The Preparation And Performance Study On Tough DN-gels With Self-healing Properties

Polymer hydrogel is a new type of polymer material that contains a large amount of water inside a three-dimensional cross-linked polymer network.It has a wide range of uses in medicine,biology,agriculture,industry and other fields.Traditional hydrogels often have defects such as instability,poor mechanical strength,and short service life.How to make the hydrogel possess high mechanical properties and good self-healing properties at the same time is the current research hotspot.The traditional double network hydrogel has excellent mechanical properties.It is generally composed of two layers of networks:the first layer is a high-density crosslinked polyelectrolyte network as a rigid framework structure,and the second layer is filled in the polyelectrolyte network Sparsely cross-linked neutral polymer network.When subjected to external forces,the first layer of network will be broken and fractured as a"sacrificial network"to dissipate energy,while the second la yer of network will endow the gel with ductility and maintain its elasticity and shape.The energy dissipation mechanism of this two-layer network coordinated with each other greatly improves the mechanical properties of the hydrogel.However,after the first layer of network is broken during the deformation process,it cannot be repaired by itself.Therefore,the gel loses its effective energy dissipation mechanism,and its mechanical properties will be greatly damaged.This shortcoming restricts the application of dual network hydrogels.Aiming at this shortcoming,this thesis intends to introduce dynamic covalent bonds such as acylhydrazone bonds and oxime bonds into the two-network hydrogel,and cross-link with acylhydrazone bonds or oxime bonds to form the first layer of network,using their high strength and yet The advantage of dynamic reversibility enables the first-layer network to self-repair after being broken and rebuild the energy dissipation mechanism,thereby preparing a high-strength self-healing double-network hydrogel with excellent mechanical properties and self-healing properties.In order to achieve this goal,this paper has carried out the following work:(1)Design and synthesize the first layer network cross-linked by acylhydra zone bond:using the method of first polymerization and then cross-linking,firs t synthesize polymer gel factors containing hydrazide and ketone carbonyl funct ional groups at the side groups,and then condense to form acylhydrazone Bon d,prepare the acylhydrazone bond cross-linked hydrogel,and explore its self-hea ling performance and swelling stability.(2)A water-soluble crosslinking agent with dynamic covalent bonds was synthesized:using taurine,methyl acrylate and diacetone acrylamide as raw materials to synthesize polymerizable materials through Micheal addition,hydrazinolysis and condensation reactions The acyl hydrazone bond crosslinking agent;Vinyl imidazole,N-hydroxyphthalimide and diacetone acrylamide as raw materials to synthesize polymerizable oxime bond crosslinking agent.(3)Synthesis and performance study of dual network hydrogels crosslinked by dynamic covalent bond:A series of dual network hydrogels were prepared using oxime bond crosslinking agent,and the structure and performance of polymer networks and hydrogels C haracterized and optimized the preparation conditions of this type of double network hydrogel.Research indicates:(1)The polymer gel factor containing hydrazide and ketone carbonyl functional groups can obtain hydrogel cross-linked by acylhydrazone bond through condensation reaction,but the obtained hydrogel has weak strength,is unstable in water,and does not have swelling Stability,cannot be used as the first layer network to construct double network hydrogel.The possible reason is that the hydrazone bond formed by hydrazide and ketone carbonyl is not stable enough.(2)The condensation of diacetone acrylamide and carbohydrazide can obtain an acylhydrazone bond crosslinker,but the crosslinker is insoluble in water,which limits its application in synthetic hydrogels.The introduction of the sulfonate functional group by taurine can solve the water solubility problem of the acylhydrazone bond crosslinking agent.However,due to the reversible characteristics of the acylhydrazone bond,the stability of this crosslinking agent in water is not good,and it is neutral at room temperature.Under conditions,it is easy to partially decompose into raw materials.Using vinylimidazole and N-hydroxyphthalimide as raw materials,a water-soluble oxime bond crosslinking agent can be synthesized.This crosslinking agent is more stable than acylhydrazone bond crosslinking agents and can be used for dual network hydrogels.Synthesis.(3)The reversible crosslinking of oxime bonds can significa ntly improve t he tensile breaking strength and elongation of single-network hydrogels;the ten sile breaking strength and elongation of double-network hydrogels are far better than those of single-network hydrogels.The PAMPS-Na/PAAm double network hydrogel prepared by the oxime bond crosslinking agent has a breaking elong ation of 225.5%,a breaking strength of 1.83 MPa,and a toughness W of 1.55MJ/m~3;PDMAPAA-Q/PAAm double network water The elongation at break of the gel is 225.4%,the breaking strength is 1.4 MPa,and the strength and tou ghness W is 1.32 MJ/m~3.The PDMA/PAAm dual network hydrogel has weak properties,with a breaking elongation of 138.6%,a breaking strength of 0.182MPa,and a strength and toughness W of 0.11 MJ/m~3.The tensile properties of the double-network hydrogel prepared by ionic monomers are significantly bett er than those prepared by neutral monomers.The oxime bond cross-linked dou ble-n-etwork hydrogel has certain self-healing properties,and the double-networ k hyd-rogel can self-heal to a certain extent under a certain amount of acetic acid or 2,4-dimethoxyaniline.