‘Infinitely’ Recyclable Polymer Has Practical Properties of Plastics

Polymers are a broad class of materials characterized by long chains of chemically bonded, repeating molecular units called monomers. Synthetic polymers today include plastics, as well as fibers, ceramics, rubbers, coatings, and many other commercial products.
Building on fundamental knowledge

The work builds on a previous generation of a chemically recyclable polymer Chen’s lab first demonstrated in 2015. Making the old version required extremely cold conditions that would have limited its industrial potential. The previous polymer also had low heat resistance and molecular weight, and, while plastic-like, was relatively soft.

But the fundamental knowledge gained from that study was invaluable, Chen said. It led to a design principle for developing future-generation polymers that not only are chemically recyclable, but also exhibit robust practical properties.

 

Eugene Chen, professor of chemistry

Credit:  CSU

The new, much-improved polymer structure resolves the issues of the first-generation material. The monomer can be conveniently polymerized under environmentally friendly, industrially realistic conditions: solvent-free, at room temperature, with just a few minutes of reaction time and only a trace amount of catalyst. The resulting material has a high molecular weight, thermal stability and crystallinity, and mechanical properties that perform very much like a plastic. 

 

Most importantly, the polymer can be recycled back to its original, monomeric state under mild lab conditions, using a catalyst. Without need for further purification, the monomer can be re-polymerized, thus establishing what Chen calls a circular materials life cycle.

This piece of innovative chemistry has Chen and his colleagues excited for a future in which new, green plastics, rather than surviving in landfills and oceans for millions of years, can be simply placed in a reactor and, in chemical parlance, de-polymerized to recover their value – not possible for today’s petroleum plastics. Back at its chemical starting point, the material could be used over and over again – completely redefining what it means to “recycle.”

“The polymers can be chemically recycled and reused, in principle, infinitely,” Chen said.
Next steps

Chen stresses that the new polymer technology has only been demonstrated at the academic lab scale. There is still much work to be done to perfect the patent-pending monomer and polymer production processes he and colleagues have invented.

With the help of a seed grant from CSU Ventures, the chemists are optimizing their monomer synthesis process and developing new, even more cost-effective routes to such polymers. They’re also working on scalability issues on their monomer-polymer-monomer recycling setup, while further researching new chemical structures for even better recyclable materials.

“It would be our dream to see this chemically recyclable polymer technology materialize in the marketplace,” Chen said.

The paper’s first author is CSU research scientist Jian-Bo Zhu. Co-authors are graduate students Eli Watson and Jing Tang.

Chen’s co-authors, from left: Research scientist Jian-Bo Zhu, and graduate students Jing Tang and Eli Watson.

Credit: CSU

Contacts and sources:
Anne Manning 

Colorado State University (CSU)

Citation:  A synthetic polymer system with repeatable chemical recyclability.
Jian-Bo Zhu, Eli M. Watson, Jing Tang, Eugene Y.-X. Chen. Science, 2018; 360 (6387): 398 DOI: 10.1126/science.aar5498