High Toughness Polyurethane toward Artificial Muscles, Tuned by Mixing Dynamic Hard Domains

Abstract

Developing multiphase polyurethanes (PUs) with loosely packed domains containing dynamic linkages and appropriately crystallized soft phases composed of polycaprolactone diol (PCL) segments is effective for the trade-off between toughness and self-healing. Here, we proposed a new strategy based on mixed dynamic hard segments to achieve the goal and improve self-healing behavior and mechanical performance. The designed polyurethanes comprise a microphase-separated structure with polycaprolactone diol as soft segments, which are facilitated to store entropy energy under strain. The aromatic disulfides together with aliphatic chain extenders were selected as hard segments to adjust the hierarchical structures, including microphase separation and crystallinity. The reversible hydrogen bonds and disulfide bonds distributed in the polymer network contribute to enhancing stretchability and self-healing performance. In this research, the robust polyurethanes with uniform microphase separation structures and insufficient crystallinity were designed by mixing a dynamic hard domain, which exhibits the potential application in the field of flexible conductors and synthetic muscles; the recovery efficiency at 90 °C is 93.8% and the ultimate stress/strain are 18.7 ± 0.2 MPa/2253 ± 149.2%. This work confirmed that the feasibility of synthetic PUs by changing the mole ratio of dual chain extenders simply, which is also expected to inspire the related fields of engineering, may require polymers with excellent self-healing efficiency and extraordinary robustness simultaneously.

A high‐performance self‐healing polyurea material based on exchangeable aromatic disulfide

“…It has been experimentally and theoretically demonstrated that the hydrogen bonds between urea linkages are the primary force for microphase separation, motivating the stacking of hard segments to form hard microphases and having a significant impact on the macroscopic properties of the material as physical cross‐linking 16–18 . We could thus investigate the stacking of hard domains by observing the strength of hydrogen bonding in SPU samples with different APD content.…”

“…The absorption peak of “Free” CO groups without hydrogen bonding corresponds to the highest wavenumbers. Once the hydrogen bonds form, the bond distance of CO is elongated and the bonding force is weakened, which lead to the decrease of the stretching vibration frequency and eventually cause the position of CO vibration band to shift toward the low wavenumber 17 . “Disordered” CO groups shift to lower wavenumbers due to distribution of electrons for two‐dimensional structure of single ligand, while “Ordered” CO shift to the lowest wavenumbers for the three‐dimensional structure of bidentate ligand 4,16,19 .…”

Highly Stretchable Fatty Acid Chain-Dangled Thermoplastic Polyurethane Elastomers Enabled by H-Bonds and Molecular Chain Entanglements

“…1 The hard domains of TPU could be formed based on different interactions such as π−π stacking and hydrogen bonds (H-bonds). 2,3 The soft segments are often composed of supple alkyl long chains. Therefore, TPU tends to exhibit a multiphase separation structure owing to the thermodynamic incompatibility between soft and hard segments.…”

“…Thermoplastic polyurethane (TPU) elastomer, as a kind of block copolymer which consists of alternate soft and hard segments, is extensively investigated because of the flexible design of its molecular structure and stable mechanical properties . The hard domains of TPU could be formed based on different interactions such as π–π stacking and hydrogen bonds (H-bonds). , The soft segments are often composed of supple alkyl long chains. Therefore, TPU tends to exhibit a multiphase separation structure owing to the thermodynamic incompatibility between soft and hard segments.…”

Synthesis of high-modulus thermoset PUs of PCL-PTMG/CNW biomaterials with different soft domain architecture and composition for high shape memory performance

“…The characteristic isocyanate bands, which are -N = C = O asymmetric stretch at 2272 cm − 1 and symmetric stretch at 1443 cm − 1 are absent in the spectrum as an indication of complete consumption of the functionality. Based on the images, the polyurethane bands are as follows: -NH-(amide I 1732 cm − 1 , amide II 1530 cm − 1 , amide III 1303 cm − 1 ), Ester υ(C = O) (urethane amide I υ(C = O) 1732 cm − 1 , δ(CH 2 ) :1443 cm − 1 and δ(CH) (urethane amide III 1249)(Ha et al, 2019;Qu et al, 2021). The band related to the ester carbonyl group is not available in the Raman spectrum of the PTMG-tPU and its intensity for the other three tPU specimens is lower than that of PCL-tPU.…”