Multi-stimuli responsive and multi-functional oligoaniline-modified vitrimers

Abstract

Smart polymers have been playing indispensable roles in our lives. However, it is challenging to combine more than three stimuli-responses or functionalities into one polymer, not to mention integrating multi-stimuli responsivity and multi-functionality at the same time. Vitrimers, an emerging type of materials, are covalently crosslinked networks that can be reprocessed but are still infusible and insoluble. Herein, we show that simply introducing oligoaniline into a vitrimer results in a covalently crosslinked material that can respond to six different stimuli (heat, light, pH, voltage, metal ions and redox chemicals) and perform six functions (shape memory, welding, healing, recycling, electro-chromism and adsorption of metal ions). New properties, which cannot be found in either neat vitrimers or oligoanilines, are generated, including photo-heal-ability, photo-weldability, pH-induced shape memory, enhancement of the photo-thermal effect due to metal ions absorption and simultaneous multi-tasking operations. Furthermore, the material is low-cost and suitable for large-scale mass production.

Fig. 1. Polymer synthesis and characterization. (a) Synthesis of ACAT–vitrimer. (b) FTIR spectra of ACAT and ACAT–vitrimer. (c) An illustration of reversible transesterification. (d) Stress relaxation experiments of ACAT–vitrimer at different temperatures.

Fig. 2. Heat responses of ACAT–vitrimer due to the intrinsic malleable property of vitrimers. (a) Welding (I–II) at temperature above T _v (200 °C, oven), permanent reshaping (II–III) at temperatures above T _v (200 °C, oven), temporary reshaping (III and IV) above T _g but below T _v (80 °C, oven) and shape memory (IV and V) by reheating above T _g (80 °C, oven). The thickness of the vitrimer films used here was about 0.2 mm. (b) Demonstration of the recycling process (with a thickness of about 0.2 mm). (c) Stress–strain curves for the recycled and original films.

Fig. 3. Responsive properties of ACAT–vitrimer to redox chemicals and voltages. (a) Chemical redox response of ACAT–vitrimer. (b) Cyclic voltammetry curve of ACAT–vitrimer on FTO conducting glass measured in 0.5 M H₂SO₄ (a solution of H₂O and DMSO) at a scan rate of 50 mV s^–1. (c) Chronoamperometry curves when the anodic potential was switched between 0 V and 0.8 V (vs. Ag/AgCl) for 30 s at each step. (d) Transmittance spectra of ACAT–vitrimer film under different applied potentials in the range of 0 V to 0.8 V (vs. Ag/AgCl) for 30 s at each potential (inset: photographs of ACAT–vitrimer at voltages of 0 V and 0.8 V).

Fig. 4. Photo-thermal effect enabled welding and healing of ACAT–vitrimer by light. (a) The temperature increase of ACAT–vitrimer and film without ACAT (neat vitrimer) upon light irradiation. (b) Stress–strain curves of the original film and films welded for 15 s and 30 s (with a thickness of about 0.2 mm) with a ramp rate of 0.4 N min^–1 (inset: an illustration of the welding process. To obtain a robust connection, under light irradiation, the overlapping region was first manually compressed using a piece of quartz glass for 2 s and then the glass was removed, obtaining a pre-welded sample. Then the pre-welded film was directly exposed to IR light to get a robust connection). (c) Pictures of the welded films before and after stress–strain experiments (the thickness is about 0.2 mm). (d) Light-triggered (0.70 W cm^–2) healing of ACAT–vitrimer with scratch (top) healed by local irradiation for 5 s (top right) and needle pierced hole (bottom) similarly healed within 10 s. (e) Control experiments using direct heating of scratch and pierced hole microscale defects (180 °C for 10 min) of ACAT–vitrimer.

Fig. 5. The effect of metal ions absorption on the light-triggered properties and the pH response. (a) The photo-thermal effect of the films I, II, III and IV (referring to neat vitrimer, neat vitrimer after absorbing Cu(ii), ACAT–vitrimer and ACAT–vitrimer after absorbing Cu(ii), respectively), where the content of ACAT was 1 mol% and the absorption experiments were conducted in 3 mmol L^–1 copper(ii) acetate monohydrate/THF solution for 20 min. (b) The healing experiments of the films (from left to right, ACAT–vitrimer, ACAT–vitrimer swelled in 3 mmol L^–1 copper(ii) acetate monohydrate/THF solution for 20 min and ACAT–vitrimer). (c) Shape recovery of films I, II, III and IV (the thickness of each film is about 0.2 mm) at different light intensities. (d) Reversible doping/un-doping of ACAT–vitrimer. (e) Extension–contraction response of an ACAT–vitrimer film (the thickness before swelling is about 0.2 mm) with changes in pH (acid and base solutions were 1 M PTSA/THF solution and 1 M TEA/THF solution, respectively).

Fig. 6. Manipulation of light-triggered properties on the same ACAT–vitrimer construct. (a and b) Successive welding and shape memory controlled by light (the thickness of each film is about 0.2 mm before deformation). (c) Sequential manipulation of healing and shape memory on the same film (with a thickness of about 0.2 mm) by light. (d) Stress–strain curves of the original film, damaged film and healed film with a ramp rate of 0.4 N min^–1.

Fig. 7. New shape memory performances. (a) Shape change of a bilayer responsive to metal ions and acid. (b) Shape change of the bilayer in different pH. (c) The multiple shape memory construct by welding films A, B and C (representative of ACAT–vitrimer, ACAT–vitrimer swelled in 1 mmol L^–1 Cu(ii)/THF solution for 20 min and ACAT–vitrimer swelled in 3 mmol L^–1 Cu(ii)/THF solution for 20 min) together. The thickness of each film is about 0.2 mm before deforming and the irradiation time of the shape recovery process at different light intensities was 10 s.