Miscibility and phase structure of blends of poly(ethylene oxide) with poly(3-hydroxybutyrate), poly(3-hydroxypropionate), and their copolymers

The miscibility and phase behavior of poly(ethylene oxide) (PEO) blends with poly(3-hydroxybutyrate) (P(3HB)), poly(3-hydroxypropionate) (P(3HP)), and poly(3-hydroxybutyrate-co-3-hydroxypropionate)s (P(3HB-co-3HP)s) have been investigated by differential scanning calorimetry (DSC) and high-resolution solid-state C-13 nuclear magnetic resonance (NMR). Four bacterial P(3HB-co-3HP) samples with 3HP contents of 15, 25, 46, and 76 mol % have been used in order to investigate possible influence of the sequence structure of P(3HB-co-3HP)s on the miscibility and phase behavior of blends. These four P(3HB-co-3HP) samples have different thermal properties and crystallizability depending on the 3HP contents. The DSC thermal behavior of the blends revealed that the blends of PEO with P(3HB), P(3HP), and P(3HB-co-3HP)s were miscible over the whole composition range but the crystallization of blend components followed by phase separation exerted much influence on the phase structure of the blends. The results from solid-state NMR spectroscopy showed that the 50/50 binary blends of P(3HB)/PEO, P(3HB-co-15%3HP)/PEO, P(3HB-co-25%3HP)/PEO, and P(3HP)/PEO were phase-separated due to the presence of crystalline phase but miscible to some extent. Two components in these blend were found to be mixed on a range greater than 30-40 nm, with two crystalline phases and an amorphous phase of miscible two components coexisting.