Abstract
Two series of well-defined brush polymers bearing a triazole moiety on each bristle were prepared from the click chemistry reactions of a poly(glycidyl azide) (PG) and a poly(4-azidomethylstyrene) (PS) with alkyne derivatives. The thin-film morphologies and properties, especially electrical memory performances, of these triazole-containing brush polymers were investigated in detail. The brush polymers with a triazole ring substituted with an alkyl or alkylenylphenyl group in the bristle exhibited only dielectric characteristics. By contrast, the other brush polymers bearing a triazole ring substituted with phenyl or its derivatives with a longer π-conjugation length in the bristle demonstrated excellent unipolar permanent memory behaviors with low power consumption, high ON/OFF current ratios and high stability and reliability under ambient air conditions. Furthermore, their memory type could be tuned to p- or n-type by the incorporation of an electron-donating or -accepting group into the phenyl unit linked to the triazole moiety. Overall, this study presents the first demonstration of the azide–alkyne click chemistry synthesis of triazole moieties with substituent(s) that exhibit a resonance effect; this approach is a very powerful synthetic route to develop electrical memory polymers suitable for the low-cost mass production of high-performance, polarity-free programmable memory devices. A programmable memory cell based on nanoscale polymer thin films is easier to produce and consumes less power than typical devices. Electrical memory polymers contain networks of conjugated molecules that can switch to high- or low-resistance off and on states using moderate voltages. To improve the processing and performance of these materials, Moonhor Ree from POSTECH in South Korea and co-workers turned to ‘click’ chemistry — an approach that connects small molecules together quickly and with minimal by-products. The team used conventional casting methods with organic solvents to tether polymer 'bristles' decorated with nitrogen-containing triazole rings to electrode surfaces. Experiments showed that a unique resonance effect between the triazole rings gave high on/off current ratios and low switching-on voltages, while the click synthesis produced a smooth, nanoscale interface with desirable stability under ambient conditions. This study demonstrated that the formation of triazole moieties accompanying with a linker or substituent group(s) having a resonance effect (which can provide a charge stabilization power) by using azide–alkyne click chemistry is a very powerful synthetic route to develop electrical memory polymers with high performances. The memory mode can be further tuned by changing the linker or substituent group(s) in the triazole moiety.
Highlights
IntroductionSince click chemistry was introduced in 2001,1 it has become one of the most powerful synthetic tools to develop functional polymers.[2]Through click chemistry reactions, desired functional moieties can be incorporated into polymers as side groups, pr oducing functionalized polymers.[2,3,4,5,6] In particular, Cu(I)-catalyzed azide–alkyne cycloaddition has been well established as a representative click chemistry reaction capable of selectively combining two components via covalent bonds in excellent yields.[1,2,3,4,5,6,7] This click reaction, has some drawbacks, such as the requirement of a metal-based catalyst for achieving a high reaction conversion and controlling regioselectivity, the explosive nature of some azide substances and the negative effects of the formed triazole ring on solubility and other properties such as electronic and optoelectronic properties.[8]
This study presents the first demonstration of the azide–alkyne click chemistry synthesis of triazole moieties with substituent(s) that exhibit a resonance effect; this approach is a very powerful synthetic route to develop electrical memory polymers suitable for the low-cost mass production of high-performance, polarity-free programmable memory devices
Two series of brush polymers bearing a single triazole moiety in the bristle per repeat unit were successfully synthesized via the azide–alkyne click chemistry reaction, as described in the experimental section: poly(glycidyl azide) (PG)-Triazole-C10, PG-Triazole-C2P, PG-Triazole-P, PS-Triazole-PEP, PS-Triazole-PTCNE, and PS-Triazole-PTCNQ
Summary
Since click chemistry was introduced in 2001,1 it has become one of the most powerful synthetic tools to develop functional polymers.[2]Through click chemistry reactions, desired functional moieties can be incorporated into polymers as side groups, pr oducing functionalized polymers.[2,3,4,5,6] In particular, Cu(I)-catalyzed azide–alkyne cycloaddition has been well established as a representative click chemistry reaction capable of selectively combining two components via covalent bonds in excellent yields.[1,2,3,4,5,6,7] This click reaction, has some drawbacks, such as the requirement of a metal-based catalyst for achieving a high reaction conversion and controlling regioselectivity, the explosive nature of some azide substances and the negative effects of the formed triazole ring on solubility and other properties such as electronic and optoelectronic properties.[8]. Extensive effort has been devoted to overcome such drawbacks, resulting in the development of metal-free azide–alkyne click chemistry as well as azide-free click chemistry.[9,10,11,12,13,14,15] the drawbacks arising from triazole ring formation have not yet been solved
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