Melt polycondensation of poly (butylene oxalate-co-succinate) with great potential in curbing marine plastic pollution

Marine plastic pollution, with annual emissions into the marine over 53 million metric tons, has been a major worldwide concern. Many of so-called "biodegradable" polymers degrade very slowly in seawater. Oxalate have attracted attention because the electron-withdrawing effect of adjacent ester bonds promotes their natural hydrolysis, particularly in the ocean. However, the low boiling point and poor thermal stability of oxalic acids severely limits their applications. The successful synthesis of light-colored poly(butylene oxalate-co-succinate) (PBOS), with weight average molecular weight higher than 1 × 105 g/mol, displays the breakthroughs in the melt polycondensation of oxalic acid-based copolyesters. The copolymerization of oxalic acid retains the crystallization rate of PBS, with minimum half-crystallization times from 16 s (PBO10S) to 48 s (PBO30S). PBO10S-PBO40S exhibit good mechanical properties with elastic modulus of 218-454 MPa, and tensile strength between 12 and 29 MPa, better than packaging materials such as biodegradable PBAT and non-degradable LLDPE. PBOS achieve rapid degradation in the marine environment, with a mass loss 8%- 45% after 35 days. The characterization of structural changes demonstrate that the introduced oxalic acid plays a key role in the process of seawater degradation. This new class of polymers therefore provide highly promising materials for sustainable packaging with unique seawater degradation properties.