Preparation Of Slide-ring Gel Containing Acylhydrazone Bond And Its Self-healing Properties

Self-healing materials could heal the internal and external crack automatically to extendits limited life. Thus, developing self-healing materials has become a hot research topic inmaterial field.Conventional polymer gels were often classified into chemical and physical gels:Chemical gels behave good stabilities and mechanical properties, but it could hardly self-heal;while physical gels show contrary. Fortunately, chemists have successfully achieved theself-healing dynamic covalent chemical gels by introducing dynamic covalent bonds intochemical gels. Dynamic covalent chemistry involves in a series of chemical reactions incovalent bonding based on thermodynamically reversible equilibrium. Its core concept isdynamic covalent bond, which is a relatively stable "weak interaction" and could undergoreversible reaction under mild conditions.Recently, slide-ring gel, a novel kind of polymer gel, has been developed. Itsfigure-of-eight cross-links which could slide along the polymer chains freely have solved thespatial inhomogeneity problem in the gels. Therefore, it exhibites excellent mechanicalstrength, swellability and deformability compared to the conventional polymer gels.In this paper a dynamic covalent bond, acylhydrazone bond, was introduced into thefigure-of-eight cross-links of the slide-ring gel, aiming at combining the self-healingproperties of the dynamic covalent chemical gels and high mechanical strength of theslide-ring gel, and to prepare a gel material both with self-haeling properties and highmechanical strengths. This paper’s main research work and results are as follows:1. The synthesis of polyrotaxane: A polyrotaxane whose complexation degree is19%,and the average relative molecular mass is about110,000was synthesized in three step using“threading” approach. Firstly, the two hydroxyl groups of the PEG(Mn=33,000) were oxidizedto carboxyl groups by TEMPO, affording HOOC-PEG-COOH, and the functionality is about95%; Secondly, the pseudopolyrotaxane was synthesized in water via host-guest complexationof HOOC-PEG-COOH and α-CD; Finally, with BOP as the catalyst, polyrotaxane wassynthesized by end-capping amidation reaction between the end-capping reagent, stericallyhindered amantadine, and COOH groups of PEG.2. The synthesis of crosslinkers: Acylhydrazone crosslinkers containing acylhydrazonebonds and with the two end groups as cyanuric chloride, epoxy, hydroxyl, imidazole, weredesigned and synthesized respectively. Those acylhydrazone crosslinkers with epoxy,hydroxyl, imidazole as end groups were successfully obtained and characterized. 3. The synthesis and self-healing property research of slide-ring gel:(1) A slide-ring gelwas synthesized using acylhydrazone crosslinkers with hydroxyl end groups, HDI andpolyrotaxane in one-pot reaction. However, the corresponding gel did not behave self-healingproperty, probably due to the low content of acylhydrazone bonds;(2) Another slide-ring gelwas synthesized by the crosslinking reaction between acylhydrazone crosslinkers withimidazoles end groups and polyrotaxanes. The higher mass fraction of the crosslinker is, thegreater hardness of the gel is. However, the mechanical strengths of the gel was not strongenough.