Cu(0) reversible deactivation radical polymerization (RDRP) has recently emerged as a powerful tool for the polymerization of diverse kinds of vinyl monomers using copper metal as catalyst. This technique has provided access to abundant materials with low dispersity using a simple and inexpensive setup. Furthermore, recent research has demonstrated that polymers can be obtained at conversions as high as 99%, providing an ideal tool for the synthesis of polymers for optoelectronic applications, where the monomers used can be costly. Polymers used in plastic electronics are often formed from π-conjugated pendant side chains attached to a linear all carbon backbone. Such polymers can be ideal candidates for polymerization by Cu(0)-RDRP, giving low-dispersity materials while reducing monomer waste. Unfortunately, complications arising from the coordination of monomers to a copper polymerization catalyst are eminent and cause complications in relation to ATRP procedures, most notably in the polymerization of poly(vinylimidazoles), which have numerous commercial applications.
Recently, University of British Columbia researchers in Canada led by Dr. Zachary Hudson developed a new method and optimized conditions for the Cu(0)-RDRP of several structurally diverse acrylic monomers based on p- and n-type organic semiconductors. Their main goal was to overcome the challenges encountered in the protocols for polymerizing similar N-donor materials for organic electronics using Cu(0)-RDRP. Their work is currently published in the research journal, Polymer Chemistry.
These methods allow for the synthesis of well-defined organic semiconductor polymers using simple copper wire as catalyst. “You can buy it from the hardware store,” says Hudson. “Copper wire is cheap and easy to handle, not to mention simple to remove at the end of the reaction.” After activating the wire by soaking in hydrochloric acid for 10 minutes to remove any impurities and the copper oxide coating, the reaction begins at room temperature as soon as the wire is added to the mixture. Solvents such as N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), or dimethylacetamide (DMAc) were found to provide the best balance of catalyst activity and solubility for the π-conjugated monomers used. Using these methods, it was possible to obtain organic semiconductors with low dispersities and molecular weights approaching 50,000 daltons.
The authors observed that the kinetic behavior of the substrates used was quite intrinsic, with the intricacy being attributed to the presence of N-donor atoms on all of the substrates that were studied, which portrayed the potential to interfere with the reversible deactivation radical polymerization equilibria involving Cu(0), Cu(I) and Cu(II) in the reaction. In addition, it was shown that controlled radical polymerization was still possible even when these monomers formed complexes with the cupric bromide present in the reaction. giving first-order kinetics after an initial induction period.
The study conducted by Dr. Zachary Hudson and his colleagues demonstrated that low-cost Cu(0)-RDRP methods can be useful in the synthesis of polymeric materials based on challenging substrates for organic semiconductors. All polymers examined showed good thermal stability with decomposition occurring in above 275 °C, making them ideal candidates for processing in organic devices in which similar n-type materials are commonly found. Altogether, the techniques advanced in their work provide a simple and inexpensive route to well-defined polymeric n-type organic semiconductors with potential applications in organic electronic devices such as OLEDs.
Christopher M. Tonge, Ethan R. Sauvé, Nathan R. Paisley, Jordan E. Heyes and Zachary M. Hudson. Polymerization of acrylates based on n-type organic semiconductors using Cu(0)-RDRP. Polymer Chemistry, 2018, volume 9, page 3359–3367 | 3359Go To Polymer Chemistry