The Hydrogen-Bonding Interactions between 4,4’-Thiodiphenol and Some Poly(hydroxyalkanoic acid)s Revealed by DSC and FT-IR Spectroscopic Analysis

Abstract

The specific intermolecular hydrogen-bonding interaction between some poly(hydroxyalkanoic acid)s (PHAs) and 4,4’-thiodiphenol (TDP) were studied by DSC and FT-IR. Chemosynthetic poly(3-hydroxypropionate), bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and bacterial poly(3-hydroxybutyrate- co-4-hydroxybutyrate) were used as the PHA samples. A curve-fitting program for line-shape analysis of FT-IR spectra was also applied to investigate the fractions of associated carbonyl groups. The measurements show there are strong intermolecular hydrogen bonds between the carbonyl groups of PHAs and the hydroxyl groups of TDP. The content of intermolecular hydrogen bonds is influenced by both the content of TDP in the PHA/TDP blends and the crystallizability of PHAs. The crystallizability is related to the flexibility of the molecular chains. With the addition of TDP to PHAs, the decrease of melting point Tm and the increase of glass transition temperature Tg of the component of PHAs in the blends were found. When the content of TDP was more than 40%, phase separation took place, which was so serious that Tg dropped obviously as soon as the content of TDP was up to 80%. At this time, it is difficult for the molecules of PHAs and TDP to form intermolecular hydrogen bonds. As indicated by the study of FT-IR, TDP has more ability to form the self-hydrogen-bond of TDP-HO···HO-TDP type than the inter-hydrogen-bond of PHA-C=O···HO-TDP type. Based on the analysis on the eutectic behavior in different PHA/TDP pairs, it was found that the bulkiness of the pendant alkyl groups in the chains of PHAs affects the eutectic behavior.