Engineering Topochemical Polymerizations Using Block Copolymer Templates Liangliang Zhu, † Helen Tran, † Frederick L. Beyer, ‡ Scott D. Walck, ‡ Xin Li, § Hans Ågren, § Kato L. Killops,* ,∥ and Luis M. Campos* ,† † Department of Chemistry, Columbia University, New York, New York 10027, United States ‡ Army Research Laboratory, Aberdeen Proving Ground, Maryland 21005, United States § Division of Theoretical Chemistry and Biology, School of Biotechnology, KTH Royal Institute of Technology, SE-10691 Stockholm, Sweden ∥ Edgewood Chemical Biological Center, Aberdeen Proving Ground, Maryland 21010, United States * S Supporting Information ABSTRACT: With the aim to achieve rapid and efficient topochemical polymerizations in the solid state, via solution-based processing of thin films, we report the integration of a diphenyldiacetylene monomer and a poly(styrene-b-acrylic acid) block copolymer template for the generation of supramolecular architectural photopolymerizable materials. This strategy takes advantage of non-covalent interactions to template a topochemical photopolymerization that yields a polydiphenyldiacetylene (PDPDA) derivative. In thin films, it was found that hierarchical self-assembly of the diacetylene monomers by microphase segregation of the block copolymer template enhances the topochemical photopolymerization, which is complete within a 20 s exposure to UV light. Moreover, UV-active cross-linkable groups were incorporated within the block copolymer template to create micropatterns of PDPDA by photolithography, in the same step as the polymerization reaction. The materials design and processing may find potential uses in the microfabrication of sensors and other important areas that benefit from solution-based processing of flexible conjugated materials. ■ INTRODUCTION Chemical transformations in constrained media have enabled grand technological advancements and a deep fundamental understanding of reaction mechanisms. 1−4 While unimolecular processes have less stringent requirements to engineer reactivity in the solid state, 5−9 bimolecular and polymerization reactions can be challenging. 10−13 In the latter case, preorganization of the reactive components is crucial, where bond-making and bond-breaking must occur with minimal atom displacement. To align the building blocks, these topochemical transformations are generally carried out in highly ordered systems, such as molecular cages, 14 monolayers, 15,16 nanoporous materials, 17 and crystals. 18−20 The ability to template topochemical reactions in amorphous media (such as polymers), however, has received little attention due to the lack of control of intermolecular alignment of the reactive species. 3 Interestingly, block copolymers (BCPs) can lead to ordered phases where appropriate functionalization yields close packing arrange- ments. 21 Thus, we sought to exploit the use of side-chain supramolecular BCP templates to investigate chemical reactivity in constrained media. The seminal work by Wegner on the topochemical polymerization of diacetylene (DA) demonstrated that its molecular orientation was essential to react by 1,4-addition to yield polydiacetylene, a conjugated polymer. 22 With the growing interest for these materials to be exploited in excitonic photovoltaic devices (polydiacetylene undergoes singlet fission), 23 sensors, 24,25 bioelectronic materials, 26 and other optoelectronic devices, 27 the past decade has witnessed increased interest in controlling the polymerization of DAs. The key strategies have been based on grafting DA monomers on surfaces to form monolayers that are well-aligned 17 and introducing functional groups on the DA monomers to control their aggregation and crystallization, followed by thermal or photochemical polymerization. 18,28 The reactivity of such constructs is usually sluggish, where polymerization proceeds within minutes to hours by heating or UV light. 29,30 Recently, Shimizu and co-workers have shown that DA-containing macrocycles can crystallize with the appropriate arrangement for polymerization, though the reaction takes 3 h with heating. 31,32 Exploiting biomimetic supramolecular interactions, Tovar and co-workers found that the arrangement of diphenyldiacetylene (DPDA) monomers using oligopeptides can guide the supramolecular assembly, where photopolyme- rization occurs within 30 min to yield polydiphenyldiacetylene (PDPDA). 33 In all these cases, the polymerizations are system- specific and not amenable for thin-film processing. Solution- Received: July 18, 2014 Published: September 11, 2014 Article pubs.acs.org/JACS © 2014 American Chemical Society 13381 dx.doi.org/10.1021/ja507318u | J. Am. Chem. Soc. 2014, 136, 13381−13387