Design Of High-Barrier And Environmentally Degradable Fdca-Based Copolyesters: Experimental And Theoretical Investigation

The 2,5-furandicarboxylic acid (FDCA)-based aliphatic-aromatic copolyester is an intensively researched area of bio-based polymers with high gas barrier and mechanical properties. However, the contradiction between the barrier and degradation performance still remains a huge challenge and severely limits their applications. Here, we combine branched neopentyl glycol, hydrophilic diglycolic acid, and FDCA to prepare poly(neopentyl glycol diglycolate/furandicarboxylate) (PNDF) copolyesters. With poor crystallization capability, PNDF40 and 50 (content of NF units) display low modulus (58 vs 108 MPa) but elastomeric behavior. Their tensile broken samples can even rapidly restore the original length, which might be derived from the physical crosslinking networks. It was interesting to find that even when more than 50% of the NF units were replaced by ND units, the PNDF copolyesters still retained high gas barrier. The introduction of diglycolic acid improved the hydrolysis rate, showing potential degradability under environmental conditions. However, enzymatic degradation using Candida antarctica lipase B (CALB) revealed that the branched neopentyl glycol decreased the biodegradation rate when compared with other linear diols. Furthermore, the hydrolytic pathway of PNDF was explored by density functional theory (DFT) calculation. Through Fukui function analysis, we identified the most active sites of PNDF for hydrolysis. Additionally, the calculated energy barrier indicated that hydrolysis of the polymer chain became easier with the increase in the number of ND units. Molecular dynamics (MD) simulations of PNDF-CALB illustrated that Val154 and Gln157 of CALB located at catalytic entrance formed noncovalent interaction with PNDF, which would sterically hinder the carbonyl carbon from reaching an ideal distance for nucleophilic attack and decrease the tendency to enter a pre-reaction state.