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. 2022 Jan 18;13(1):356.
doi: 10.1038/s41467-022-28017-0.

Mechanically robust supramolecular polymer co-assemblies

Julien Sautaux  1 , Franziska Marx  1 , Ilja Gunkel  1 , Christoph Weder  2 , Stephen Schrettl  3
Affiliations

Mechanically robust supramolecular polymer co-assemblies

Julien Sautaux et al. Nat Commun. .

Abstract

Supramolecular polymers are formed through non-covalent, directional interactions between monomeric building blocks. The assembly of these materials is reversible, which enables functions such as healing, repair, or recycling. However, supramolecular polymers generally fail to match the mechanical properties of conventional commodity plastics. Here we demonstrate how strong, stiff, tough, and healable materials can be accessed through the combination of two metallosupramolecular polymers with complementary mechanical properties that feature the same metal-ligand complex as binding motif. Co-assembly yields materials with micro-phase separated hard and soft domains and the mechanical properties can be tailored by simply varying the ratio of the two constituents. On account of toughening and physical cross-linking effects, this approach affords materials that display higher strength, toughness, or failure strain than either metallosupramolecular polymer alone. The possibility to combine supramolecular building blocks in any ratio further permits access to compositionally graded objects with a spatially modulated mechanical behavior.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Structure of metallosupramolecular copolymers.
The individual metallosupramolecular polymers were assembled by combining Zn(NTf2)2 with (a) a trifunctional building block based on a 1,3,5-tris(alkyl)benzene core and three 2,6-bis(1′-methylbenzimidazolyl) pyridine (Mebip) ligands (TAB) or (b) a telechelic poly(ethylene-co-butylene) featuring two Mebip ligands (BKB). The co-assembly of different weight fractions of the two building blocks in the presence of stoichiometric amounts of zinc(II)bis(trifluoromethanesulfonyl)imide (Zn(NTf2)2) afforded metallosupramolecular copolymers TAB/BKB:Zn that feature a phase involving ligands of both monomers (purple) as well as domains of the individual TAB:Zn (orange) and BKB:Zn (blue) polymers.
Fig. 2
Fig. 2. Thermal, thermomechanical, and structural properties of the MSPs and their copolymers.
a Differential scanning calorimetry (DSC) traces (first heating), b dynamic mechanical analysis (DMA) traces, and c small-angle X-ray scattering (SAXS) profiles of the neat metallosupramolecular polymers TAB:Zn and BKB:Zn, as well as of the TAB/BKB:Zn copolymers with the indicated TAB/BKB weight ratio (wt/wt%). d Temperature-dependent SAXS profiles of TAB/BKB:Zn containing TAB and BKB in a 50/50 wt/wt% ratio recorded at 30 and 180 °C, after cooling from the melt (1 min at 280 °C) to 250 °C, and after cooling to 180 °C. Heating and cooling rates were 10 °C min–1. The DSC traces and scattering profiles are vertically shifted for clarity.
Fig. 3
Fig. 3. Mechanical properties of the two MSPs and their copolymers.
a, b Representative stress–strain curves of the metallosupramolecular polymers TAB:Zn, BKB:Zn, and their copolymers TAB/BKB:Zn with the indicated TAB/BKB weight ratio (wt/wt%). c Plots of the Young’s modulus (E), tensile strength (σf), and toughness (UT) of samples as a function of the weight fraction of BKB. Data represent averages of n = 3–7 individual measurements with standard deviation. d Ashby (materials selection) plot showing the Young’s moduli and tensile strengths of the MSPs and copolymers and the properties attainable with some elastomers and commodity polymers, .
Fig. 4
Fig. 4. Healing and MSP copolymers with variable mechanical properties.
a, b Stress–strain curves of pristine, damaged, and healed (a) TAB:Zn and (b) copolymers with a TAB/BKB ratio of 50:50 wt/wt%. c Comparison of the toughness of pristine, damaged, and healed samples of TAB:Zn and copolymers with a TAB/BKB ratio of 50:50 wt/wt% (error bars represent the standard deviation of n = 3–4 individual measurements). d Photographs of a welded sample containing parts with TAB:BKB ratios of 60:40 wt/wt% (stiff, red-dyed) and 10:90 wt/wt% (soft, yellow-dyed). The soft segment acts as a hinge. e A compositionally graded film of MSP copolymers with TAB:BKB ratios of 60:40 wt/wt% (stiff, red-dyed) and 10:90 wt/wt% (soft, yellow-dyed) features a mechanical property gradient and bends under load. f The modulus of the welded sample shown in (d) is lowest in the segment with a TAB:BKB ratio of 10:90 wt/wt% (yellow-dyed) and the photographs show how the sample fails in this part upon uniaxial tensile deformation.
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