MECHANOCHEMISTRY

Mechanochemical unzipping ofinsulating polyladderene tosemiconducting polyacetyleneZhixing Chen,1 Jaron A. M. Mercer,1 Xiaolei Zhu,1,2,4 Joseph A. H. Romaniuk,1

Raphael Pfattner,3 Lynette Cegelski,1 Todd J. Martinez,1,2,4* Noah Z. Burns,1* Yan Xia1*

Biological systems sense and respond to mechanical stimuli in a complex manner. In aneffort to develop synthetic materials that transduce mechanical force into multifoldchanges in their intrinsic properties, we report on a mechanochemically responsivenonconjugated polymer that converts to a conjugated polymer via an extensiverearrangement of the macromolecular structure in response to force. Our design is basedon the facile mechanochemical unzipping of polyladderene, a polymer inspired by alipid natural product structure and prepared via direct metathesis polymerization. Theresultant polyacetylene block copolymers exhibit long conjugation length and uniformtrans-configuration and self-assemble into semiconducting nanowires. Calculationssupport a tandem unzipping mechanism of the ladderene units.

Mechanical force can induce chemical trans-formations that are inaccessible undertraditional thermal or photochemicalreaction manifolds (1–3). Force-basedsignaling manifests in macromolecules

that can transduce strong pulling or shearingforces along their backbone. In biological sys-tems, cellular transduction of mechanical stimulito electrical signals underlies tactile and auditorysensation, muscle contraction, and many otherimportant physiological processes (4). Emergentpolymer mechanochemistry has transformedchemists’ ability to explore force-induced reactivity:Various molecular motifs, termed mechano-phores, have been elaborately designed to undergoproductive chemical transformations in responseto mechanical stimuli, conferring force-responsiveproperties to polymers, such as coloration (5),luminescence (6, 7), self-strengthening (8), andself-demolishing (9), as well as release of smallmolecules (10, 11) and active catalysts (12). Mostexamples to date involve sparse incorporationof a reporter mechanophore into a mechano-chemically inert polymer; moving forward, acentral challenge is achieving (macro)moleculardesign to enable mechanochemical transforma-tions of an entire polymer chain, resulting in am-plified, synergistic changes to its molecular andmacroscopic properties. Herein, we report amacro-molecular scaffold that rearranges dramaticallyunder force, converting a series of strained s bondsto p bonds, thus transforming an insulating non-conjugated structure to a semiconducting struc-ture with continuous extended conjugation.

Conjugated polymers possess a range of distinctoptical, electronic, thermal, and mechanical prop-erties that are widely applied in sensing, imaging,energy harvesting, and flexible electronics (13).The ability to trigger these properties by mechan-ical stimulation would allow access to smart mate-rials with a suite of output responses and functionsupon mechanical input. Such a goal, however,presents two formidable challenges: (i) linking avast number of mechanophores repeatedly alongthe force path in a polymer chain and (ii) mechan-ically triggering the change of sp3 to sp2 hybridiza-tion state in a continuous stretch of backbonecarbons to establish extended conjugation.

Strained four-membered cyclobutane and cyclo-butene rings have been explored by Moore,Boulatov, and Craig as mechanophores to gener-ate a pair of olefins under force (1, 14–18). Wehypothesized that cyclobutenes (CBEs) mightbridge separate p motifs with an insulating yetmechanically labile s bond, allowing mechanicalactivation to establish continuous conjugation(Fig. 1A). Our initial efforts to synthesize variousCBEs with alkenyl or aryl substituents at the 3and 4 positions (1) failed, presumably due tofacile thermal electrocyclic ring-opening at roomtemperature (Fig. 1B) (19, 20). Seeking an al-ternative strategy, we postulated that fusionof one or more mechanically active cyclobutanerings between the CBE and the destabilizing plinkages could enhance thermal stability (Fig. 1C).Our inspiration came from the intriguing struc-ture of the naturally occurring ladderane lipids(as in fatty acid 5, Fig. 1D), which make up a largefraction of the membrane lipids produced byanaerobic ammonium oxidizing (anammox)bacteria (21). We envisioned that multiple fusedcyclobutanes in [n]-ladderanes (where n refersto the number of fused four-membered rings)could undergo tandem [2+2] cycloreversions viamechanochemical unzipping to generate oligoenes(Fig. 1C). Some of us recently developed a con-cise total synthesis of [5]-ladderane lipids (22).Therefore, we designed our ladderene mechano-phore monomer based on [5]-ladderane (Fig. 1E),although ladderenes of any length (any n) could beleveraged as mechanophores to generate oligoenesin principle. The next step in the design requiredconnecting repeated ladderene structures efficientlyinto a polymer: Direct polymerization of mechano-phores seemed the simplest and most effectiveway to synthesize the mechanochemically activepolymers. We anticipated that simple ring-opening

RESEARCH

Chen et al., Science 357, 475–479 (2017) 4 August 2017 1 of 4

1Department of Chemistry, Stanford University, Stanford, CA94305, USA. 2The PULSE Institute, Stanford University,Stanford, CA 94305, USA. 3Department of ChemicalEngineering, Stanford University, Stanford, CA 94305, USA.4SLAC National Accelerator Laboratory, Menlo Park, CA94025, USA.*Corresponding author. Email: toddmtz@stanford.edu (T.J.M.);nburns@stanford.edu (N.Z.B.); yanx@stanford.edu (Y.X.)

Fig. 1. Design of mechanochemically generated conjugated polymer. (A) Insulating CBE mechano-phores connected with p systems, designed to rearrange to continuously extended conjugation underforce. (B) Thermally unstable CBEs with sp2 carbon substituents at the 3 and 4 positions. (C) Ladderene-based mechanophore, which would undergo tandem mechano-cycloreversions to give conjugatedoligoene. (D) Natural [5]-ladderane fatty acid (5) from anammox bacteria. (E) Design of mechanicallyactive polyladderene via ROMP of ladderene.

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metathesis polymerization (ROMP) (23) would bean ideal method to polymerize ladderene, drivenby the release of CBE strain, and also conve-niently generate the requisite polymer backbonep-bond connection between mechanophores (Fig.1E). Polyladderenes of this type comprise exclu-sively methine carbons and would be expectedto unzip to polyacetylene (PA) (24) upon success-ful mechanochemical activation.We designed chloroladderene 10 (Fig. 2A)

as the ROMP monomer for the synthesis ofpolyladderene. Chloroladderene 10 is a latentladderdiene: One CBE undergoes ROMP to givelinear poly(chloroladderane) 11; subsequent-ly, the second CBE is unmasked at the end ofeach ladder by elimination of HCl to give poly-ladderene 7. We prepared 10 from previouslysynthesized chloroladderane 8 (22) via a secondchlorination under Groves’ Mn-porphyrin con-ditions (25), followed by elimination of one ofthe chlorides with KOt-Bu. Monomer 10 readilypolymerized to nearly full conversion within 1 hourat room temperature in chloroform upon addi-tion of 0.1 to 0.5 mole % (mol %) of fast-initiatingGrubbs III catalyst. Gel permeation chromatogra-phy (GPC) analysis of the resulting poly(chloro-ladderane) 11 revealed a narrow molecular weight(MW) distribution with MW proportional to themonomer-to-catalyst ratio, which was varied from200 to 1000 (Fig. 2B). These features indicatedcontrolled ROMP to be an efficient strategy toproduce polymers with hundreds of linkedmechano-phores. Treatment of the polymer 11 with 1 MKOt-Bu in tetrahydrofuran (THF) at 16°C yieldedpolyladderene 7with complete elimination of HCland generation of a terminal CBE on all ladderside chains (Fig. 2C). Polymers 7 showed slowerelution in GPC and a decrease in MW comparedwith their corresponding precursors 11 (7a, 7b,and 7c: Mn = 93, 63, and 34 kDa, respectively).For the very-high-MW polymer (7a), broadeningof the MW distribution was observed afterelimination; however, high-MW polyladdereneswere still obtained.We then studied the mechanochemical activa-

tion of polyladderene 7a in THF solution using

controlled ultrasonication, a convenient andstandard technique to apply mechanical forcein an acoustic flow and thereby study polymermechanochemistry (Fig. 3A). After only 20 s ofsonication, the initially colorless polymer solu-tion turned blue and then continued to darken.After 120 min of sonication, the reaction mixturehad turned dark blue/purple, with concomitantformation of black precipitate on the side of theglass vessel (Fig. 3B). Solution aliquots were drawnwith a syringe at different time points duringsonication and analyzed by ultraviolet-visible(UV-vis) spectroscopy (Fig. 3C). A broad absorp-tion peak with a maximum over 600 nm and anonset at 850 nm were clearly and consistentlyobserved throughout the course of sonication.These observed wavelengths are among the highestreported for solution-synthesized PAs (26–29),suggesting the formation of PA blocks with longconjugation lengths. The absorption peak con-tinuously grew in intensity during the sonica-tion process, indicating continuous formation ofPA. After 120 min of sonication, the absorptionmaximum slightly shifted hypsochromically to605 nm with a concomitant decrease in solubilityand formation of particulates due to the relativelyhigh content of insoluble PA. Long-wavelengthabsorption was observed even at the beginningof sonication, when the absorbance was stilllow (fig. S1). This observation suggests that, eventhough only a small fraction of the polymer solu-tion was processed at each pulse of sonication, longstrands of PA, rather than multiple segments ofoligoenes, were rapidly formed within that fractionof sample. To prove the mechanochemical natureof the polyladderene transformation, we subjectedpolyladderenes of different MWs to identicalsonication conditions. The kinetics of the mechano-chemical formation of PA strongly dependedon the MW of precursor polymer: Polyladdereneswith lower MWs formed PA more slowly butwith similar optical absorption profiles (fig. S2).Because thermal activation is not affected bythe polymer MW, these MW-dependent kineticsare commonly regarded as strong evidence formechanochemistry.

We applied several spectroscopic and micro-scopic methods to characterize the structure ofmechanochemically generated PA copolymer 12.Cross-polarization magic-angle spinning 13C solid-state nuclear magnetic resonance (NMR) spectros-copy was used to analyze the isolated activatedpolymer. A carbon resonance at 136 parts permillion corresponding to trans-PA was clearlyobserved (30), along with the signals associatedwith the residual polyladderene (Fig. 3D). Basedon the integrations of sp2 and sp3 carbon signals,the conversion of polyladderene 7a to PA wasdetermined to be ~37% after 120 min of sonication(fig. S3).Resonant Raman spectra (785-nm excitation)

of samples after 20 s and 20 min of sonicationexhibited vibrational peaks at 1463 and 1073 cm−1,matching the C=C and C−C stretching peaks fortrans-PA, respectively (Fig. 3E) (31). Both theRaman frequency at 1463 cm−1 and visible absorp-tion peak at 636 nm suggested the formation ofvery long trans-PA with > 100 conjugated C=Cbonds, based on the reported correlations (32).Infrared (IR) spectra of the resulting polymer 12exhibited an intense peak at 1012 cm−1, corre-sponding to the reported C−H bending of trans-PA, as well as peaks at 2924 and 2851 cm−1 for theC−H stretches of cyclobutane in the remaining un-activated ladderene (fig. S5). No signals corre-sponding to cis configuration of PA were observedwithin the detection limit of IR or 13C NMR exper-iments (figs. S3 and S5). Because each laddereneside chain bears a cis-olefin at the terminus, theabsence of cis-olefin signals suggests simulta-neous mechanochemical cis-to-trans isomerizationduring the PA generation. These spectroscopicdata collectively confirmed the mechanochem-ical transformation of polyladderene to trans-PAwith remarkably uniform configuration and longconjugation length.The force exerted onto a polymer chain via

sonication is known to peak near the middle ofthe chain (33). Thus, we expect mechanochemicalunzipping to occur from the middle of the chainwhere the force is above the activation threshold,resulting in the formation of ABA-type triblock

Chen et al., Science 357, 475–479 (2017) 4 August 2017 2 of 4

Fig. 2. Synthesis of polyladderene.(A) Synthetic route to polyladderene7. (a) Mn(III) meso-tetra(2,4,6-trimethylphenyl)porphine chloride(5 mol %), NaOCl (7.2 equiv.), tetra-n-butylammonium chloride (12 mol %),CH2Cl2/H2O, 23°C, 4 hours, 37%,31% recovered starting material(rsm). (b) KOt-Bu (1 equiv.), THF,35°C, 3 hours, 49%, 38% rsm.(c) Grubbs III catalyst (0.1, 0.25, or0.5 mol %), CHCl3, 25°C, 6 hours,quantitative conversion. (d) KOt-Bu(50 equiv.), THF, 16°C, 40 hours,quantitative conversion. (B) GPCtraces of polymers 11, a to c, and 7,a to c. (C) 1H NMR spectra ofpolymers 11 and 7.

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Fig. 3. Characterization ofthe mechanochemicallygenerated PA copolymerfrom polyladderene.(A) Reaction scheme formechanochemical conver-sion of polyladderene 7 toPA-containing blockcopolymer 12. (B) Photo-graphs of reaction vessel atdifferent sonication times.(C) UV-vis absorptionspectra of sonicated 7asolution at different sonica-tion times. (D) Overlaidsolid-state 13C NMR spectraof polymers 7a and 12a after120 min of sonication.(E) Resonance Ramanspectra of the sonicationproducts (785-nm laser exci-tation). (F) TEM images ofthe nanostructures formedduring sonication (scale bar,200 nm) and proposedsonication-induced self-assembly of the resultantblock copolymer.

Fig. 4. Theoreticalsimulation of theunzipping process ofa ladderene unit.(A) Proposed reactionpathway for mecha-nochemical unzippingof a single ladderene.(B) Force-modifiedpotential energy sur-face showing consec-utive ring openings ofthe cyclobutane unitsin the ladderene togive an oligoene.(C) Force-extensioncurve simulated usingmolecular dynamics.

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copolymers with insoluble PA in the middle andsoluble unactivated polyladderene at the ends(Fig. 3A). PA-containing block copolymers aredifficult to synthesize (26–28), especially in all-trans configuration. The trans-PA copolymerswere expected to self-assemble into unique nano-structures driven by the aggregation of the longPA block and stabilization of the unactivatedpolyladderene block. Indeed, dynamic light scat-tering (DLS) of the sonicated solutions showedthe formation of micelles with a hydrodynamicradius growing from 115 to 500 nm, as sonicationtime increased from 20 s to 20 min (fig. S6).Transmission electron microscopy (TEM) of thesesamples revealed evolution of nanostructures(Fig. 3F) in this time frame from spherical micellesto elongated and interconnected wormlike struc-tures. After 2 hours of sonication, meshes of in-terconnected nanowires were clearly observed.These nanowires were presumably composed of anaggregated PA core encapsulated by a solubilizingpolyladderene corona. To measure the electricalconductivity of these encapsulated PA nanowires,we drop-cast the solution of activated sample ontoa microelectrode array to form a film by simplesolvent evaporation without doping or anneal-ing or alignment (fig. S7). We measured a con-ductivity of 2.6 × 10−7 S/cm, which is about twoorders of magnitude lower than the reportedvalue for Shirakawa’s surface-grown alignedtrans-PA film sample (24). This relatively lowconductivity is still a compelling initial result,considering the encapsulation by an insulatingcorona and the meshed, rather than bulk, nano-wire structures. The measured conductivity furthersupported the formation of an interconnectednetwork of semiconducting PA domains.To gain more insight into the facile mechano-

chemistry of polyladderene, we first computedthe force-modified potential energy surface(FMPES) for the unzipping of a single laddereneunder different pulling forces (Fig. 4, A and B).Calculations were performed on model ladderene13; attachment points (atoms where the forceis exerted) were chosen as the carbon atoms far-thest from the ladderane core. For a series of ex-ternal forces ranging from 0 to 3 nN, minimumenergy pathways were optimized using the nudgedelastic band (NEB) method (34), which yields re-action coordinates and energy profiles. Electronicstructure calculations were performedwith graphicsprocessing unit (GPU)–accelerated complete activespace self-consistent field (CASSCF) theory (35)with 6-31 g* basis. The CASSCF method is advan-tageous in this case because it can accurately de-scribe a multireference character in the electronicwave function, which is critical for potential rad-ical intermediates. We found a single barrier foreach of the two sequential cyclobutane unzip-ping events, which involve simultaneous breakingof two s bonds and formation of two p bonds(these are the four electrons and orbitals in the

active space). The structure with two openedrungs (15) is a metastable intermediate, whereasthe structures with 1 or 3 opened rungs (14 and16, respectively) are transient transition states.Inspection of the electronic wave function con-firmed that transition-state structures are di-radicals with a strong multireference character(table S1). According to Fig. 4B, two consecutivelarge barriers have to be surmounted for theunzipping event to take place in the absence ofpulling force. Application of force lowers thesebarriers; the second barrier remains slightly lowerthan the first at all force levels (fig. S20), and bothbecome negligible at 3.0 nN force, at which pointthe unzipping process becomes spontaneous.We further calculated the force-extension curve

for one ladderene unit on the FMPES at UB3LYP/6-31 g* level of theory (Fig. 4C). Comparisonwith CASSCF was used to validate the choiceof exchange-correlation functional and to ensuredensity functional theory convergence to thediradical solution (fig. S21). Constant temper-ature ab initio steered molecular dynamics (36)at 279 K was performed for 10 ps at each of avariety of external forces ranging from 0 to 4.5 nN.For each external force, the contour lengthcorresponding to one monomer was recordedat the end of the simulation by taking the averageof distances over the last 0.5 ps of the simulation.Equilibrium analysis at 0 K was also performed tocorroborate the molecular dynamics analysis(fig. S23). The force-extension curve has a singleplateau at 3.1 nN force with the monomerextending by 10 Å or twice the contour lengthat unzipping of the entire ladderene (Fig. 4C),and the intermediate 15 was not observed. Thisall-or-none unzipping behavior is consistent withthe reaction barrier analysis and suggests thatladderene is a privileged design motif for gen-erating oligoenes with continuous extendedconjugation.We envision the emergence of additional force-

responsive polymers that undergo mechanicallytriggered macromolecular structural reconfig-uration and drastically change their intrinsicproperties, thereby converting mechanical stimuliinto a diverse array of functions.

REFERENCES AND NOTES

1. C. R. Hickenboth et al., Nature 446, 423–427 (2007).2. J. M. Lenhardt et al., Science 329, 1057–1060 (2010).3. J. Li, C. Nagamani, J. S. Moore, Acc. Chem. Res. 48, 2181–2190

(2015).4. M. Chalfie, Nat. Rev. Mol. Cell Biol. 10, 44–52 (2009).5. D. A. Davis et al., Nature 459, 68–72 (2009).6. Y. Chen et al., Nat. Chem. 4, 559–562 (2012).7. E. Ducrot, Y. Chen, M. Bulters, R. P. Sijbesma, C. Creton,

Science 344, 186–189 (2014).8. A. L. Ramirez et al., Nat. Chem. 5, 757–761 (2013).9. C. E. Diesendruck et al., Nat. Chem. 6, 623–628 (2014).10. M. B. Larsen, A. J. Boydston, J. Am. Chem. Soc. 135,

8189–8192 (2013).11. C. E. Diesendruck et al., J. Am. Chem. Soc. 134, 12446–12449

(2012).

12. A. Piermattei, S. Karthikeyan, R. P. Sijbesma, Nat. Chem. 1,133–137 (2009).

13. T. A. Skotheim, J. Reynolds, Conjugated Polymers: Theory,Synthesis, Properties, and Characterization (CRC Press, 2006).

14. Q. Z. Yang et al., Nat. Nanotechnol. 4, 302–306 (2009).15. M. J. Kryger et al., J. Am. Chem. Soc. 132, 4558–4559 (2010).16. M. J. Kryger, A. M. Munaretto, J. S. Moore, J. Am. Chem. Soc.

133, 18992–18998 (2011).17. Z. S. Kean, A. L. Black Ramirez, Y. Yan, S. L. Craig, J. Am.

Chem. Soc. 134, 12939–12942 (2012).18. Z. S. Kean, Z. Niu, G. B. Hewage, A. L. Rheingold, S. L. Craig,

J. Am. Chem. Soc. 135, 13598–13604 (2013).19. J. I. Brauman, W. C. Archie Jr., Tetrahedron 27, 1275–1280 (1971).20. K. Rudolf, D. C. Spellmeyer, K. N. Houk, J. Org. Chem. 52,

3708–3710 (1987).21. J. S. Sinninghe Damsté et al., Nature 419, 708–712 (2002).22. J. A. M. Mercer et al., J. Am. Chem. Soc. 138, 15845–15848

(2016).23. R. H. Grubbs, E. Khosravi, Handbook of Metathesis, Volume 3:

Polymer Synthesis, 2nd Ed. (Wiley-VCH, 2015).24. H. Shirakawa, E. J. Louis, A. G. MacDiarmid, C. K. Chiang,

A. J. Heeger, J. Chem. Soc. Chem. Commun. 16, 578–580(1977).

25. W. Liu, J. T. Groves, J. Am. Chem. Soc. 132, 12847–12849(2010).

26. G. L. Baker, F. S. Bates, Macromolecules 17, 2619–2626(1984).

27. O. A. Scherman, I. M. Rutenberg, R. H. Grubbs, J. Am. Chem.Soc. 125, 8515–8522 (2003).

28. K.-Y. Yoon et al., J. Am. Chem. Soc. 134, 14291–14294 (2012).29. C. B. Gorman, E. J. Ginsburg, R. H. Grubbs, J. Am. Chem. Soc.

115, 1397–1409 (1993).30. H. W. Gibson, S. Kaplan, R. A. Mosher, W. M. Prest,

R. J. Weagley, J. Am. Chem. Soc. 108, 6843–6851 (1986).31. I. Harada, M. Tasumi, H. Shirakawa, S. Ikeda, Chem. Lett. 7,

1411–1414 (1978).32. F. B. Schügerl, H. Kuzmany, J. Chem. Phys. 74, 953–958 (1981).33. T. Q. Nguyen, H.-H. Kausch, in Macromolecules: Synthesis,

Order and Advanced Properties (Springer, Berlin, Heidelberg,1992), pp. 73–182.

34. M. U. Bohner, J. Meisner, J. Kästner, J. Chem. Theory Comput.9, 3498–3504 (2013).

35. E. G. Hohenstein, N. Luehr, I. S. Ufimtsev, T. J. Martínez,J. Chem. Phys. 142, 224103 (2015).

36. M. T. Ong, J. Leiding, H. Tao, A. M. Virshup, T. J. Martínez,J. Am. Chem. Soc. 131, 6377–6379 (2009).

ACKNOWLEDGMENTS

This work was supported by the U.S. Army Research Office undergrant number W911NF-15-1-0525 and Stanford University. J.A.M.M.thanks the National Science Foundation for a graduate fellowship.R.P. acknowledges support from Marie Curie Cofund, Beatriu dePinós fellowship (AGAUR 2014 BP-A 00094). T.J.M. acknowledgessupport from Office of Naval Research grant N00014-12-1-0828and the Global Climate and Energy Project. This work used theXStream computational resource supported by the NationalScience Foundation Major Research Instrumentation program(ACI-1429830). L.C. acknowledges support from the NationalScience Foundation CAREER Award 1453247. We thankJ. I. Brauman for helpful discussion, Z. Bao for conductivitymeasurement, A. F. Marshall at Stanford Nano Shared Facilities forhelping with TEM imaging, and Materia Inc. for a gift of Grubbscatalyst. All data are available in the supplementary materials.The authors declare no competing financial interest.

SUPPLEMENTARY MATERIALS

www.sciencemag.org/content/357/6350/475/suppl/DC1Materials and MethodsSupplementary TextFigs. S1 to S23Tables S1 to S6Movies S1 and S2References (37–46)

23 March 2017; accepted 15 June 201710.1126/science.aan2797

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Mechanochemical unzipping of insulating polyladderene to semiconducting polyacetylene

Noah Z. Burns and Yan XiaZhixing Chen, Jaron A. M. Mercer, Xiaolei Zhu, Joseph A. H. Romaniuk, Raphael Pfattner, Lynette Cegelski, Todd J. Martinez,

DOI: 10.1126/science.aan2797 (6350), 475-479.357Science 

, this issue p. 475Science-conjugation along the polymer backbone.πalternating C=C double bonds, thereby extending

membrane lipids of anaerobic ammonium-oxidizing bacteria. Subsequently, sonication unzipped these strained rings intometathesis polymerization tethered together a series of fused four-carbon rings, reminiscent of the unusual ladderane

leveraged this technique to produce semiconducting blocks of polyacetylene in an insulating precursor. Ring-openingal.etIn mechanochemistry, the application of force to a polymer is used to pry open specific chemical bonds. Chen

Forcing polymers to be semiconductors

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