Tunable and Processable Shape-Memory Materials Based on Solvent-Free, Catalyst-Free Polycondensation between Formaldehyde and Diamine at Room Temperature

Abstract

Compared with traditional thermosets, malleable thermosets have more applications in aerospace, biotechnology, and construction. Here we report a one-step, solvent-free, catalyst-free polycondensation method between diamine and formaldehyde to prepare a series of malleable hemiaminal dynamic covalent networks (HDCNs). The materials have excellent malleability and reprocessability by hot pressing. The Young's modulus and breaking strength of HDCNs obtained by the polycondensation of formaldehyde and 4,4-diaminodiphenylmethane (MDA) are as high as 1.6 GPa and 60 MPa, respectively, which can be facilely adjusted through the introduction of polyetheramine-400 (PEDA). Moreover, the HDCNs feature the shape memory ability with a recovery ratio above 93.5% and can be recycled by the addition of different monomers. This promising HDCN, prepared from economical raw materials, may have vast applications in industries.

Reprocessable, Reworkable, and Mechanochromic Polyhexahydrotriazine Thermoset with Multiple Stimulus Responsiveness

“…Similar to the reported method by Yuan et al [ 41 ], the specimens for thermal and mechanical tests were prepared as illustrated in Figure 1 b. Since both the disulfide bond and hemiaminal group are dynamic covalent bonds [ 50 , 51 ], uniform coherent PHT bars could be obtained by pressing HDCN powders at 150 °C under 0.3 MPa for 1 h. It should be noted that the PHT specimens were prepared by a hot-press process rather than direct curing in a mold. This is because there exists a high boiling point NMP solvent in the monomer mixture.…”

Dynamic covalent polymers for biomedical applications

“…Dynamic covalent polymers have thus been shown to demonstrate many unique properties, such as self-healing ability, recyclability, stimuli-responsiveness, shape memory behavior, degradability, etc., which will be discussed in the following sections. [51][52][53][54][55][56][57]…”

Vitrimer-Like Shape Memory Polymers: Characterization and Applications in Reshaping and Manufacturing

“…A combination of the vitrimer-like behavior and SME enables many new ways to manipulate polymers, far beyond folding/unfolding, reprocessing and heating assisted healing, which have been focused on in most of the studies reported so far [ 21 , 25 , 26 ]. In this section, in addition to these well-known applications, we explore some more possibilities in reshaping (inside/outside, microscopically/macroscopically, permanent/temporary) and manufacturing using vitrimer-like SMPs and their composites.…”

“…In recent years, many new types of vitrimers have been invented via different approaches for enhanced performance and/or for some special features (such as, the novel SME or self-folding/unfolding [ 21 , 22 , 23 , 24 , 25 ], i.e., reshaping), malleability and reprocessability by hot-pressing (i.e., associated with recycling as thermo-plastics) and heat-assisted healing, etc., [ 21 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Current methods to characterize vitrimers are mostly based on the Arrhenius law [ 17 , 33 , 35 ].…”