Thermal properties of di- and triblock copolymers of poly(l-lactide) with poly(oxyethylene) or poly(ε-caprolactone)

High molecular weight di- and triblock copolymers of poly(l-lactide), PLLA, (80 wt%) with a crystallizable flexible second component such as poly(ε-caprolactone), PCL, or poly(oxyethylene), PEO, (20 wt%) were obtained in nearly quantitative yields by ring opening of l-lactide initiated by PCL or PEO hydroxy terminated macromers. The copolymers were characterized by 1H NMR and FTIR spectroscopy and size exclusion chromatography and showed unimodal and narrow molecular weight distributions. X-ray diffraction measurements revealed high crystallinity (38–56%) of the PLLA blocks and gave no clear evidences of PCL or PEO crystallinity. DMTA and DSC techniques showed a melting behaviour of the copolymers (Tm=174–175 °C; ΔHm=19–37 J/g) quite similar to that of PLLA. PCL and PLLA segments are immiscible, while PLLA and PEO segments are partially miscible in the amorphous phase. Stress–strain measurements indicated a ductile behaviour of the copolymers, characterized by lower tensile moduli (225–961 Pa) and higher elongations at break (25–134%) with respect to PLLA.