Design And Synthesis Of Degradable Thermosetting Resins Containing Polyhexahydrotriazine Structure

Thermosetting resin matrix composites have been widely used in various fields,and the amount of waste has also increased dramatically.Thermosetting resins can not be reprocessed or reused because the permanent cross-linking structure will not change or break after the formation of cross-linking structure.Most of them are treated by incineration or landfill and cause serious environmental problems.In order to solve this problem,many studies on degradation and recovery of thermosetting resin matrix composites have been reported.Covalent adaptive network?CAN?is a new network containing reversible covalent chemical bonds,which is used for repairable,recyclable and processable thermosetting materials.In recent years,CAN has been widely used as an ideal method to recover or recycle advanced thermosetting resin matrix composites.Polyhexahydrotriazine?PHT?is also a new degradable CAN thermosetting resin.However,in the actual preparation process,we found that there is a huge contradiction between mechanical properties and degradation properties of CAN composites,so it is difficult to achieve the practical application of degradable thermosetting materials.In this paper,we use the optimized molecular structure design and curing process to control the crosslinking density and the formation degree of triazine structure in the crosslinking system,and prepare a new thermosetting resin with high mechanical,thermal properties and excellent degradation properties.The thermosetting resin is synthesized from polyformaldehyde?PFA?and diamine monomers sold in the market.The resin contains hemiaminal dynamic covalent network?HDCN?structure and PHT structure of cross-linking network.PHT structure makes thermosetting resins have high mechanical and thermal properties,and HDCN structure gives them rapid degradation.Two thermosetting PHT resins were prepared by two diamine monomers,3-bis?4'-aminophenoxy?benzene?TPE-R?and 1,4-bis?4-aminophenoxy?benzene?TPE-Q?.The two thermosetting resins have high tensile strength?TPE-R is 120MPa,TPE-Q is93MPa?and thermal stability(TPE-R T_d5%is 316?,TPE-Q T_d5%is 309?),and degradation performance?The degradation time of 0.05g TPE-R is 4.25h and that of TPE-Q is 4.67h?.Compared with TPE-Q-PHT resin,TPE-R-PHT resin has better mechanical properties,thermal stability and degradation performance.The combination of mechanical properties,thermal properties and degradation properties of the degradable thermosetting resin has never been realized in the existing reference data,and can solve the contradiction between the properties of the existing degradable thermosetting resin and realize the practical application of the degradable thermosetting material.Therefore,the new degradable thermosetting resins and their composites studied in this paper have great potential to be used as matrix materials in various applications.