Phase behavior of biodegradable amphiphilic poly(l,l-lactide)-b-poly(ethylene glycol)-b-poly(l,l-lactide)

This study describes the miscibility phase behavior in two series of biodegradable triblock copolymers, poly(l-lactide)-block-poly(ethylene glycol)-block-poly(l-lactide) (PLLA–PEG–PLLA), prepared from two di-hydroxy-terminated PEG prepolymers (Mn = 4000 or 600 g mol−1) with different lengths of poly(l-lactide) segments (polymerization degree, DP = 1.2–145.6). The prepared block copolymers presented wide range of molecular weights (800–25,000 g mol−1) and compositions (16–80 wt.% of PEG). The copolymer multiphases coexistance and interaction were evaluated by DSC and TGA. The copolymers presented a dual stage thermal degradation and decreased thermal stability compared to PEG homopolymers. In addition, DSC analyses allowed the observation of multiphase separation; the melting temperature, Tm, of PLLA and PEG phases depended on the relative segment lengths and the only observed glass transition temperature (Tg) in copolymers indicated miscibility in the amorphous phase.