Acid-Triggered, Degradable and High Strength-Toughness Copolyesters : Comprehensive Experimental and Theoretical Study

With the acceleration of the commercialization of degradable polymers, their poor mechanical properties continuously limit their applications. It is important to find a balance between the degradable properties and mechanical properties. Herein, poly(butylene terephthalate) (PBT) modified by SPG from 10% to 40 mol% were synthesized through a two-step polycondensation. Chemical structures, thermal properties, mechanical properties, viscoelastic behavior and degradation of poly(butylene terephthalate-co-spirocyclic terephthalate) (PBST) were investigated. The SPG could toughen the copolyesters and the elongation at break of PBST20 was up to 260%. Moreover, the introduction of SPG enables to hold an acid-triggered unit in the main chain. PBSTs copolymers maintain stable structures in a neutral environment, and the degradation under acid conditions will be unlocked. As tailoring the content of SPG, the degradable rate of the chain scission in response to acid stimuli will be adjusted. The acid degradation was proved to be occurred at the SPG units in the amorphous phase by DSC, XRD, GPC and 1 H NMR tests. After the acid degradation, the hydrolysis rate will also be accelerated, adapting to the requirements of different degradation schedules. The plausible hydrolytic pathways and mechanisms were proposed based on Fukui function analysis and density functional theory (DFT) calculation