All Publications


  • Mechanochemical generation of acid-degradable poly(enol ether)s. Chemical science Yang, J., Xia, Y. 2021; 12 (12): 4389-4394

    Abstract

    In an effort to develop polymers that can undergo extensive backbone degradation in response to mechanical stress, we report a polymer system that is hydrolytically stable but unmasks easily hydrolysable enol ether backbone linkages when force is applied. These polymers were synthesized by ring-opening metathesis polymerization (ROMP) of a novel mechanophore monomer consisting of cyclic ether fused bicyclohexene. Hydrogenation of the resulting polymers led to significantly enhanced thermal stability (Td > 400 °C) and excellent resistance toward acidic or basic conditions. Solution ultrasonication of the polymers resulted in up to 65% activation of the mechanophore units and conversion to backbone enol ether linkages, which then allowed facile degradation of the polymers to generate small molecule or oligomeric species under mildly acidic conditions. We also achieved solid-state mechano-activation and polymer degradation via grinding the solid polymer. Force-induced hydrolytic polymer degradability can enable materials that are stable under force-free conditions but readily degrade under stress. Facile degradation of mechanically activated polymechanophores also facilitates the analysis of mechanochemical products.

    View details for DOI 10.1039/d1sc00001b

    View details for PubMedID 34163702

    View details for PubMedCentralID PMC8179558

  • Bicyclohexene-peri-naphthalenes: Scalable Synthesis, Diverse Functionalization, Efficient Polymerization, and Facile Mechanoactivation of Their Polymers. Journal of the American Chemical Society Yang, J., Horst, M., Werby, S. H., Cegelski, L., Burns, N. Z., Xia, Y. 2020; 142 (34): 14619–26

    Abstract

    Pursuing polymers that can transform from a nonconjugated to a conjugated state under mechanical stress to significantly change their properties, we developed a new generation of ladder-type mechanophore monomers, bicyclo[2.2.0]hex-5-ene-peri-naphthalene (BCH-Naph), that can be directly and efficiently polymerized by ring-opening metathesis polymerization (ROMP). BCH-Naphs can be synthesized in multigram quantities and functionalized with a wide range of electron-rich and electron-poor substituents, allowing tuning of the optoelectronic and physical properties of mechanically generated conjugated polymers. Efficient ROMP of BCH-Naphs yielded ultrahigh molecular weight polymechanophores with controlled MWs and low dispersity. The resulting poly(BCH-Naph)s can be mechanically activated into conjugated polymers using ultrasonication, grinding, and even simple stirring of the dilute solutions, leading to changes in absorption and fluorescence. Poly(BCH-Naph)s represent an attractive polymechanophore system to explore multifaceted mechanical response in solution and solid states, owing to the synthetic scalability, functional diversity, efficient polymerization, and facile mechanoactivation.

    View details for DOI 10.1021/jacs.0c06454

    View details for PubMedID 32786795

  • The cascade unzipping of ladderane reveals dynamic effects in mechanochemistry. Nature chemistry Chen, Z., Zhu, X., Yang, J., Mercer, J. A., Burns, N. Z., Martinez, T. J., Xia, Y. 2020

    Abstract

    Force can induce remarkable non-destructive transformations along a polymer, but we have a limited understanding of the energy transduction and product distribution in tandem mechanochemical reactions. Ladderanes consist of multiple fused cyclobutane rings and have recently been used as monomeric motifs to develop polymers that drastically change their properties in response to force. Here we show that [4]-ladderane always exhibits 'all-or-none' cascade mechanoactivations and the same stereochemical distribution of the generated dienes under various conditions and within different polymer backbones. Transition state theory fails to capture the reaction kinetics and explain the observed stereochemical distributions. Ab initio steered molecular dynamics reveals unique non-equilibrium dynamic effects: energy transduction from the first cycloreversion substantially accelerates the second cycloreversion, and bifurcation on the force-modified potential energy surface leads to the product distributions. Our findings illustrate the rich chemistry in closely coupled multi-mechanophores and an exciting potential for effective energy transduction in tandem mechanochemical reactions.

    View details for DOI 10.1038/s41557-019-0396-5

    View details for PubMedID 31907403

  • Benzoladderene Mechanophores: Synthesis, Polymerization, and Mechanochemical Transformation. Journal of the American Chemical Society Yang, J., Horst, M., Romaniuk, J. A., Jin, Z., Cegelski, L., Xia, Y. 2019

    Abstract

    We have previously reported a polymechanophore system, polyladderene, which underwent dramatic bond rearrangement in response to mechanical force to yield semiconducting polyacetylene. Herein, we report the scalable synthesis of benzoladderenes as new mechanophore monomers. Ring-opening metathesis polymerization of benzoladderenes yielded homopolymers and block copolymers with controlled molecular weights and low dispersity. The resulting nonconjugated poly(benzoladderene) was mechanochemically transformed into conjugated poly( o-phenylene-hexatrienylene) by sonication, with degrees of transformation up to 40-45%. These benzoladderenes and their resulting polymers are easier to synthesize than the polyladderene system and allow mechanochemical generation of conjugated polymersbeyond polyacetylene.

    View details for PubMedID 30969109

  • Synthesis and Mechanochemical Activation of Ladderene-Norbornene Block Copolymers. Journal of the American Chemical Society Su, J. K., Feist, J. D., Yang, J., Mercer, J. A., Romaniuk, J. A., Chen, Z., Cegelski, L., Burns, N. Z., Xia, Y. 2018; 140 (39): 12388–91

    Abstract

    We have recently reported a polymechanophore system, polyladderene (PLDE), which dramatically transforms into polyacetylene (PA) upon mechanical stimulation. Herein, we optimized conditions to synthesize unprecedented block copolymers (BCPs) containing a force-responsive block by sequential ring-opening metathesis polymerization of different norbornenes and bromoladderene. Successful extension from PLDE to other blocks required careful timing and low temperatures to preserve the reactivity of the PLDE-appended catalyst. The PLDE-containing BCPs were sonochemically activated into visually soluble PA with a maximum absorption lambda ≥ 600 nm and unique absorption patterns corresponding to noncontinuous activation of ladderene units. Access to polymechanophore BCPs paves the way for new stress-responsive materials with solution and solid state self-assembly behaviors and incorporation of polymechanophores into other materials.

    View details for PubMedID 30229652

  • Synthesis and Mechanochemical Activation of Ladderene-Norbornene Block Copolymers JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Su, J. K., Feist, J. D., Yang, J., Mercer, J. M., Romaniuk, J. H., Chen, Z., Cegelski, L., Burns, N. Z., Xia, y. 2018; 140 (39): 12388-12391
  • Propeller-Shaped Acceptors for High-Performance Non-Fullerene Solar Cells: Importance of the Rigidity of Molecular Geometry CHEMISTRY OF MATERIALS Wu, Q., Zhao, D., Yang, J., Sharapov, V., Cai, Z., Li, L., Zhang, N., Neshchadin, A., Chen, W., Yu, L. 2017; 29 (3): 1127-1133
  • C-H Bond Functionalization of Benzoxazoles with Chromium(0) Fischer Carbene Complexes ORGANOMETALLICS Hu, F., Yang, J., Xia, Y., Ma, C., Xia, H., Zhang, Y., Wang, J. 2016; 35 (10): 1409-1414
  • Catalyst-free cross-coupling of N-tosylhydrazones with chromium(0) Fischer carbene complexes: a new approach to diarylethanone ORGANIC CHEMISTRY FRONTIERS Hu, F., Yang, J., Xia, Y., Ma, C., Xia, H., Zhang, Y., Wang, J. 2015; 2 (11): 1450-1456

    View details for DOI 10.1039/c5qo00241a

    View details for Web of Science ID 000364450200003