Tuning Microphase Separation, Thermal Characteristics, and Physicomechanical Properties of Shape Memory Polyurethanes by Incorporation of Isocyanate‐Modified Fe₃O₄ Magnetic Nanoparticles

Abstract

Fe 3 O 4 magnetic nanoparticles (MNPs) are subsequently modified with (3-aminopropyl) triethoxysilane (APTES) and octadecyl isocyanate (OD) to yield MNPs-g-OD. Fourier-transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM) verified successful modification of MNPs with three different ratios of OD. Shape memory polyurethane (SMPU) nanocomposites containing 4 wt% of the neat, APTES-grafted, and OD-grafted MNPs are prepared through solution casting, where a strong correlation is achieved between the microstructure, crystallinity, thermal, and mechanical properties of the nanocomposites. Phase mixing degree of the soft and hard phases is increased by hydrogen bonding between the OD and polyurethane (PU) chains, causing to decrease of crystallization ability of PU chains. Field-emission scanning electron microscopy (FE-SEM) images show that high dispersion of MNPs-g-OD reduces the number and size of their aggregation sites in the PU matrix. The nanocomposites show high Young's modulus, because of increasing hydrogen bonding index of carbonyl groups with incorporation of MNPs-g-OD into the PU matrix. The nanocomposites show lower Young's modulus with increasing the degree of crystallinity. Shape memory studies indicated that all the samples have considerable shape memory abilities at 50 °C and room temperature. However, shape fixity ratios show a close dependence on the degree of crystallinity at room temperature.

Synthesis of dual‐stimuli‐responsive polyurethane shape memory nanocomposites incorporating isocyanate‐functionalized Fe3O4 nanoparticles

“…However, extra peaks could be observed at 2ϴ = 30.1, 35.5, and 43.2°. According to our previous study, 26 these diffraction peaks are respectively attributed to the (220), (311), and (400) crystalline planes of the OD‐ g ‐MNPs. It is noteworthy that due to the low content of hard segments and their insufficient orderliness to form crystals, the crystalline diffraction peaks assigned to hard segments could not be detected in the XRD patterns of PU and its nanocomposites 29 …”

“…The mechanical properties of the PU nanocomposites were studied both at room temperature and 50°C, and the results were reported in Figure 6. According to our previous studies, 26,34,37 the mechanical properties of the PU nanocomposites are mainly affected by the degree of crystallinity of PCL segments, nanofiller content, hard segment contents, and HBI CO . To reduce the controlling parameters of the mechanical properties, the OD‐grafted MNPs/PU nanocomposites were tested at 50°C.…”

“… 27 The presence of APTES groups on the APTES‐grafted MNPs could be confirmed by the absorption bands appeared at 3430 cm −1 (NH 2 ), 800–1200 cm −1 (SiOSi and SiOH), 700–800 cm −1 (CN), and 1462 and 2850–2920 cm −1 (CH; Figure 1d). 26,27 The reactivity of amine end groups of APTES‐grafted MNPs with isocyanate groups of OD was used for the subsequent modification of the MNPs (Figure 1c). The appearance of –NH stretching vibration (3340 cm −1 ), CH bending and stretching vibrations (1467 and 2850–2920 cm −1 ), and free and hydrogen‐bonded urea CO bands (1570–1615 cm −1 ) in FTIR spectrum of OD‐grafted MNPs (Figure 1d) demonstrates the successful functionalization process 26,28 .…”

“… 26,27 The reactivity of amine end groups of APTES‐grafted MNPs with isocyanate groups of OD was used for the subsequent modification of the MNPs (Figure 1c). The appearance of –NH stretching vibration (3340 cm −1 ), CH bending and stretching vibrations (1467 and 2850–2920 cm −1 ), and free and hydrogen‐bonded urea CO bands (1570–1615 cm −1 ) in FTIR spectrum of OD‐grafted MNPs (Figure 1d) demonstrates the successful functionalization process 26,28 . Comparison of FTIR spectra of the PU nanocomposites and pristine PU (Figure 1e) indicates that the incorporation of the OD‐grafted MNPs has not affected the chemical interactions between PU chains 29 …”

“…However, their surface modification with hydrocarbon chains could improve their interaction with organic materials. Therefore, OD‐grafted MNPs could appropriately disperse in PU matrix at lower contents 26 . However, despite the high interactions of OD‐grafted MNPs with PU chains, they could accumulate in PU matrix at higher contents due to the strong dipole–dipole magnetic interactions between MNPs.…”