Achieving Closed‐Loop Recycling of a Semi‐Conjugated Polymer through Incorporation of Ester Linkers

Design strategies to achieve degradation and ideally closed‐loop recycling of organic semiconductors have attracted great interest in order to minimize the electronic waste (E‐waste). In this work, three ester‐incorporated monomers were synthesized by the names of Thiophene‐Ester‐Ethylene‐Thiophene (TEET), Thiophene‐Ester‐Methylene‐Thiophene (TEMT), and Thiophene‐Ester‐Thiophene (TET), which were co‐polymerized via Stille polycondensation with a benzodithiophene (BnDT) pi‐conjugated unit to yield a series of ester‐incorporated polymers: PBnDT‐TEET, PBnDT‐TEMT, and PBnDT‐TET. While the ester‐only linker can maintain some extended conjugation in PBnDT‐TET, the other two ester linkers having conjugation breaking units result in isolated conjugated segments in PBnDT‐TEET and PBnDT‐TEMT, evidenced by UV‐Vis and CV results. This yields an improved photovoltaic performance of PBnDT‐TET compared to PBnDT‐TEET. While all three polymers can degrade under methanolysis, the alternating co‐polymer PBnDT‐TEET demonstrates the highest recyclability potential with a single dimethyl ester‐functionalized product with an excellent 92% isolated yield, which can then be repolymerized to obtain the repolymerized PBnDT‐TEET with a 36% yield. This work provides a framework towards achieving recyclable organic semiconductors to reduce E‐waste. Although the incorporation of ester linkers allowed for closed‐loop recycling, the low solar cell efficiency of PBnDT‐TEET highlights the significant challenges in achieving both recycling and high device performance.