Morphology, phase behavior, and relaxation processes in a series of aromatic-aliphatic thermotropic polymer biomaterials
Résumé
This investigation describes the phase behavior, morphology, and molecular relaxation behaviors observed in a series of random aromatic-aliphatic thermotropic copolyesters derived from the synthesis of p-hydroxybenzoic acid (HBA), vanillic acid (VA), 4,4′-sulfonylbis(2-methylphenol) (dBPS), and adipic acid (AD). The polymers vary in the ratio of mesogenic to nonmesogenic units. Material thermal properties, including the glass-transition temperatures and liquid-crystalline stability, were determined by differential scanning calorimetry and hot-stage optical microscopy. Wide-angle X-ray diffraction intensity profiles highlight that the materials possess a nematic chain registry. Solid-state wide-line 1H NMR T1 and T 1ρ spin-lattice relaxation measurements have been used to evaluate both the homogeneity of the polymer morphologies and molecular motions. Dynamic mechanical analysis demonstrates that the polymers show three common relaxation processes in tan δ in the temperature range from -120 to 150 C. Four independent relaxations have been identified using the different techniques which have been attributed to molecular group motions associated with the individual moieties.