Preparation And Properties Of Vitrimer Based On Terephthalaldehyde And Dynamic Imine Bond

In 2011,Leiber prepared the transesterification-based vitrimer material by adding a suitable transesterification catalyst to the polyester-based network of epoxy resin and fatty acid/polyacid.Vitrimer has excellent mechanical properties and can be reprocessed under certain stimulation like thermoplastic material,extending the life cycle of the material and reducing environmental pollution.It has become a popular research material in recent years.Since then,researchers have successively developed vitrimer materials based on disulfide exchange,silicone-silanol exchange,and olefin metathesis.Among them,based on the condensation of readily available monomeric amines and aldehydes readily available monomeric,the polyimine vitrimer material with dynamic imine bond can be remolded,processed and recycled without catalyst.It has attracted the attention of many scholars.In Chapter 2,polyimine material?PTI-mP?was prepared from p-phthalaldehyde,m-phenylenediamine and tris?2-aminoethyl?amine as raw materials.The influence of hot pressing temperature and hot pressing time on the mechanical properties of polyimine material were investigating.The PTI-mP was prepared under the optimal condition of hot pressing temperature of 105°C and hot pressing time of 1 h.On this basis,the other three polyimide vitrimer materials,named PTI-H and PTI-CH and PTI-pP respectively,were prepared by the same method using hexamethylenediamine,1,4-diaminocyclohexane,and p-phenylenediamine as raw materials,and their structures were characterized by Fourier transform infrared spectroscopy.The effects of the diamine structure on the physical and mechanical properties of polyimine vitrimer materials were studied by tensile test,dynamic mechanical analysis and the thermal analysis.The results show that PTI-CH and PTI-mP with rigid cyclic hydrocarbon structure and higher cross-link density exhibit high tensile strength?>55 MPa?,storage modulus?>1.8 GPa?and low elongation?<36%?.PTI-H with a flexible fatty chain structure and lower crosslink density shows weaker tensile strength?30.9 MPa?,storage modulus?1.68 GPa?and better elongation?51.2%?.The four polyimine materials can be remolded in a short time at a relatively low temperature?120°C?.In Chapter 3,a series of polyimine vitrimer materials with specific ratios were prepared using terephthalaldehyde,macromolecule polyethyleneimine?PEI?and decanediamine of biomass derivative as raw materials.The effect of monomer ratio on the physical and mechanical properties of polyimine materials was explored by the hydrophilic test and tensile test,finding that the hydrophilicity of the material increased and the mechanical properties gradually decreased with the increase of PEI content.At the molar ratio of diamine:terephthalaldehyde:polyethyleneimine of 0.3:1:0.47,the polyimine vitrimer--PTI-PEI₇₀-X?X represents the diamine type?were prepared by the schiff base reaction of p-phthalaldehyde and tris?2-aminoethyl?amine with 1,4-diaminocyclohexane,hexamethylenediamine,and decanediamine respectively.Fourier transform infrared spectroscopy and solubility tests showed that PTI-PEI₇₀-X has formed a three-dimensional network with imine bonds structure.The tensile test and thermal analysis test show that PTI-PEI₇₀-CH has a relatively high T_g and tensile strength due to the rigid structure of the polyimine material.Howerer,the elongation at break is low.PTI-PEI₇₀-DM with a long flexible carbon chain shows a low Tg and tensile strength?5.83 MPa?and higher elongation at break?117%?.The three polyimine materials can be remodeled at a temperature of 110°C,and the mechanical properties after reshaping are comparable to the original samples.