Abstract
In this study, 4,4′-diphenylmethane diisocyanate and polytetramethylene glycol were used to prepare a prepolymer; N,N′-bis(4-hydroxybenzylidene)-2,6-diaminopyridine (BHBP) was used as a chain extender; and these elements were combined to prepare a novel polyurethane, BHBP/PU. Gel permeation chromatography revealed that the molecular weight of the BHBP/PU samples increased as the BHBP content was increased. Fourier transform infrared spectroscopy demonstrated that high BHBP content facilitated strong hydrogen bonding in the samples. Differential thermogravimetry indicated that the initial decomposition temperature of BHBP/PU-3 was approximately 10 °C higher than that of BHBP/PU-1. Differential scanning calorimetry and dynamic mechanical analysis revealed that increasing the BHBP content substantially increased both the glass transition and dynamic glass transition temperatures of the BHBP/PU samples. The tensile strengths of BHBP/PU-1, BHBP/PU-2, and BHBP/PU-3 were 7.7, 10.9, and 21.6 MPa, respectively, with corresponding Young’s moduli of 0.7, 1.9, and 3.3 MPa. These results demonstrated that both the tensile strength and Young’s modulus of the BHBP/PU samples increased as the BHBP content was increased. Moreover, the BHBP/PU samples exhibited excellent shape recovery of >90%.
Highlights
Polyurethanes (PUs) were first discovered by Otto Bayer in the 1940s [1]
In thermally induced Shape-memory polymers (SMPs), the thermoreversible phase that serves as a ‘switch’ is the transition between the glass transition temperature (Tg) and the melting point (Tm) [12]
Altering the soft and hard segments of the polytetramethylene glycol (PTMG) and the BHBP content, this study investigated the thermal properties, mechanical properties, shape recovery, and moisture sensitivity of the BHBP/ PU polymers
Summary
Polyurethanes (PUs) were first discovered by Otto Bayer in the 1940s [1]. Since their discovery, PUs have increasingly attracted attention because of their wide range of industrial applications such as in shipbuilding, automobiles, footwear, and construction [2,3]. The effect of ambient temperature on these hydrogen bonds enabled 90% shape memory of the PUs. The pyridine-containing supramolecular PUs synthesized in [22] used the nitrogen atoms in the pyridine to facilitate hydrogen bonding with urethane segments. The pyridine-containing supramolecular PUs synthesized in [22] used the nitrogen atoms in the pyridine to facilitate hydrogen bonding with urethane segments These hydrogen bonds served as the molecular switch and enabled the shape-memory effect of the PUs. Some other studies have introduced highly functional pyridine rings to polymers through chemical synthesis. 2,6-diaminopyridine and 4-hydroxybenzaldehyde were synthesized to obtain the pyridine-containing chain extender N,N′-bis(4hydroxybenzylidene)-2,6-diaminopyridine (BHBP) Both the nitrogen atoms of pyridyl and imine groups in BHBP units can form hydrogen bondings with N-H groups in the PU units theoretically. Altering the soft and hard segments of the PTMG and the BHBP content, this study investigated the thermal properties, mechanical properties, shape recovery, and moisture sensitivity of the BHBP/ PU polymers
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