Preparation And Properties Of Bio-based Degradable Thermostting Resins Based On Thiol-ene Clink Reaction

Thermosetting resins are widely used in various fields due to their excellent comprehensive properties and play an irreplaceable role in many applications.However,due to the insoluble and immiscible permanent cross-linked network structure of thermosetting resins and their inability to be repeatedly processed and molded during the polymerization process,it is difficult to degrade and recover them after their service life,which can easily lead to resource waste and environmental pollution issues.At the same time,the synthesis of traditional thermosetting resins is heavily dependent on the constantly depleted petrochemical resources,making the greening of the polymer industry increasingly important.The bio-based materials is receiving increasing attention.However,it is difficult for bio-based degradable resins to have good mechanical and thermal properties.Therefore,in this paper,two high-performance bio-based degradable thermosetting resins based on thiol-ene click reaction were synthesized from two aspects:degradable design and the use of bio-based materials.The main research contents and results are as follows:（1）In this section,,degradable,hydrolysable and high mechanical property eugenol-based thiol-ene click crosslinking network was designed and prepared.Using eugenol as raw material,three kinds of fully bio-based diallyl monomers EUSC,EUAC,and EUSD with different flexible segment lengths were designed and synthesized by reacting with succinyl chloride,adipoyl chloride and sebacoyl dichloride,respectively.The molecular structures of the three monomers were characterized by FTIR,¹H NMR,and ¹³C NMR.Then,three kinds of eugenol-based diallyl monomers and pentaerythritol tetra（3-mercaptopropionate）（PETMP）had a thiol-ene click reaction to form three kinds of eugenol-based thiol-ene cross-linked networks SC/T,AC/T,and SD/T.The effects of flexible segment length on the thermal properties,thermos-mechanical properties,thermal stability,mechanical properties and degradation properties of cross-linked networks were studied.As the length of the flexible chain segment increases,the glass transition temperature T_{g DMA}and T_{g DSC}gradually decrease.Among them,SC/T exhibits the highest glass transition temperature and mechanical properties,that T_{g DMA} is 32.8℃,tensile strength is40.51 MPa and Young’s modulus is 1.67 GPa.In addition,the ester bonds introduced in the three types of fully bio-based networks give them degradability.The solidified films are completely degraded in an alkaline aqueous solution at 90℃,which provides reference significance for the structural design of bio-based degradable high-performance thermosetting resins.（2）In this section,a hydrolysable,high-performance and closed-loop monomer recyclable resveratrol-based thiol-ene click crosslinking network was designed and prepared.A bio-based allyl monomer（RAC）with a carbonate bond was designed and synthesized by using resveratrol as bio-based raw material and reacting with allyl chloroformate.The molecular structure of RAC was determined by FTIR,¹H NMR,¹³C NMR and MS characterization.Three thermosetting cross-linked networks were formed through the thiol-ene click reaction of RAC with three different functional mercaptans.The thermal properties,thermos-mechanical properties,thermal stability,mechanical properties and degradation recovery properties of resveratrol-based thermosetting networks were studied.Among them,RAC/T4 with the highest crosslinking density exhibits the best comprehensive properties,with T_{g DMA}of76.1℃,tensile strength of 49.4 MPa and Young’s modulus of 1.2 GPa.Adjustable comprehensive performance can be achieved by controlling the functionality of sulfhydryl groups.In addition,the carbonate and ester bonds in the RAC/T networks give them good degradability.After complete degradation in 1 M alkaline solution,the original bio-based raw material monomer resveratrol can be recovered from the degradation product,achieving closed-loop monomer recovery of biomass.This provides reference significance for the structural design of high-performance bio-based degradable and recyclable thermosetting resins based and a new idea for solving the non-melting and non-dissolving problem of traditional thermosetting resins.And this also contributes to the sustainable development of biomass materials.