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Mechanochemical unzipping of insulating polyladderene to semiconducting polyacetylene

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Science  04 Aug 2017:
Vol. 357, Issue 6350, pp. 475-479
DOI: 10.1126/science.aan2797

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Forcing polymers to be semiconductors

In mechanochemistry, the application of force to a polymer is used to pry open specific chemical bonds. Chen et al. leveraged this technique to produce semiconducting blocks of polyacetylene in an insulating precursor. Ring-opening metathesis polymerization tethered together a series of fused four-carbon rings, reminiscent of the unusual ladderane membrane lipids of anaerobic ammonium-oxidizing bacteria. Subsequently, sonication unzipped these strained rings into alternating C=C double bonds, thereby extending π-conjugation along the polymer backbone.

Science, this issue p. 475

Abstract

Biological systems sense and respond to mechanical stimuli in a complex manner. In an effort to develop synthetic materials that transduce mechanical force into multifold changes in their intrinsic properties, we report on a mechanochemically responsive nonconjugated polymer that converts to a conjugated polymer via an extensive rearrangement of the macromolecular structure in response to force. Our design is based on the facile mechanochemical unzipping of polyladderene, a polymer inspired by a lipid natural product structure and prepared via direct metathesis polymerization. The resultant polyacetylene block copolymers exhibit long conjugation length and uniform trans-configuration and self-assemble into semiconducting nanowires. Calculations support a tandem unzipping mechanism of the ladderene units.

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