Low-Temperature Processable Degradable Polyesters.

Block copolymers composed of a low-T(g) and high-T(g) block, with suitable pressure miscibility characteristics, can be formed at low-temperature through the application of pressure. Aliphatic block copolyesters composed of poly(ε-caprolactone) derivatives and poly(L-lactide) show room temperature processability under hydraulic pressure of 34.5 MPa without polymer degradation. Mechanism of the pressure-induced flow is investigated by small-angle X-ray scattering. A scattering associated with a lamellae structure observed at ambient conditions decreases with elevating hydrostatic pressures, indicating pressure-induced phase mixing. Traces of the pressure-induced phase transition are studied by differential scanning calorimetry and X-ray diffraction. Tensile test of the block copolymers reveals that the mechanical properties can be readily controlled by changing composition, molecular weight, and chemical structure of the blocks. Among them, the hard segment PLLA fraction is the key factor to characterize the properties. Young's modulus of the block copolyesters is similar to that of polyethylene.