Preparation And Properties Of Recyclable And Degradable Materials Based On Bio-based Diacetal Vitrimer

Compared with thermoplastic polymers,thermosetting polymers usually have higher strength and modulus,and show higher chemical resistance and dimensional stability because of their cross-linked network structure.Because of these properties,thermosetting polymers are widely used in many fields.However,under the background of carbon neutralization,the recycling of thermosetting polymers has attracted more and more attention.This is because once a cross-linked network is formed,thermosetting polymers become infusible and insoluble,making them difficult to repair and recover.As a new material,Vitrimer has excellent mechanical properties,solvent resistance,and thermodynamic properties,as well as remodeling,self-healing,weldability,reprocessing and recycling,so it is a very promising material.However,at present,the starting materials of most Vitrimer materials are petrochemical raw materials.Although the products come from a wide range of sources,they do not have sustainable development.In the case of increasing depletion of petroleum resources and rising prices,it is of great significance to use renewable resources as raw materials to develop new Vitrimer materials.In this thesis,to solve the problems of recyclability,renewability and degradability of traditional thermosetting materials,we introduced a new type of bio-based spirocyclic diacetal dynamic covalent bond into the polymer skeleton to prepare a series of recyclable and biodegradable Vitrimer materials and explored their closed-loop recyclability and application potential as adsorption materials.The details are as follows:(1)The three novel fully biobased acetal monomers(SAE,VE,EVE)were synthesized from three different biobased phenol materials(vanillin,ethyl vanillin and eugenol)and erythritol,and cured with biobased epoxidized soybean oil to obtain three new fully biobased Vitrimer materials(SAE-E,VE-E,EVE-E).The spatial site resistance of the acetal monomer structure was found to influence the mechanical strength(SAE:15 MPa;VE:13 MPa;EVE:8.3 MPa),glass transition temperatures(SAE-E,59°C;VE-E,51°C;EVE-E,41°C)and activation energy of the exchange reaction(SAE:82.97 k J/mol;VE:58.45 k J/mol;EVE:69.84 k J/mol).The acetal structure embedded in the cross-linked network also gives the three materials good recyclability(90%retention of mechanical properties after three remouldings)and thermal stability(<10%weight loss at 300°C).In addition,the closed-loop recyclability of the materials was investigated,and it was found that the recycled materials retained approximately 80%of their mechanical properties.This research work will provide a new avenue for the preparation of recyclable and degradable Vitrimer materials from fully biobased green materials and will further promote the application of biobased Vitrimer materials.(2)Bio-based diacetal phenol monomers(VPV)were prepared from bio-based vanillin and pentaerythritol,and Vitrimer materials containing degradable acetal structures(VPV-TH)were prepared by phenol-yne"click"polymerization,and Vitrimer materials containing bisphenol A structures(BPA-TH)were prepared by the same cross-linking method.Small molecule modelling experiments were first carried out to find the dynamic nature of the enol-one bonds resulting from the phenol-yne"click"reaction,and the activation energy(E_a)required for the enol-one bond exchange was found to be 77±3 k J/mol.The tensile properties of the two materials(VPV-TH and BPA-TH)were then investigated(VPV-TH:36 MPa;BPA-TH:36 MPa;BPA-TH:29MPa),thermal stability properties(95 wt%retention at 320°C)and recyclability(95%retention of mechanical properties after three remouldings)were then investigated.Due to the structural differences between the two polymer networks,VPV-TH is susceptible to degradation,while BPA-TH exhibits acid resistance stability.Finally,porous polymer films with a porosity of 46%were prepared by solid phase fusion and selective degradation of the two materials(VPV-TH and BPA-TH).The films have an oil absorption rate of 46%and can be recycled many times over.This research work is the first application of Vitrimer materials to porous polymer materials and provides a new avenue for the application of Vitrimer materials.