Iminodiacetic acid enhances the mechanical and degradation properties of copolyesters by hydrogen bonding and branching

The development of biodegradable polyester materials is of great significance in alleviating the problem of plastic pollution. Poly(butylene terephthalate adipate) (PBAT) is a typical aliphatic-aromatic copolyester and has a capacity of several hundred thousand tons per year. However, the relatively low mechanical strength and high requirement for degradation environment of PBAT limit its application fields. To compensate for the deficiencies in mechanical and degradable properties of PBAT, this study reports a molecular chain structure design on the amorphous region using diethyl iminodiacetate (DEI). A series of poly(butylene adipate iminodiacetate terephthalate) (PBAIT) with a DEI content of 5–20 mol% were obtained. DEI contains secondary amine groups, which can be amidated with ester bonds to produce branched sites, and branched structures can be formed from 75 to 79 % of DEI during the copolymerization process. PBAIT-10 exhibit better tensile strength (23.87 MPa), tensile modulus (108.2 MPa) and hydrophilicity than those of PBAT. In addition, PBAIT-10 also shows very high toughness, with an elongation at break of over 1000 %. PBAITs can be degraded in enzymatic or hydrolytic environments. The degradation mechanism was analyzed by ¹H NMR spectra and FTIR, and further combined with 2D-IR analysis, which reveals the rapid degradation of the BI chain segments regardless of whether or not they form branched sites. This work provides an idea to prepare copolyesters that combine good mechanical properties with degradability under mild conditions.