Thermal and Infrared Spectroscopic Studies on Hydrogen-Bonding Interaction between Poly(3-hydroxybutyrate) and Catechin

The effects of catechin on the properties of bacterially synthesized isotactic poly[(R)-3-hydroxybutyrate] (i-PHB) and chemosynthesized highly-syndiotactic poly[(R,S)-3-hydroxybutyrate] (s-PHB) were investigated by differential scanning calorimetry and Fourier transform infrared (FT-IR). In both PHB/catechin blend systems, the composition-dependent single glass transition temperature was observed. By using FT-IR, the formation of intermolecular hydrogen bonds was found between the carbonyl of PHB and the hydroxyl of catechin. The strength of intermolecular hydrogen bonds of s-PHB/catechin blends, i-PHB /catechin blends and pure catechin is in this order, i.e., s-PHB/catechin blends < i-PHB/catechin blends < pure catechin. The crystallization of either i-PHB or s-PHB was found to be restrained by the existence of catechin, and both i-PHB and s-PHB are miscible with catechin in the amorphous phase due to the intermolecular hydrogen-bonding. The effect of different stereochemical structures of i-PHB and s-PHB on the PHB-catechin interaction has been discussed.