by Jackie Swift
“Plastics are ubiquitous in our environment,” says Erin E. Stache, Cornell University Presidential Postdoctoral Fellow. “We use them in just about everything: in our water bottles, our coffee cups, the cars we drive. They’re an important part of our everyday life. And so the synthesis of these materials and how we go about making them is very important.”
Stache has come to Cornell to work with Brett P. Fors and Geoffrey W. Coates, Chemistry and Chemical Biology, on new techniques for creating plastics.
Plastic is a type of polymer, consisting of many repeating smaller molecules called monomers. “As you string the monomers together, the polymer begins to grow and you make a macromolecule,” Stache explains. “This macromolecule starts to take on new properties different from the properties of the monomers. By controlling the sequence of the monomer you’re using and the size of the polymer, you can begin to dictate the function that the resulting material will have.”
Making New Thermoplastics for the Automotive and Aerospace Industries
Stache collaborates with Fors and Coates to take two different polymer synthesis techniques, each favored by one of the researchers, and combine them in a new manner to create new types of polyketones, hard thermoplastics that are used in the automotive and aerospace industries. With the Coates group, Stache uses transition metal catalysis to control the sequence of monomers. The Coates group is known for using this method to string monomers like epoxides and anhydrides together in an alternating fashion to give specific properties to the final material.
With the Fors group, Stache uses visible light to control the polymer sequence. The Fors group is pioneering this approach, which gives spatial and temporal control over the polymer. Wherever the researchers shine the light, the polymer there begins to grow. As they turn the light on and off, they dictate when the growth begins and ends.
“You have really tight control over the sequence using visible light,” Stache says. “That’s really important for the properties and things you want to build. Typically, these polymers are created thermally, but if we use visible light, we can think about patterning them off the surface, making polymer brush architectures, for instance.” Polymer brush architectures can be used for such industrial applications as stabilizing colloid gels and emulsions or reducing friction between surfaces.
New Methods from Existing Techniques
These catalysis techniques are not completely new to Stache. As a graduate student at Colorado State University and a visiting student at Princeton, she worked on the catalysis of small molecules (those with a molecular weight of 900 Daltons or lower), using transition metal catalysis such as the Coates group’s technique and photoredox catalysis similar to the Fors group’s technique. Now, at Cornell, she looks forward to learning how to apply these techniques to create large molecule polyketones.
“Polyketones have traditionally been made using a different palladium catalyzed method,” she says. “But based on the mechanism of polymerization that exists right now, it’s hard to incorporate different types of monomers. We think we can use transition metal catalysis with visible light. We’ll access a new mechanism of polymerization that will give us a path to a more diverse set of these polyketones. It’s exciting to think we can take these simple structures, these monomers, and use these methods, which were first developed in small molecule chemistry, to create something new.”
Plastics: An Environmental and Societal Challenge
Along with creating new polymer materials, Stache wants to address environmental issues stemming from plastics. “There’s a looming crisis of polymer buildup coming,” she says. “Plastics like polyethylene and polypropylene are great materials; we use them for everything. But the problem is their strong properties, which make them so great for so many applications, also mean they don’t degrade. They are filling our landfills, and right now there’s an island of plastic garbage growing in the Pacific Ocean. We have to do something about that.”
“The polymer chemists in the Coates group, especially, are trying to build new materials that have similar properties to polyethylene and polypropylene, but that can actually degrade.”
Stache found her environmental concerns coincide with Fors’ and Coates’ interests. Both researchers want to make bio-renewable polymers that can address the environmental issues. “The polymer chemists in the Coates group, especially, are trying to build new materials that have similar properties to polyethylene and polypropylene, but that can actually degrade,” Stache says. “These new materials could hopefully start to replace the non-biorenewable, non-biodegradable polymers.” She hopes to incorporate that environmental approach into her own work. In particular she wants to create the new forms of polyketones from monomers that come from biorenewable sources.
“I think chemical science is a puzzle,” she says. “We start putting pieces together and see what picture takes shape. But for me, the puzzle had to serve a bigger purpose. So tackling these societal, environmental challenges of dealing with polymers, that’s really rewarding. That’s what I’m looking forward to. That’s the opportunity we have here at Cornell, to think of really creative solutions to these really important challenges. Having this fellowship gives me the freedom to look out there and ask, ‘What are the challenges? What are some really creative and ambitious approaches we can take to this?’ And then see what we come up with.”