Elaborate fabrication of well-defined side-chain liquid crystalline polyurethane networks with triple-shape memory capacity

Abstract

a Target to triple-shape memory capacity, a series of side-chain liquid crystalline polyurethane networks (SCLCPU-Ns) with well-defined architecture are prepared via an elaborately designed synthetic route: polymerizing the liquid-crystalline (LC) founctionalized monomer with diisocyanate to produce linear polyurethane precursor with uniform distribution of pendant mesogenic units; and then, using tetra-functional pentaerythritol (PTOL) as the crosslinker to produce the PU network with similar backbone length between each crosslinking point. The chemical structures of monomer and linear polyurethane precursor are characterized by nuclear magnetic resonance (NMR). The differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide angle X-ray (WAXD) are employed to verify the nematic nature of liquid crystalline state. DSC analysis combined POM observation reveals that almost all SCLCPU-Ns display two thermal transitions (Tg and Tcl), which can be utilized as Ttrans to trigger the triple shape memory behavior. The cyclic thermomechanical analysis performed by DMA reveals that the networks exhibit excellent triple-shape memory properties, although the architecture of the networks influences their performance. Taking advantage of the overlap of Tg and Tcl in SCLCPU-Ns, which can be regarded as one broad thermal transition, a well-controllable gradual recovering process has been realized in a broad termperature range.

A Review on Liquid Crystal Polymers in Free-Standing Reversible Shape Memory Materials

“…The basic principle behind the shape change of LCPs depends on alignment directions and relevant phase transitions (nematic, cholesteric, smectic, or isotropic) [3]. The majority of studies on the actuation of LCPs based on thermally induced order-disorder phase transition are illustrated in Figure 1a [2,12]. Materials exhibit anisotropic deformation along the director orientation as the order parameter (S) change above the phase transition temperature.…”

Biodegradable shape memory polyurethanes with controllable trigger temperature

“…For a thermally induced SMP, its thermal properties, especially the transition temperature associated with the switching domains play an important role for the triggering of shape recovery [38] . Figure 1 presents the third heating traces of PCLAs at a heating rate of 10 K/min.…”

Unique two-way free-standing thermo- and photo-responsive shape memory azobenzene-containing polyurethane liquid crystal network

“…The shape memory experiment was conducted as described previously [28,57], where the experiment was performed on a DMA Q800 (TA Instruments, USA) under controlled force mode. The testing program is available in the Supplementary information.…”