High-Barrier-Property Copolyesters Based on Spiroglycol with Controlled Degradation

Finding a balance between thermo-mechanical properties and degradation properties is important for degradable polyesters to dissolve, addressing environmental problems. In this work, spiroglycol, an acetal monomer with symmetrical rigid spirocycles which can effectively increase the glass transition temperature (Tg) of polymers and easily hydrolyze in acidic environments, was introduced into poly(ethylene succinate) (PES) to synthesize poly(ethylene succinate-co-spirocyclic succinate) (PESS) copolyesters with contents ranging from 10 to 80 mol % spiroglycol units via melt polycondensation. As the spiroglycol unit content increases, the Tg, thermal resistance, and mechanical and barrier properties of the PESS copolyesters were obviously improved. Specifically, the glass transition temperature of PESS50 was enhanced up to 33.2 °C and it had a tensile modulus of 1398 MPa and tensile strength of 20.2 MPa, with an elongation at break of 333.4%. In addition, the barrier properties of PESS50 are significantly higher compared to PBAT and can achieve the purpose of food freshness preservation. The acidic cleavage of the spiroglycol unit can be accomplished in an acidic environment, while the ester bond can be hydrolyzed in an enzyme environment, achieving the goal of controlled degradation. As a result, while ensuring a certain degree of degradation performance, the thermo-mechanical properties have been improved.