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Hydrogen-bonded aromatic–aliphatic polyester–amides (PEAs) were prepared by solution/melt polycondensation of aromatic–aliphatic amidodiols 1,4-bis(4-hydroxybutyramide)benzene (BHBB), 1,4-bis(5-hydroxy pentamide)benzene, 1,4-bis(6-hydroxyhexamide)benzene, 1,4-bis(4-hydroxybutyramidexylene), 1,4-bis(5-hydroxypentamidexylene, 1,4-bis(4-hydroxybutyramide)benzene, and 1,4-bis(6-hydroxyhexamidexylene) with terephthaloyl chloride/dimethyl terephthalate. Aromatic–aliphatic amido diols were prepared by the aminolysis of γ-butyrolactone, δ-valerolactone, and ε-caprolactone with aromatic diamines such as paraphenylene diamine and paraxylene diamine. The monomers and polymers were characterized by chemical analysis (hydroxyl value and elemental analysis), Fourier transform infrared spectroscopy, ¹H NMR, and ¹³C NMR. The thermal- and phase-transition behaviors of the polymers were investigated by differential scanning calorimetry in combination with hot-stage optical microscopy. Crystallinity of polymers was examined with wide-angle X-ray diffraction. The polymers exhibited liquid crystallinity with layered structures formed by self-organization of the hetero intermolecular hydrogen-bonded networks indicating smectic phases except for PEAs prepared from BHBB. The hydrogen atom of the phenyl-substituent group forces the neighboring carbonyl groups out of plane of the rings preventing formation of layered structures in the case of BHBB. The PEAs retained intermolecular hydrogen bonding even in the mesomorphic state, and variations in the hydrogen-bonded lamellae/micelles might be responsible for the variations from one smectic to another texture. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 335–346, 2003

Melt-processable liquid-crystalline terpolyesters of 4-hydroxyphenylacetic acid (HPAA) and 3-(4-hydroxyphenyl)propionic acid (HPPA) with terephthalic acid and 2,6-naphthalene diol were synthesized by one-step acidolysis melt polycondensation followed by postpolymerization and were characterized with viscosity studies, Fourier transform infrared (FTIR) and NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarized light microscopy, and wide-angle X-ray diffraction. The melting behaviors and liquid-crystalline transition temperatures of the terpolyesters were dependent on the composition of the HPAA/HPPA content. The transition temperatures of the polyesters could be effectively reduced by the introduction of an even number of built-in short methylene spacers in combination with the 2,6-naphthalene offset structure. A terpolyester with an HPPA content of 33% (NTP33) showed optimum properties for the glass-transition temperature, around 71 °C, and the melting temperature, near 240 °C, with a Schlieren nematic texture. The polymer showed excellent flow behavior in a Brabender plasticorder. It was also thermally stable up to 400 °C. NTP33 showed 2.5% in vitro hydrolytic degradation in buffer solutions of pH 10 at 60 °C after 540 h. Considerable enzymatic degradation was also observed with porcine pancreas lipase/buffer solutions in comparison with Candida rugosa lipase after 60 days. The degradation was also followed with FTIR, DSC, and TGA. Apart from the temperature and pH of the buffer solution, several structural parameters, such as the aromatic content, crystallinity percentage, and composition of the polymer, affected the degradation behavior. FTIR studies indicated the involvement of chain scission during degradation. Scanning electron microscopy studies further showed that surface erosion also played a major role in the degradation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1845–1857, 2002

The homopolyester of 4-hydroxyphenylacetic acid (HPAA) was synthesized by one-pot, slurry-melt, and acidolysis melt polymerization techniques and was characterized by its inherent viscosity and IR and NMR spectra. Differential scanning calorimetry (DSC), polarizing light microscopy (PLM), and wide-angle X-ray diffraction (WAXD) studies of the homopolymer were carried out for its thermal and phase behavior. The results indicated that the yield and molecular weight of the polymer depended on the method of preparation; moreover, the acidolysis melt polymerization of the pure acetoxy derivative of HPAA was the best method for the preparation of high molecular weight poly(4-oxyphenylacetate) (polyHPAA) without side reactions. DSC and PLM studies also showed that the thermal and optical properties depended largely on the polymerization conditions and inherent viscosity values. PolyHPAA did not show a clear texture typical of liquid-crystalline polymers, whereas after cooling from the melt, structures similar to spherulitic crystals were observed. WAXD patterns showed a crystalline nature. The in vitro degradability of the polymer was also studied via the water absorption in buffer solutions of pH 7 and 10 at 30 and 60 °C; this was followed by Fourier transform infrared, inherent viscosity, DSC, thermogravimetric analysis, WAXD, and scanning electron microscopy techniques. Unlike Vectra®, which showed no degradation, polyHPAA showed an increase in hydrolytic degradation from 5.0 and 6.0% at 30 °C to 12.5 and 15.0% at 60 °C after 350 h in buffer solutions of pH 7 and 10, respectively. The results indicated a possible biomedical prosthetic application of poly(oxyphenylalkanoate)s such as polyHPAA with better crystallinity coupled with degradability as a substitute for poly(hydroxyalkanoates). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2430–2443, 2001

Hydrolytically degradable copolyesters of the naturally occurring monomer 4-hydroxyphenylacetic acid (HPAA) with 4-hydroxybenzoic acid (HBA) were synthesized for the first time by the acidolysis melt polymerization of their acetoxy derivatives. The HPAA/HBA copolyesters prepared by acidolysis melt polycondensation had higher yields and molecular weights than those obtained by a one-pot method. The high-temperature solvent Dowtherm® improved the color of the polyester. Although catalysts did not affect the inherent viscosity and yield of the polymer, they did reduce the polymerization time. A higher degree of polymerization was achieved with postpolymerization and annealing techniques. Copolyesters prepared in different molar ratios were analyzed by elemental analysis, IR, NMR, and inherent viscosity and were further characterized for their thermal and phase properties by thermogravimetric analysis, differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy. The composition of the copolyesters affected the yield, solubility, and inherent viscosity. The NMR data indicated comparatively high randomization for the copolyester obtained by acidolysis melt polymerization. The 60/40 HPAA/HBA copolyester formed a birefringent melt with a grainy texture above 175 °C with isotropization at 297 °C and thermal stability above 350 °C. The occurrence of birefringence with a grainy texture in the melt indicates a layered smectic phase; this was supported by wide-angle X-ray diffraction powder patterns. The in vitro hydrolytic degradability of the copolyester was studied by the measurement of the water absorption of the film samples in buffer solutions of pH 7 and 10 at 30 and 60 °C. The copolyester showed considerable hydrolytic degradation, enough to be called biodegradable, compared with the commercial polyester Vectra®, thereby demonstrating prospects for syntheses of copolyesters with tailor-made degradability. The degradation of the copolyester was identified by Fourier transform infrared, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy. These polyesters with controlled crystallinity and degradability should be considered for possible applications in biomedical areas (e.g., bone fixation devices in fracture treatment) in which high strength with biodegradability is an essential requirement. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 693–705, 2001