Conventional plastics are difficult to recycle because end-of-life processing generally is either energy-intensive or alters the physical properties of the materials. A team of researchers from the Lawrence Berkeley National Laboratory (Berkeley, Calif.; www.lbl.gov) and the University of California at Berkeley (www.berkeley.edu) is developing polymers that can be de-polymerized using acids at ambient temperatures. Known as poly-diketoenamines (PDKs), the materials are made through condensation reactions between ß-triketones and amines, and could allow plastics that can be re-manufactured inexpensively and without a loss of performance.
PDKs are prepared by reacting ß-triketones with either aliphatic or aromatic amines to form dynamic covalent diketoenamine bonds. “The reaction between triketones and amines is spontaneous at ambient temperature,” says LBNL research leader Brett Helms, “but can also be conducted in a ball-mill, in the melt, or in solution. It requires no additional chemicals or catalysts,” he says.
The resulting polymers can be depolymerized by treating with strong aqueous acids (either H2SO4 or HCl) at ambient temperature to yield triketone and amine monomers at greater than 90% yields.
Helms say PDKs can be formulated to access a broad range of physical properties. “It’s likely that they are most similar to polyamides and polyurethanes,” he notes.
The triketone monomers can be synthesized in a single step from 1,3-dione and polytopic carboxylate compounds, which are both are widely available from petrochemicals processing, but increasingly also from bio-based sources.