“Every monomer that goes in gives off a puff of light. The light is induced by a laser, and the puff of light has a color. In our case, it’s either green or yellow. By seeing whether it’s yellow or green, we see what monomer goes in.”Peng Chen, Cornell University
Synthetic polymers are everywhere in our society – from nylon and polyester clothing to Teflon cookware and epoxy glue. At the molecular level, these polymers’ molecules are made of long chains of monomer building blocks.
While the monomer sequence plays a critical role in a polymer’s properties, scientists have until now lacked a method for sequencing synthetic copolymers, which consist of different types of monomers in the same chain.
This has changed with the development of CREATS (Coupled REaction Approach Toward Super-resolution imaging) by Peng Chen, professor of chemistry at Cornell University, and his colleagues. Using CREATS, Chen and his colleagues can image polymerization catalysis reactions at single-monomer resolution and, through fluorescent signaling, differentiate monomers from one another. Both are important steps in discovering the molecular composition of a synthetic polymer.
They report this new technique, and the first discoveries they’ve made with it, in a paper in Nature Chemistry. The co-lead authors are Rong Ye, Xiangcheng Sun and Xianwen Mao, all former postdoctoral researchers in the Chen group. Other co-authors are former Chen group postdoctoral researchers Susil Baral and Chunming Liu, current postdoctoral researcher Felix Alfonso, and Geoffrey Coates, a professor in chemistry and chemical biology.
“Synthetic polymers are made of monomer units linked together like a string of beads,” said Chen. In the simplest polymers, the monomers are identical, but more complex properties arise when polymers contain monomers of different sorts – called copolymers. The precise arrangement of the monomers in a copolymer plays an important role in determining its properties, such as stiffness or flexibility.
Sequence plays a role in the properties of natural polymers, too. A protein, for example, is made of 20 amino acid monomers arranged in a very specific sequence.
“In a natural polymer, nature has control,” Chen said. “In synthetic polymers, humans are making the arrangements, and the chemists generally don’t have that precise control.”
Sequencing copolymers is difficult in large part because of the heterogeneity of synthetic polymers. Individual chains differ in length, composition and sequence, which requires single-polymer sequencing methods that can resolve and identify individual monomers.
Some modern methods allow scientists to control the arrangement of monomers in a chain, Chen said, but only for very short polymers – 10 to 20 monomers long.
Using CREATS, the researchers can determine the sequence of a polymer as it is made, one monomer at a time, by imaging and identifying every single monomer as it is added to the polymer. To make the monomers visible, CREATS couples the polymerization reaction with another reaction that produces fluorescent signals.
“Every monomer that goes in gives off a puff of light,” Chen said. “The light is induced by a laser, and the puff of light has a color. In our case, it’s either green or yellow. By seeing whether it’s yellow or green, we see what monomer goes in.”
Chen’s group is already equipped to measure synthetic polymer properties. Now that they can determine the sequence of an individual polymer, a next step is to combine the two experiments to correlate structure and function, ultimately providing guiding principles for the design of polymers with specific properties.
“If you know how sequence controls property, you can really think about designing whatever sequence you want to achieve a certain property,” Chen said. “This knowledge presumably can help people tailor their materials for a desired application.”
This story is adapted from material from Cornell University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.