Super self-healing properties of ultra-soft materials

Dynamic covalent bonds can be reversibly broken or formed under certain conditions, it may be used to control the cross-linked polymer with a viscoelastic purposes. At present, despite the great efforts have been made to develop new dynamic and chemical bonding of the catalyst to promote a variety of stimuli covalently adaptive network (CAN, covalent adaptable networks) exchange reaction in, but few studies have addressed other design factors can affect the material properties of conventional polymers. bottle brush polymers (bottlebrush polymers) is a covalent network adaptation ideal material because they can widen the available range of polymer physical properties. When physical or chemical bond with other substances elastic crosslinking, polymer non-dynamic network, since the networks and entanglement is reduced network density, the resulting bottle brush polymers abnormal soft elastomer, such flexibility in many emerging applications capacitive pressure sensor of high sensitivity, high dielectric actuator biomimetic materials and the like has advantages. However, bottle brush polymers typically by non-covalent cross-linking dynamically, these conventional methods can not achieve self-repair of the material, which is critical to reduce damage to the equipment or an analog bioremediation process.

the results of

Based on the above issue, Department of Materials, University of California, Department of Chemistry and Biochemistry and the Department of Chemical Engineering Professor Christopher M. Bates research group [123 ], we introduced a powerful synthetic platform that combines the advantages of the molecular architecture and adaptive covalent network, can be synthesized bottle the dynamic crosslinking ultra soft properties can be reconfigured by associative exchange key brush polymeric elastomer , these dynamic bottle brush polymers exhibit elastic> elongation at break of 300%, and still retain> 85% of the fracture toughness and after repeated annealing. Related outcomes to \”Dynamic Bottlebrush Polymer Networks: Self-Healing in Super-Soft Materials\” in the title, published in the \” JACS \”.

Graphic SolutionsAnalysis of the reaction scheme

1. Design and Synthesis of

超软材料的超强自修复性能 FIG dynamic toothbrush polymer network is dynamic key exchange [123 ]
researchers design choice bottle brush with the polyester side chain polymer covalently adaptive network for dynamic association by transesterification as a covalent bond exchange system model (Figure 1). P4MCL macromonomer by ring-opening polymerization is first prepared by the reaction, and then by ring-opening metathesis polymerization (ROMP) further polymerizing the macromer to bottle brush polymers. From a single batch macromers, by changing the magnitude of Grubbs catalyst when synthesizing a
different main-chain degree of polymerization (the NBB)

a plurality of unique bottle brush polymers. Finally, with a diketone P4MCL hydroxyl side chain end and a Lewis acid catalyst, of the bottle brush crosslinked polymer precursor. The catalyst used in this step is retained after cross-linking in the material, and to facilitate dynamic key exchange by transesterification. 2. The characteristics of dynamic covalent bond

Stress relaxation experiments FIG. 2 shows that the samples 1A, P4MCL Toothbrush networks are dynamic at high temperatures. White dotted line represents the fitted exponential decay (eq S1). (A) a crosslinking agent and a constant load against the temperature dependency (ncl = 10) at. (B) the cross-linking agent loading at a constant temperature (160 ° C) of. (C) Relaxation Arrhenius behavior; Arrhenius equation for a broken line 超软材料的超强自修复性能
First, the establishment of various formulations of researchers 1A (NSC (side chain absolute degree of polymerization) = 47, NBB = 54) of the toothbrush network P4MCL dynamic characteristics. At high temperatures (160-180 ° C, FIG. 2) all three samples exhibited significant stress relaxation. This rate increases with temperature increases (FIG. 2a), but with NCL (amount of crosslinking agent) 2 increase (FIG. 2b). Further analysis shows, lnτ * T-1 with a linear Arrhenius dependence, as shown in Figure 2c, it is very common for network association dynamic key exchange.

3. Mechanical properties

FIG. 3 P4MCL toothbrush polymerizationCAN is ultra-soft material, at a temperature lower than the dynamic exchange start (T = 25 ° C) storage modulus having adjustable. (A) a 1B, 2B, 3B and 4B ncl = frequency sweep resulting formulation 25 (closed symbols: storage modulus; open symbols: loss modulus). P4MCL comprising a linear network for comparison. Frequency sweep (c) (b) by changing the recipe from ncl toothbrush for polymer 2B (NBB = 180) generates low-frequency stable modulus (Gx, bottlebrush) / linear proportional relationship with the ρncl Mn. 超软材料的超强自修复性能
Next, the macromonomer B (NSC = 33, NBB = 53, ncl = 25) obtained four samples were cured in a mold, tested for mechanical properties to show an adjustable toothbrush of CAN P4MCL (FIG. 3a). When NBB ncl increases at a constant value, since the reduced cross-linking density, Gx, bottlebrush reduced. Even under conditions ncl = 25, the length of the toothbrush precursor (NBB = 380) still produces a soft material to 15 kPa at 25 ° C. Load also determines the amount of crosslinking agent Gx, bottlebrush. Ncl will become 45, Gx, bottlebrush variation (FIG. 4b) between 8 and 62 kPa. In general, much smaller than the modulus of the linear module generates CAN network construction, and more typically in a highly solvated hydrogel or organogel. Dynamic bottle brush-like structure of the polymer network – quantitative attributes will allow understanding of the relationship between specific modulus, eliminating the need for cumbersome Edisonian optimization. For the four different combinations below a threshold value ρncl / Mn of NBB and the NSC, in Figure 3c the relationship is still valid, when the threshold is exceeded, the crosslinking agent is not completely dissolved in a given bottle brush polymers.

4. Healing and cyclability

FIG 4 uniaxial stretching and self-healing experiments demonstrate scalability of CAN polymer toothbrush P4MCL (sample 2B: NSC = 33, NBB = 180; ncl = 15). After three cycles, to recover the toughness of> 85%. 超软材料的超强自修复性能
Finally, intermediate backbone length load network and a crosslinking study P4MCL toothbrush polymer CAN scalability and recyclability (FIG. 4). Three experiments performed on the uniaxially stretched, in all cases, the measured strain at break had similar values ​​(325-350%) and toughness (recovery rate> 85%). These studies highlight the self-healing from a bottle brush and recyclability covalent polymeric elastomer adaptive network.
summed

In summary, researchers have introduced a new covalent adaptive network (the CAN), the polymer network includes a brush member carried by the bottle associated dynamic key exchange mechanism. Such dynamic network will find useful application in the self-healing properties of ultra-soft combination, such as next-generation sensors, drives and organizational simulation of biological material. The scope of covalent adaptive network expanded to include non-linear molecular structure, will create new opportunities in cross fields of chemistry, materials science and engineering. Article link: https: //pubs.acs.org/doi/10.1021/jacs.0c01467

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