Self-Strengthening of Cross-Linked Elastomers via the Use of Dynamic Covalent Macrocyclic Mechanophores

Abstract

The creation of polymeric materials that selfstrengthen in response to a mechanical force is an important objective in the field of polymer chemistry. Here, the mechanochemical strengthening of cross-linked elastomers using macrocyclic mechanophores that contain a dynamic covalent disulfide bond is reported. Cross-linked poly(hexyl methacrylate) (CPHMA) polymers with macrocyclic mechanophores inserted at the cross-linking points were synthesized via free radical polymerization. Tensile and swelling tests showed that the addition of the macrocyclic mechanophores to the CPHMA polymers successfully impart them with self-strengthening functionality following compression, without the need for any additives such as monomers and modifiers, or any other stimuli.

Force-modulated reductive elimination from platinum(ii) diaryl complexes

“…Over the last decade or so, coupled mechanical forces have been used to drive a range of targeted covalent responses in isolated polymers and in bulk polymeric materials (covalent polymer mechanochemistry). [1][2][3] Mechanochemical strategies continue to evolve, including their recent use in biasing and probing reaction pathways, 4,5 the release of small molecules and protons, [6][7][8] stress reporting, [9][10][11][12][13] stress strengthening, [14][15][16] degradable polymers, 17,18 and fundamental studies of polymer behaviour under load. 19 In organic reactions, mechanochemical coupling has been investigated in simple bond dissociation reactions [20][21][22][23][24] and in a wide variety of reaction classes with respect to regiochemistry, [25][26][27][28] orbital symmetry, 25,[29][30][31] stereochemistry, 32,33 supramolecular architecture, 34,35 dynamic effects, 36,37 and the alignment and/or loading of scissile bonds with applied tension.…”

Mechanical Performance and Visual Fracture Warning Function of Mechanochromic Stimuli-Recovery Polymer Networks

“…Mechanochromic P­(SMA–DMAA) networks gave us a clear signal for when they were threatening to break. Besides, the self-strengthening of the PHMA-based network, the scission of polystyrene chain, and force-induced cross-linking reactions in polyurethane elastomer were studied with different kinds of mechanochromic units, such as DFMA, diarylacetonitrile, and dynamic covalent disulfide bond. ,,,, It helped us gain more insight into the toughening mechanism of polymer materials through analyzing the stress distribution and tracking crack propagation. By integrating mechanochromic units into a polymer network, we can not only visualize the stress and access to fracture warning function, but also design mechanically robust materials with unique adaptive properties, including self-healing, topological rearrangement, and solid-state plasticity. − …”

Heterocyclic Mechanophores in Polymer Mechanochemistry

“…The weak bonds are defined as chemical bonds with a bond-dissociation energy (BDE) of less than 72 kcal mol -1 ; they are generally found in acyclic structures. These include covalent bonds such as diazo, 23,47 C-S, [48][49][50] C-C (in tetraarylsuccinonitrile), 25,28,[51][52][53][54][55][56] C-O, 50,57,58 S-S, [59][60][61][62] (Figure 2a), and coordinative bonds such as Ru-carbene, Ag-carbene, or Cucarbene bonds, 16,63 Fe-Cp (in ferrocene), [64][65][66] Pt-acetylide, 67 Fe-pyridine, 68 Cu-naphthalene, 69 Pd-phosphine, 70 and Pdcarbene (Figure 2b). 71 Covalent bonds in strained ring structures have lower BDEs than the analogous linear structures and can respond to mechanical forces.…”