[Lectures] Design Tomorrow’s Polymers with Biodegradability and Chemical Recyclability

  【Speaker】Dr. Xiaoyan Tang
                  Colorado State University
 
  【Time】 15:00 2020-1-14

  【Venue】 Room 234, Huaxue 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.