demixing processes and solid−liquid demixing processes occur. The most important parameters for the phase separation process are the applied cooling rate and the polymer concentration. Nonequilibrium phase separation processes play an important role in the phase separation of ternary PLLA solutions. Due to the high activation energy needed for crystallization, liquid−liquid demixing will usually precede solid−liquid demixing even if solid−liquid demixing is favored thermodynamically. Only at low cooling rates and high polymer concentration does solid−liquid demixing take place without the interference of liquid−liquid demixing.