The Construction And Mechanism Study On Tough Gels With Self-healing Properties

Polymer gels are composed of macromolecular polymer with three-dimensional networks and a large amount of solvent. It have a lot of excellent properties, such as good biocompatibility, super water-absorbing quality, environmental responsiveness and antibacterial property et al. Because of the superior properties, the gels have an extensive application in medicine, biomedical sciences, industries, agriculture and architecture.However, pHysical crosslinked gels have good self-healing properties, but poor stability and mechanical strength. By contrast, chemical crosslinked gels have good stability and mechanical strength, but poor self-healing ability. Integrating the self-healing properties of the pHysical crosslinked gels and the chemical crosslinked gels with stability and mechanical strength into a single system to yield a robust but smart gel is difficult and a frontier research in the field of gel.PEO-PPO-PEO three-block polymers have excellent self-assembly properties, they can form micelles on low concentration or form pHysical crosslinked micelles with high concentration.Dynamic covalent bonds are reversible. Therefor it can undergo reversible breaking and reformation under equilibrium conditions. Polymers gels employ the reversible covalent bonds to enhance its mechanical strength and achieve self-healing properties through controlling the exchange reaction.This research combines dynamic covalent bonds and PEO-PPO-PEO three-block polymers to form self-healing gels with high mechanical strength properties of pHysical crosslinked gels and good stability of chemical crosslinked gels.The main research contents and results of this paper are as follows:The synthesis of gelators: those synthesis through esterification, nucleopHilic substitution and hydrazinolysis et al. After modifying terminus of PEO-PPO-PEO three-block polymers(Pluronic F127, Mn=12600), 3-armed PEO(Mn=3000) and PEO(Mn=2000) respectively, Finally, aldehyde-terminated PF127 three-block polymers and acylhydrazine-terminated 3-armed PEO or PEO were synthesized respectively with more than 95% terminal functionality ratio.The exploration of gels’ preparation conditions. Dynamic polymer gels were synthesized by condensation of aldehyde-terminated PF127 three-block chain polymers(Mn=12600)and acylhydrazine-terminated 3-armed PEO(Mn=3000) in disodium hydrogen pHospHate and sodium dihydrogen pHospHate buffered solution. The concentration of gelators, type of solvents, and pH of buffered solution have influence on gels’ preparation. When increasing the concentration of gelators, the time to prepare gels can reduce. Gels would shrink under water solvent, while it’s difficult to prepare gels in organic solvents. The cross-linking rate is too low when preparing gels in pH=7 buffered solution. Only when the concentration of gelators increased to 15 percent, as well as the pH=6 of the disodium hydrogen pHospHate and sodium dihydrogen pHospHate buffered solution, gels would achieve the best condition with high mechanical strength.Research on mechanical strength of gels. the research combined IR test,rheological test, tensile test, loading-unloading tensile test with different recovery time, tear test, crack test and swelling test of mature gels, the results showed tensile intensity is 0.3MPa and tensile elongation is 120 times of the gels, which was prepared in pH=6disodium hydrogen pHospHate and sodium dihydrogen pHospHate buffered solution and the concentration is 15 percent. This gels can not be teared.The research on the formation mechanism of the high mechanical properties of the gels.Through the comparison experiments, the gels made only by single-acylhydrazone bonds or physical crosslinked micelles are worse than gels made by both of them in mechanical properties. Therefore, we conclude that the high mechanical properties of the gels is due to the synergistic effect of acylhydrazone bond and pHysical crosslinked micelles.The Research on self-healing properties of gels. The acylhydrazone bonds, which was reversible and dynamic, were formed under mild conditions with acidic catalysis and the gels are cross-linked by acylhydrazone bonds. When two plates of gels were contacted together, they can self-heal and merge together after 24 hours. The self-healed gels have similar tensile intensity and tensile elongation as the original gels.