The miscibility and phase behavior of two stereoisomer forms of poly(lactide) (PLA: poly (L-lactide) (PLLA) and poly(DL-lactide) (PDLLA)) blends with poly(epsilon-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) and PCL-b-monomethoxy-PEG (PCL-b-MPEG) block copolymers have been investigated by differential scanning calorimetry (DSC). The DSC thermal behavior of both the blend systems revealed that PLA is miscible with the PEG segment phase of PCL-b-(M)PEG but is still immiscible with its PCL segment phase although PCL was block-copolymerized with PEG. On the basis of these results, PCL-b-PEG was added as a compatibilizer to PLA/PCL binary blends. The improvement in mechanical properties of PLA/PCL blends was achieved as anticipated upon the addition of PCL-b-PEG. In addition, atomic force microscopy (AFM) measurements have been performed in order to study the compositional synergism to be observed in mechanical tests. AFM observations of the morphological dependency on blend composition indicate that PLA/PCL blends are immiscible but compatible to some extent and that synergism of compatibilizing may be maximized in the compositional blend ratio before apparent phase separation and coarsening.

Bacterially synthesized poly(3-hydroxybutyrate-co-3-hydroxypropionate) [P(3HB-co-3HP)] samples were compositionally fractionated using solvent/nonsolvent fractionation techniques. Binary blends between these compositionally fractionated P(3HB-co-3HP) samples, with much narrower comonomer compositional distribution, were prepared, and their thermal and crystallization behavior were studied using differential scanning calorimeter (DSC) and polarized optical microscopy. It was found that, in the amorphous phase of these blends, the miscibility mainly depends on the difference of 3HP contents (or 3HB contents) between the two components of the blend. When the difference of 3HP content between two copolyesters is less than 30-40 mol %, they become miscible in the amorphous phase. The type of crystal lattice, miscibility, and difference of the spherulite growth rate between the two components of the blend appear to be the important factors controlling the crystalline phase behavior. The results are compared with those of unfractionated P(3HB-co-3HP)s and the effects of comonomer composition and its distribution on the properties of unfractionated copolymers are discussed.

The miscibility and phase behavior of poly(ethylene oxide) (PEO) blends with poly(3hydroxybutyrate) (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 13 C 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.

Atactic poly(3-hydroxybutyrate) (a-PHB) and block copolymers of poly(ethylene glycol) (PEG) with poly(-caprolactone) (PCL-b-PEG) were synthesized through anionic polymerization and coordination polymerization, respectively. As demonstrated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) measurements, both chemosynthesized a-PHB and biosynthesized isotactic PHB (i-PHB) are miscible with the PEG segment phase of PCL-b-PEGs. However, there is no evidence showing miscibility between both PHBs and the PCL segment phase of the copolymer even though PCL has been block-copolymerized with PEG. Based on these results, PCL-b-PEG was added, as a compatibilizer, to both the PCL/a-PHB blends and the PCL i-PHB blends. The blend films were obtained through the evaporation of chloroform solutions of mixed components. Excitingly, the improvement in mechanical properties of PCL/PHB blends was achieved as anticipated initially upon the addition of PCL-b-PEG.

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