news of the week MAY 19, 2014 EDITED BY WILLIAM G. SCHULZ & SOPHIA L. CAI
THERMOSETS BUILT TO BREAK DOWN
poly(hexahydrotriazine) is even stronger and is resistant to solvents and cracking from environmental stress. “There aren’t a lot of new polymer-forming reactions,” Hedrick points out. Thermosets made via this new condensation, he says, have promising microelecPOLYMERS: Novel reaction tronic, automotive, and aerospace applications. “You creates strong plastics that can take the material back down to the monomer after can be unzipped with acid its useful lifetime,” he says. “That has huge ramifications. When you think about working on O a complex automotive or aerospace part, F PLASTICS HAD personalities, ther- H N the ability to rework and refabricate it if NH 2 2 mosets would have a reputation for you make a mistake is priceless.” 4,4´-Oxydianiline being strong and stubborn. Unlike ther“This is an elegant use of readily moplastics, which make up water bottles, available starting materials Paraformaldehyde, N-methylpyrrolidone (NMP) strawberry containers, and other recyand easy-to-do chemistry,” clable plastics, thermosets can’t be recomments Stuart J. Rowan, a molded with heat or chemicals. polymer expert at Case Western N Once hardened, a thermoset is Reserve University. “Given the simN O locked into its shape because of plicity of the reaction conditions chemical crossand the wide variety of amine-containing linking. This monomers that are commercially available, one makes thermosets can imagine using this chemistry to obtain a wide O N useful in applicarange of interesting materials.” Indeed, the IBM reH N tions where the plastic • NMP searchers show they can make organogels O will encounter high temwith self-healing properties using the same H N peratures or harsh chemicals reaction on a different diamine monomer. but also means thermosets can’t García tells C&EN that she disbe recycled. So they ultimately covered the polymerization wind up in landfills. when she was trying to make a Hemiaminal dynamic Now, thanks to a new polyknown thermoset material and O covalent network merization reaction, chemists accidentally left out one of the have made thermosets that can starting materials. What she got was a be returned to their constituent plastic plug at the bottom of her reaction flask. N diamine monomers via exposure to low pH (Science “I had to break the flask with a hammer to get 2014, DOI: 10.1126/science.1251484). it out,” she recalls. Once out, she couldn’t grind A team led by Jeannette M. García and James L. Hed- Heat the polymer up, so she took a hammer to it too. rick of the IBM Almaden Research “Since we were after high-strength materials anyCenter developed the reaction, way, I decided to go ahead and try to figure out what N which condenses a diamine monoexactly I’d made.” With help from the computational mer with paraformaldehyde. At chemists at IBM, García figured out that she had preO low temperature, the reaction forms pared a poly(hexahydrotriazine). a hemiaminal dynamic covalent network. In developing the thermosets, the group was conTurn up the heat, and this material will cycerned with costs. The 4,4ʹ-oxydianiline is inexpensive clize to form a poly(hexahydrotriazine). and commercially available. Also, García says, “there’s N To make the thermosets, the researchers use no catalyst involved in the 4,4ʹ-oxydianiline—a common monopolymerization, so you don’t N N N mer used to make polyimides, such have to worry about metal as DuPont’s Kapton. With this dicontamination and you don’t O amine, the hemiaminal network is O have to worry about purification of as strong as fiberboard, despite your product. That keeps costs down.” Poly(hexahydrotriazine) the fact that almost one-third IBM hopes to partner with a of the material is composed chemical maker to develop New polymerization leads to two of water and N-methylpyrthe materials further.— different types of material, depending N rolidone solvent. The resulting on the reaction temperature. BETHANY HALFORD ARI ENTIN/IBM
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García (left) and Hedrick.
CEN.ACS.ORG
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MAY 19, 2014
