Title: Design Tomorrow’s Polymers with Biodegradability and Chemical Recyclability
Speaker: Research Scientist II Xiaoyan Tang, Colorado State University
Date: 2020-01-14 15:00 PM
Location: Room 234，Chemistry Building
Abstract：
Plastics are the most widely used man-made substances in modern life. However, the currently unsustainable practices in the production and the disposal of plastics continue to deplete out finite natural resources and create severe worldwide environmental consequences. Tackling these existing plastic waste problems requires efforts and great cooperation by all the key players, from plastic producers to recyclers, retailers and consumers. It is argued that the development of chemically recyclable and/or biodegradable polymers from biorenewable resources offers a feasible solution to solve the end-of-life issue of plastic waste and preserve our finite natural resources. In this context, we developed a series of completely recyclable polymers based on γ-butyrolactone (GBL). Among them, the ring-opening polymerization (ROP) of biorenewable bifunctional α-methylene-γ-butyrolactone (MBL) into degradable and recyclable polyester was investigated in detail: controlling vinyl-addition/ring-opening/cross-linking polymerization pathways. Moreover, poly(hydroxyalkanoate)s (PHAs), as a class of microbially produced polyesters, have gained attraction as suitable alternatives to commodity plastics due to their comparable physical properties to polyolefins and most importantly their unique ability to biodegrade in ambient environments, including oceans. Natural PHAs are isotactic polymers containing a chiral site in each repeating unit, and their properties span a wide range depending on the length of the side aliphatic chain on the b-carbon, implying their wide applications in biomedical, pharmaceutical, and packaging industries. However, currently high production costs and low production volumes of biologically produced PHAs largely limit their applications as commodity bioplastics. In the context of creating a synthetic equivalent of naturally produced PHAs, both high isotacticity and high molecular weight are typically required for practical use. Accordingly, we recently developed a catalyzed chemical synthesis route to highly isotactic biodegradable PHAs from ROP of racemic eight-membered cyclic diolides derived from bio-sourced succinate. We also developed a diastereoselective polymerization methodology enabled by catalysts that directly polymerize mixtures of eight-membered diolide monomers with varying starting ratios of chiral racemic (rac) and achiral meso diastereomers into stereo-sequenced crystalline PHAs with isotactic and syndiotactic stereo-diblock or stereo-tapered block microstructures. The material properties can be tuned by varying the catalyst and monomer structures and the ratio of starting rac/meso diastereomers.
Biography:
Dr. Xiaoyan Tang received her B.Sc. degree from Wuhan University in 2009. Then she joined Prof. Yuesheng Li’s group in Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, where she was trained on the synthesis and characterization of air-sensitive half-metallocenes for olefin coordination (co)polymerization. She went to Prof. Kotohiro Nomura’s group in Tokyo Metropolitan University as a visiting researcher, focusing on the synthesis of vanadium(V) complexes for olefin dimerization or (co)polymerization during her pursue of Ph.D. After graduation in 2015, she joined the group of Prof. Eugene Y.-X. Chen as a postdoctoral research fellow at Colorado State University, where she was promoted to Research Scientist II in 2018. Targeting at the fast-growing demand of plastics and world-wild pollution associated with tremendous annual consumption, she has been working on the development of novel and efficient organometallic and organic catalysts for the synthesis of biodegradable and/or chemically recyclable polymers.
