Structural and Thermal Characterization of Bluepha® Biopolyesters: Insights into Molecular Architecture and Potential Applications

This study presents an in-depth molecular and structural characterization of novel biopolyesters developed under the trademark Bluepha^®. The primary aim was to elucidate the relationship between chemical structure, chain architecture, and material properties of these biopolyesters to define their potential applications across various sectors. Proton nuclear magnetic resonance (¹H NMR) analysis identified the biopolyesters as poly[(<i>R</i>)-3-hydroxybutyrate-<i>co</i>-(<i>R</i>)-3-hydroxyhexanoate] (PHBH) copolymers, containing 4% and 10% molar content of hydroxyhexanoate (HH) units, respectively. Mass spectrometry analysis of PHBH oligomers, produced via controlled thermal degradation, further confirmed the chemical structure and molecular architecture of the PHBH samples. Additionally, multistage electrospray ionization mass spectrometry (ESI-MS/MS) provided insights into the chemical homogeneity and arrangement of comonomer units within the copolyester chains, revealing a random distribution of hydroxyhexanoate (HH) and hydroxybutyrate (HB) units along the PHBH chains. X-ray diffraction (XRD) patterns demonstrated partial crystallinity in the PHBH samples. The thermal properties, including glass transition temperature (<i>T_g</i>), melting temperature (<i>T_m</i>), and melting enthalpy (Δ<i>H_m</i>), were found to be lower in PHBH than in poly(<i>R</i>)-3-hydroxybutyrate (PHB), suggesting a broader application potential for the tested PHBH biopolyesters.