Synthesis and thin-film self-assembly of radical-containing diblock copolymers
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olymers/Soft Matter Research Letter
Synthesis and thin-film self-assembly of radical-containing diblock copolymers Lizbeth Rostro, Aditya G. Baradwaj, Alexander R. Muller, Jennifer S. Laster, and Bryan W. Boudouris, School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, West Lafayette, Indiana 47907, USA Address all correspondence Bryan W. Boudouris at [email protected] (Received 2 February 2015; accepted 24 April 2015)
Abstract Electronically active block polymers based on π-conjugated macromolecules have been investigated for applications where nanostructured electrodes are of prime import; however, controlling the nanoscale order of these materials has proven challenging. Here, we demonstrate that diblock copolymers that utilize a non-conjugated radical polymer moiety as the electronically active block assemble into ordered thin-film nanostructures. Specifically, the diblock copolymer polydimethylsiloxane-b-poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PDMS–PTMA) was synthesized via atom transfer radical polymerization to generate polymers with readily controlled molecular properties. Importantly, solvent annealing of the PDMS–PTMA thin films led to well-defined nanostructures with domain spacings of the order of ∼30–40 nm.
Introduction Block polymers that demonstrate tailored morphologies have been utilized for a range of applications extending from nanolithography[1–3] to membrane separations[4,5] through organic electronic devices[6–8] due to the regular ordering of nanoscale features. Importantly, the thin-film self-assembly behavior of block polymers containing both relatively flexible (coil-like) segments and rigid (rod-like) segments has been investigated heavily from theoretical, computational, and experimental views.[9–12] Recently, Suga et al.[13] demonstrated, for the first time, the formation of thin-film structures in radical containing diblock systems; however, these results did not show well-ordered behavior or long-range order and many questions remain regarding the self-assembly in this class of macromolecules. This is despite the fact that polymers bearing stable radical groups on the side chains of their flexible macromolecular backbones (i.e., radical polymers) are emerging as promising materials in many organic electronic applications (e.g., flexible batteries and polymer-based photovoltaic devices).[14–17] Here, we synthesize well-defined diblock copolymers containing a radical polymer moiety and elucidate the nanostructure of radical polymer-based diblock copolymer thin films. Furthermore, these nanostructured thin films demonstrate the viability of using block polymer motifs as a means by which to create electronically active nanostructured radical polymers for myriad organic electronic applications (e.g., nanostructured electrodes in flexible solid-state batteries).[18,19] The implementation of semiconducting and conducting moieties in block polymer materials is an increasingly studied field because controlling the nanostructure of many organic electronic devices is of pr
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