Morphological study of biodegradable PEO/PLA block copolymers.

A series of PEO/PLA copolymers, covering a wide range of compositions and segmental lengths, was synthesized, and their morphology was investigated by means of DSC and IR studies. For matrices comprising PEO chains with molecular weights below 3400, no soft-segment crystallinity was detected. When long hard segments were present, essentially monophasic, semicrystalline polymers were obtained, with PLA blocks melting around 130 degrees C. Polymers containing longer soft segments (PEO 6000) exhibited a two-phase matrix, with both components being able to crystallize. The relative degree of crystallinity of PEO and PLA blocks was also determined. The thermal history of the sample strongly affected the morphology of the matrix, especially when both blocks were long enough to crystallize. To further explore these polymers, solvent cast films were prepared and their morphology assessed. Casting from acetone, which is an excellent solvent for PLA, resulted in hard blocks exhibiting lower degrees of crystallinity, while methanol had a similar effect on PEO soft segments.