Controlling the Marine Biodegradability of Poly(butylene succinate- <i>co</i> -adipate) by Chain Extension via Boronate Esters with Various Hydrolyzabilities

Controlling the biodegradation rate is essential for expanding the potential application range of biodegradable polymers. The incorporation of stimuli-responsive bonds (SRBs) in a polymer chain is an effective way to adjust the rate of the initial chain scission process prior to microbial assimilation. Herein, we report a facile modular strategy for controlling the marine biodegradation rate of a highly biodegradable polymer, poly(butylene succinate-co-adipate) (PBSA), by varying the responsiveness of the SRBs without varying their density. Short PBSA chains with boronic acid chain ends were synthesized. Chain extension was achieved by adding various commercially available tetraol linkers, forming boronate esters (BEs), which act as water-sensitive SRBs. The hydrolytic stability of the BE linkage in the polymer could be readily tuned through the choice of the tetraol linker, without the need to change the boronic acid-modified PBSA. While pristine PBSA was brittle and could not be mechanically tested, all the extended polymers displayed improved mechanical properties, with a strain at break of ca. 500% and a stress at break of ca. 20 MPa, regardless of the linker used. Meanwhile, the biodegradation rate in seawater was successfully varied: the biodegradation of unmodified PBSA started rapidly in less than 10 days, whereas the extended polymers showed delayed biodegradation that was directly correlated with the hydrolyzability of the BE. This study will help increasing the range of applications of biodegradable polymers and facilitating synthesis methods, which will benefit plastics of short, yet varying lifetime for applications such as packaging.