Physio- and chemo-dual crosslinking toward thermoand photo-response of azobenzene-containing liquid crystalline polyester

Abstract

Combining the stability of chemical crosslinking and the processability of physical crosslinking is a well-established strategy to design new materials with desirable stimuli-responsive properties. Herein, a series of azobenzenebased thermotropic liquid crystalline polyesters were synthesized by introducing mesogenic dial named 4,4ʹ-bis(6-hydroxyhexyloxy)azobenzene (BHHAB), 2-phenylsuccinic acid (PSA), and different contents of 1,2,3-propanetricarboxylic acid (PTA) as the chemical crosslinker. All these polyesters showed good thermal stability and smectic liquid crystalline phase. Wide-angel X-ray diffraction (WAXD) and the fluorescence emission spectra confirmed the existence of π-π stacking interactions as the physical crosslinking in the polymer chains, particularly at the lower content of PTA. However, when the PTA content increased, the chemical crosslinking changed the chain conformation, and thus the intensity of physical crosslinking slackened gradually. Combining the physical and chemical crosslinking, these polyesters showed the thermoplastic processability, thermal shape memory, heat-assisted healing and photoresponsive behaviors. Taking advantages of these features, these multiple stimuli-responsive polymers can bring more chances for smart materials such as soft actuator.

Well-Tailored Dynamic Liquid Crystal Networks with Anionically Polymerized Styrene-Butadiene Rubbers toward Modulating Shape Memory and Self-Healing Capacity

“…In recent studies, integrated networks incorporating permanent and dynamic crosslinks can not only ensure remarkable mechanical properties but also improve dynamic behaviors. , In this work, the effect of MW, the permanent HMDI, and dynamic UPy networks on shape memory was studied. As shown in Figure S15, the R f values (refer to eq 1 in the Supporting Information) of r -HSBR 20k - g -M and r -HSBR 45k - g -M were 87.9 and 78.2%, respectively, which were mainly attributed to the weak H-bonding interactions of -OH groups and the formation of orderly LC stacking in the cooling process.…”

“…Generally, self-healing ability is commonly limited to chain diffusion because the reformation of dynamic bonds requires molecular mobility, which indeed would sacrifice the mechanical strength . Meanwhile, the permanent covalent linkages improve the mechanical strength but sacrifice reprocessability . It seems necessary to combine permanent covalent linkages and dynamic bonds for further applications.…”

“…45 Meanwhile, the permanent covalent linkages improve the mechanical strength but sacrifice reprocessability. 46 It seems necessary to combine permanent covalent linkages and dynamic bonds for further applications. Therefore, an integrated design of LCNs with simultaneous mechanical enhancement and molecular mobility is required to meet the requirements of various applications.…”

Recent Advances in Functional Polyurethane Chemistry: From Structural Design to Applications

“…Azobenzene has also been used to construct lightresponsive shape memory polymers with wavelengths of 442 nm required for light-induced shape memory effects. [107] Du et al covalently combined functional graphene oxide into hydroxyl-terminated polyurethane and prepared polyurethane graphene oxide composite material containing diselenide bonds by in situ polymerization (Figure 8(a-c)). [108] The shape memory effect of the composite under near-infrared irradiation is attributed to the excellent photothermal and crystallization induction effects of functionalized graphene oxide (Figure 8d).…”

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

“…Apart from thermoresponsive LCPs, photo-responsive LCPs containing azobenzene mesogens have been widely used for fabricating shape-change actuators. Reversible trans-cis photoisomerization causes a tiny decrease in the order parameter of LCPs which contributes to shrinkage in the film surface, resulting in bending and unbending [17][18][19], twisting [20], oscillations [21], and three-dimensional (3D) movements [22,23]. Considering safety, high-energy UV light is not an ideal source for practical applications.…”