Synthesis And Properties Of Self-repairing Cross-linked Polyamides Based On Diels-alder Reaction

Diels-Alder(DA)reaction is particularly suitable for preparing thermally stimulated self-healing polymers because of its excellent thermal reversibility,high yield,few side reactions and mild reaction conditions.DA reaction has been widely used in polyesters,epoxy resins and polyurethanes,but is still rarely used in cross-linked polyamides.Cross-linked polyamides are also important polymer materials with excellent resistance to organic solvents and high mechanical strength.They can be used in coatings,adhesives,composites,separation membranes,etc.Meanwhile,damage during use usually cause their performance decline and shorten their service life.In this paper,bulk Michael addition,polycondensation,and DA reaction were used to synthesize cross-linked polyamides with reversible DA bonds suitable to thermal self-repairing.The specific research contents are described as follows:1.A furfurylamine diester(Fu-MADE)was synthesized through a Michael addition of methyl acrylate and furfurylamine.Bulk polycondensation of Fu-MADE with polyether diamine(D230)and polyether triamine(T440)was conducted at the ester/amine molar ratio of 4:3,and several branched polyamide prepolymers(pFU-PA-x%s)(x,the T440 content in feed)with furan pendent groups and ester groups end-capped were prepared.The pFU-PA-x%s were reacted further with 1,5-bismaleimido-2-methylpentane(BMIMP),and self-repairing cross-linked polyamides(PA-FU-DA-x%s)were obtained.The effect of T440 content on the performance was discussed.The results show that as the content of T440 increases,the Tg and tensile strength all increase.Among them,PA-FU-DA-20%has the largest tensile strength reaching 17.51 MPa,and the self-healing efficiency is around 70%.2.In order to improve the performance,the materials in this chapter were synthesized differently.The T440 used in the previous chapter was replaced by a diamine with benzene ring(m-xylylenediamine,MXDA),and the reaction temperature was increased to 190?.Melt polycondensation of FU-MADE,D230 and MXDA was carried out at the ester/amine molar ratio of 4:3 and 6:5,respectively,and linear polyamide prepolymers with pendent groups and ester groups end-capped(n is the total mole of diamines,and x is the MXDA content in feed)(pFU-PA-nx%s)were prepared.The pFU-PA-nx%s were then reacted with BMIMP,and final products DA self-repairing cross-linked polyamides(PA-FU-DA-n-x%s)were obtained.The influence of MXDA content and ester/amine molar ratio on the products was discussed.The results show that as the MXDA content and ester/amine molar ratio increase,the Tg and tensile strength all increase,while the dissolution rate decreases accordingly.When the ester/amine molar ratio was at 6:5,the dissolution rate was reduced to 3.35%,and the tensile strength was the highest,up to 36.54 MPa.After repairing at 130? for 1.5 h,the self-healing efficiency is as high as 70%or more.PA-FU-DA-5-0%has the highest self-healing efficiency up to 92.66%with the tensile strength after repair of 11.36 MPa.3.Similarly to the previous chapters,two flexible linear polyamide prepolymers with furan pendent groups(m is 230 or 440)(pFU-Dm-PAs)were first prepared by reacting FU-MADE with polyether diamine D400 or D230.Meanwhile,a piperazine tetraester(PTFU)was synthesized through a bulk Michael addition of anhydrous piperazine and dimethyl maleate,and was polycondensed with furan methylamine to obtain a furan groups end-capped and rigid star polyamide prepolymer(pFU-PTFU-PA).Finally,the pFU-Dm-PAs and pFU-PTFU-PA were reacted with BMIMP,and DA self-healing cross-linked polyamides(cPA-DA-Dm-x%s)(PTFU)were obtained.The influence of the rigid PTFU content and the flexible Dm length on final products was discussed.The results show that with the increase of PTFU content,both Tg and tensile strength increase.Compared with cPA-DA-D400-x%series,the comprehensive mechanical properties of cPA-DA-D230-x%series are better.The self-healing efficiency of them is higher than 87%.The initial tensile strength of cPA-DA-D230-30%is the largest,up to 30.05 MPa.