Role of intermolecular interaction between hydrophobic blocks in block-selected inclusion complexation of amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) triblock copolymers with cyclodextrins

The influence of hydrophobic interaction between poly[(R)-3-hydroxybutyrate] blocks on block-selected inclusion complexation between amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide)) (PEO-PHB-PEO) triblock copolymers and α-cyclodextrin (α-CD) or γ-cyclodextrin (γ-CD) was studied by X-ray diffraction, differential scanning calorimetry (DSC), FTIR and 1H NMR. Due to the stronger hydrophobic interaction at higher temperature, the amphiphilic triblock copolymer tends to aggregate to form tighter core-shell sphere with PHB block in the core and PEO in the corona. Therefore, the CD threaded onto PEO blocks cannot further slide onto the PHB block, which resulted in a highly block-selected inclusion complex formation. Moreover, the DSC results indicated that the triblock copolymer coalesced from its ICs with hot water showed an increase in microphase separation compared with the as-synthesized triblock copolymer, which further supports our hypothesis that CD only selectively includes PEO blocks of the triblock copolymer at higher temperature.