A multistimuli-responsive fluorescent polymer gel based on thioctic acid and hyperbranched polymer

Fluorescent gels with fast and reversible responses have attracted extensive attention, but it remains a huge challenge to synthesize high performance multistimuli-responsive fluorescent gel through a facile and versatile approach. In this work, a multistimuli-responsive fluorescent thioctic acid-crosslinked hyperbranched polymer gel (TLHP) was designed and fabricated by copolymerization of acrylic acid, amino-ended hyperbranched polymers (AHP), tetrakis(4-aminophenyl)ethene (TPE-4NH2) and thioctic acid (TA). The structures of the TLHP gel were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). AHP played an important role in the TLHP gel. The terminal amino groups of AHP and TPE-4NH2 in the network served as strong complexing centers with carboxylic groups of TA and acrylic acid by hydrogen bonding interactions, thus a unique toughening and self-healing strategy for the supramolecular network was established. Compared with poly(TA and acrylic acid) (TPAA), TLHP-0.4 % which incorporated 0.4% TPE-4NH2 exhibited excellent mechanical properties, with tensile strength up to 438 kPa and stretchability up to 741 %, increased by 193.3 % and 45.3 %, respectively. In addition, TLHP-0.4 % was crosslinked through the dynamic covalent disulfide bonds and the noncovalent H-bonds between amino or carboxy groups, and exhibited fluorescence responsiveness to temperature, pH, and metal ions, greatly expanding the application of TLHP as rewritable printing ink and temperature-based erasing. The fluorescence of TLHP was also sensitive to Cu2+, and the intensity can be restored by EDTA solution to realize fluorescence "switching". The multistimuli-responsive fluorescence of TLHP may have broad prospects in reversible patterning displays, multi-level anti-counterfeiting applications for information security, and various potential applications.