Synthesis, properties and biodegradation of periodic copolyesters composed of hydroxy acids, ethylene glycol, and terephthalic acid

Abstract

Aromatic polyesters such as poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT) and poly(butylene terephthalate) (PBT) are widely used all over the world due to their excellent physical properties. However, their degradation in the environment is very slow and the environmental load of their wastes is a potential problem. On the other hand, poly(l-lactic acid) (PLLA) and poly(glycolic acid) (PGA) have attracted attention for their biodegradability. We expected that periodic copolyesters composed of hydroxy acids, ethylene glycol, and terephthalic acid can be biodegradable polymer with relatively high melting points. In this study, a series of novel periodic copolyesters was synthesized and their physical properties and biodegradabilities were investigated. The 2:1 condensation products (LEL and GEG) of l-lactic acid (LA) or glycolic acid (GA) and ethylene glycol were synthesized from the reaction of potassium salt of LA or GA with 1,2-dibromoethane. Then, the polycondensation of LEL or GEG with chloride derivatives of dicarboxylic acids (terephthalic acid, 2,5-furandicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and adipic acid) were performed to produce a series of periodic copolyesters such as poly((ethylene diglycolate) terephthalate) (poly(GEGT)) and poly((ethylene di(l-lactate)) terephthalate) (poly(LELT)). The most of the copolyesters with LA units such as poly(LELT) were amorphous. In contrast, the copolyesters with GA units exhibited relatively high melting temperature (e.g. Tm = 209 °C for poly(GEGT)). The preliminary degradation tests of poly(GEGT) and poly(LELT) were performed. The obtained poly(GEGT) showed biodegradability in seawater at 27 °C.