SYNTHESIS, CHARACTERIZATION, AND IN-VITRO DEGRADATION OF A NOVEL THERMOTROPIC TERNARY COPOLYESTER BASED ON P-HYDROXYBENZOIC ACID, GLYCOLIC ACID, AND P-HYDROXYCINNAMIC ACID

The direct copolycondensation of aromatic hydroxy acid with aliphatic alpha-hydroxy acid was achieved by using certain amounts of a third co monomer with or without a catalyst. High molecular weight main-chain t hermotropic liquid crystalline terpolyesters with a potentially biodeg radable property based on p-hydroxybenzoic acid (PHBA), glycolic acid (GA), and the bridge comonomer trans-p-hydroxycinnamic acid (PHCA) wer e synthesized via a one-step melt copolycondensation process. Solution viscosity, Fourier transform infrared spectrometer (FTIR), and nuclea r magnetic resonance (H-1 NMR, C-13 NMR) measurements were used to ide ntify the formation and structure of this terpolymer; a random sequenc e distribution of the comonomeric units along the polymeric chains was concluded. A single glass transition temperature at about 82 degrees C and a broad endothermic transition with a maximum at 150 degrees C w ere discerned in the DSC profiles of the as-prepared polymers. Wide-an gle X-ray diffraction (WAXD) analysis indicated the occurrence of a ne matic structure in the as-injected fiber of the terpolymer. This nemat ic liquid crystallinity was further confirmed from the characteristic textures under optical polarizing microscopy (POM): a Schlieren-type t exture for low molecular weight copolymers or banded textures for high molecular weight ones over a wide temperature range. The anisotropic- isotropic transition was not clearly detectable until the polymer deco mposition. The in vitro degradation of the thermotropic liquid crystal line ternary copolyester was evaluated by water absorption, inherent v iscosity, morphology, and thermal properties after treatment in buffer media in the absence of enzyme. It is clearly shown that the hydrophi licity was greatly improved due to the incorporation of GA segments. T he copolymer degraded via a simple hydrolysis of the ester bonds of GA -rich segments, and the aromatic counterpart could also be involved in the hydrolysis. These degradations occurred predominantly in the amor phous or less aligned