Polyurethanes with covalent adaptable networks (CANs) have received extensive attention due to their recyclability and selfhealability; meanwhile, how to design and regulate the structure and properties of dynamically cross-linked polyurethanes with biobased monomers is of particular interest. Herein, we design a new type of dynamically cross-linked polyurethane derived from biobased polyol (castor oil) and industrial bulk products: bisphenol and isophorone diisocyanate. Furthermore, we develop a strategy to regulate the rearrangement kinetics of the dynamic covalent networks. The stronger the electron-withdrawing effect of the structure between the two benzene rings in bisphenol, the easier the network rearrangement and the lower the initial temperature of dynamic bonds dissociation. By varying the type and ratio of mixed bisphenols, the initial temperature of dynamic bond disassociation and the rate of network rearrangement can be adjusted within a wide range. In addition, by changing the cross-linking degree, the mechanical properties, glass-transition temperature, and network rearrangement rate can also be tuned. In this work, we have established a new method for designing biobased polyurethanes with CANs, which is beneficial for developing self-healing and recyclable cross-linked polyurethanes with variable properties from biobased feedstock and industrial bulk products.

Four linear polyurea elastomers synthesized from two different diisocyanates, two different chain extenders and a common aliphatic amine-terminated polyether were used as models to investigate the effects of both diisocyanate structure and aromatic disulfide chain extender on hard segmental packing and self-healing ability. Both direct investigation on hard segments and indirect investigation on chain mobility and soft segmental dynamics were carried out to compare the levels of hard segmental packing, leading to agreed conclusions that correlated well with the self-healing abilities of the polyureas. Both diisocyanate structure and disulfide bonds had significant effects on hard segmental packing and self-healing property. Diisocyanate structure had more pronounced effect than disulfide bonds. Bulky alicyclic isophorone diisocyanate (IPDI) resulted in looser hard segmental packing than linear aliphatic hexamethylene diisocyanate (HDI), whereas a disulfide chain extender also promoted self-healing ability through loosening of hard segmental packing compared to its C-C counterpart. The polyurea synthesized from IPDI and the disulfide chain extender exhibited the best self-healing ability among the four polyureas because it had the highest chain mobility ascribed to the loosest hard segmental packing. Therefore, a combination of bulky alicyclic diisocyanate and disulfide chain extender is recommended for the design of self-healing polyurea elastomers.

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Polyurethanes with covalent adaptive network (CAN) have received widespread attention due to their recyclability and self-healing properties. The strategy of regulating the dynamic network rearrangement kinetics through varying the monomer...

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Polyureas are known for their remarkable toughness, which originates from the nanoscale segregated morphology and hydrogen bonding between urea groups. However, the underlying molecular mechanism of how the microscopic structure results in the macroscopic toughness is not fully understood. In this work, the mechanical response and microstructural evolution of a model polyurea under uniaxial deformation were investigated via nonequilibrium molecular dynamics simulations based on a hybrid all-atom/coarse-grained model. The stress–strain curve obtained from the simulation captured the key features of the nonlinear mechanical response of polyureas. The structural evolution was characterized by the microscopic strain and stress as well as statistics of the hard-domain structure and segment conformations. Two distinct molecular mechanisms were identified: self-reinforcement by oriented hard segments and stress-adaptive release of soft segments. Through these mechanisms, the evolution of microscopic structure was related to the macroscopic toughening of polyureas, shedding light on the development of better materials.

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Flexible polymers are widely used in the fields of wearable devices, soft robots, sensors, and other flexible electronics. Combining high strength and elasticity, electrical conductivity, self-healability, and surface tunable properties...