Synthesis Of UPy-based Supramolecular Polymers And Their Stimuli-responsive Materials

Based on supramolecular chemistry,the idea of utilizing non-covalent interactions to establish functional structures provides abundant inspiration and infinite possibilities for the design and synthesis of sophisticated stimuli-responsive materials.Combining the knowledge of traditional polymer chemistry and emerging supramolecular chemistry,depending on the requirements of multiple functions,the designing and preparing of supramolecular polymer materials and attaining well-defined supramolecular structures have been a research hotspot in the field of functional materials.Numerous researchers focus on exploring supramolecular interactions,while simultaneously advancing the application and development of supramolecular materials science in the fields of electronics,healthcare devices,biomedicine,environment and energy.In this research,the prominent dynamic reversible 2-ureido-4[1H]-pyrimidinone(UPy)quadruple hydrogen-bonding motif was employed to construct responsive supramolecular polymer materials that can meet specific needs and promote them to electronic devices and medical and health fields.The main research contents are as follows:According to the application in the low temperature and underwater environment of the electronic device with fast self-healing properties,the dynamic reversible and thermal responsive UPy units were used to synthesize two kinds of supramolecular polymers with different T_m.Based on their dilute solution property,the mixture of supramolecular polymer was obtained.Studying the relationship between the different mixing proportion and self-healing temperature,a novel supramolecular polymer material(SPM),which maintained a good mechanical property at room temperature and represented self-healing behavior in low temperature(33-34?),was finally obtained.Multi-walled carbon nanotubes(MWCNTs)were"implanted"into the SPM substrate as a functional coating by using air spraying method of MWCNTs/CHCl₃ dispersion,which endows the SPM film with a good conductivity,photo-thermal conversion and adhesion.The thermal and mechanical responsive flexible sensors were fabricated by the MWCNTs/SPM films,which were used as physiological motion and vital signs monitoring equipment.Due to the hydrophobicity of the SPM matrixes and MWCNTs,the sensor exhibited highly efficient self-healing properties in underwater environments by non-contact NIR actuation.It is challenging to prepare the hydrogel devoted to fabricate a form of multi-responsive skin-like sensor piggybacked on the tactile controlled robot which could grab the soft and fragile items at subzero temperatures.The supramolecular ionic liquid hydrogel,wherein ureidopyrimidinone(UPy)containing hydrophilic polyurethane(PU)was employed as networks and aqueous solutions of imidazolium ionic liquid acted as free phase.Combining the advantages of hydrophilic PEG segments,the hydrophobic UPy moieties,and the imidazolium ionic liquid,this supramolecular hydrogel exhibited high water content(?86%),swelling ratios(?485%),elongation(?750%),low resistivity(0.51 k?·cm)and excellent transparency(?98%).Moreover,the most striking characteristic was that the supramolecular hydrogel maintained its outstanding mechanical and thermal sensitivity at subzero temperatures such as-20?.The supramolecular ionic liquid hydrogel was utilized to fabricate E-skin for intelligent robots to realize pressure feedback and thermal recognition.This line of research not only demonstrates that the anti-freezing stimuli-responsive hydrogel is a promising candidate for E-skins used in harsh conditions,but also contributes to the design and application of supramolecular polymers-based hydrogel sensors for future artificial intelligence applications.Based on the above,UPy derivatives,as chain extenders,were introduced into the side chain to structure supramolecular polymer.Through the hydrophilic PEG segments in main chain,the supramolecular polymer matrixes were swelled into hydrogel.Meanwhile,due to the hydrophilic and hydrophobic differences between the main chain PEG segments and the side chain UPy units,as well as t thermal-responsiveness of UPy groups,the supramolecular polymer hydrogel(SPH)represented phase transition during heating,which resulted in the material's color whitening and volume shrinkage in macroscopic view.In this study,the mechanism of phase transformation in the system was investigated in detail.It is indicated SPH with PEG(M_W?1000)had an obvious phase transition temperature close to the physiological temperature of the human body,which has vast potential application value of biomedical materials.Utilizing SPH as bio-dressings,the drug loading and in vitro release experiments were carried out demonstrating that the cumulative drug release in simulated human body temperature environment(37?)was higher than that at room temperature(20?),and the phase transformation behavior of SPH drugs carrier partly contributed to it.