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.

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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...

This study focuses on the crystal growth mechanism and the critical nucleus size of the inclusion compound formed between poly­(ethylene oxide) and urea (PEO-U-IC) β spherulites crystallized from the melt. The surface nucleation mechanism during the crystal growth process is proposed based on the exponential dependence of the spherulite radial growth rate G on the negative reciprocal of product of the isothermal crystallization temperature multiplied by the degree of supercooling (−1/(T cΔT)). The radial growth rates G of PEO-U-IC β spherulites crystallized from the mixed melt with the gradual addition of the diluting agent N,N′-dimethyl urea (2MeU) were measured under a polarized optical microscope. On the basis of the first nucleation theorem proposed by Kashchiev, the critical secondary nucleus size n* during the surface nucleation is determined from the slope of linear fitting line of ln G versus ln x, where x is the mass fraction of urea in U/2MeU. The critical secondary nucleus consists of 3–9 entities with each entity of the inclusion compound crystal containing 1 urea and 1.5 ethylene oxide repeating units when the crystallization temperature ranges from 65 to 85 °C. The relationship that n* is proportional to 1/(ΔT)2 confirms that the critical secondary nuclei at the solid–melt interface are two-dimensional.

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