The accumulation of postconsumer plastic waste has brought severe consequences to the environment and human health. Among them, petroleum-based plastics are inert and may last for centuries after being discarded. Biodegradable polymers can degrade in laboratories or industrial compost settings, but there are growing concerns about their degradability in the real world, especially in seawater or landfill, where no specific conditions such as microbes, enzymes, or proper temperature and pH values are presented. Plastics recycling and degradation still rely on laborious activities from collecting and sorting to a variety of processes like incineration, mechanical recycling, and chemical recycling. For decades, a stream of research efforts has chased the dream to develop environmentally self-degradable plastics that automatically disappear in natural environment, without leaving behind fragments or harmful products. Ideally, the degradation of discarded polymers should complete under natural conditions, without any additional process, in a reasonable time frame. The pressure to the environment will be minimized if the degradation produces no harmful degradants or microplastics, or more favorably, generates the original monomer units or value-added upcycling products with good atom economy.
In this study, Luo and collaborators use poly(deca-4,6-diynedioic acid), or PDDA, a soluble polydiacetylene with short carboxyl side chains, as a model conjugate polymer to approach such an ideal degradation. When we put a piece of PDDA film into water, the soaked polymer film disintegrated into small pieces rapidly when standing on an outdoor shelf, and finally disappeared within one week. PDDA can be completely decomposed by sunlight in air, with a dominant green upcycling product of succinic acid, representing an ideal paradigm for the degradation and upcycling of conjugated polymers. Further study clearly demonstrated that PDDA undergoes a photo-oxidative degradation upon sunlight irradiation in air and 2-ketoglutaric acid should be a key intermediate, which is then decarboxylated and oxidized to the final product succinic acid.
In conclusion, this work represent a pioneering paradigm of environmentally degradable conjugated polymers, the complete degradation of PDDA into green upcycling products by sunlight in air also validates a promising universal strategy to degrade postconsumer conjugated polymers in natural environment.
The above research work was published in the Journal of the American Chemical Society on JUNE 28. Sidan Tian and Qiang Yue contributed equally to this work as first authors. Corresponding authors are Prof. Tang Ben Zhong from Hong Kong University of Science & Technology and Prof. Luo Liang from Huazhong University of Science and Technology.
URL：https://pubs.acs.org/doi/10.1021/jacs.1c04611
