| Diels-Alder(DA)self-healing polymers have become an important material of which the mechanical strength of damaged samples can be restored in whole or part at certain stimuli.At present,the most investigated DA self-healing polymers include self-healing epoxy resins,polyurethanes,and polymethacrylates,but seldom contain self-healing polyamides.Crosslinked polyamides(cPAs)usually show excellent mechanical properties,low insolubility,poor infusibility,and difficult recycling.Introducing DA bonds may make the reprocessing of cPAs easy.In this paper,a series of self-healing cross-linked polyamides were synthesized through an organic catalyzed Michael addition,melt polycondensation,and DA addition.They show excellent mechanical property and good self-healing performance.The contents are described in detain as follows:1.Michael addition becomes an important method in organic and polymer synthesis because of its mild reaction condition,favorable reaction rate,high conversion,and atomic economy.In the aza-Michael addition of primary amines with methyl acrylate(MA),the mono-addition of the first N-H bond in H2N-group with MA takes place easity,but the double-addition of the second N-H bond is extremely difficult.At present,there has been no efficient way to make all primary N-Hs react completely.In this section,the Michael addition of primary mono-and multi-amines with MA was catalyzed by different organic tertiary amines,i.e.1,5,7triazabicyclo[4.4.0]dec-5-ene(TBD),7-methyl-TBD(MTBD),and N,Ndimethylamino pyridine(DMAP),at 30-70℃.We found that DMAP shows low catalytic activity,while TBD and MTBD are highly active.With MTBD as the catalyst,N,N-bis(methyl propanate)furfurylamine(FA-DE),N,N-bis(methyl propanate)butylamine,N,N,N’-tris(methyl propanate)aminoethylpiperazine,N,N,N’,N’-tetra(methyl propanate)hexamethylene diamine were synthesized efficiently from the Michael addition of furfurylamine(FA),1-butylamine(BA),N-aminoethylpiperazine(AEPZ),and hexanediamine(HDA)with MA.The MA conversion and doubleaddition yield are both above 90%.An effective,simple,and gentle synthesis strategy for double Michael addition of primary H2N-with MA was established.2.In our previous work,we found that melt polycondensation of diamines and diesters usually conducted very slowly without catalysts or in the presence of SnCl2 or ZnCl2,and the reaction extent was less than 80%.Many terminal H2N-groups were left in the obtained PA prepolymers,which easily caused irreversible crosslinked bonds in final self-sealing PAs.In this section,the bult polycondensation of FA-DE and diamines(D230,hexamethylene diamine)was conducted at the synergy catalysis of thiourea and MTBD.The catalyzed polycondensation greatly increased reaction extent,and the terminal H2N-groups were efficiently reduced.The linear PA prepolymers with furan side groups were prepared,and were cured with a bismaleimide to obtain self-sealing cross-linked polyamides.They exhibit tensile strength up to 26.04 MPa,low elongation at break of 5.59%,and multiple high-efficiency self-healing.Their performance was regulated by adjusting the D230/hexamethylene diamine molar ratio in the PA prepolymers.3.Several ester-terminated PA prepolymers were prepared through bulk polycondensation of dimer acid and excessive hexamethylene diamine.Further polycondensation of the PA prepolymers with excess FADE were conducted at the synergy catalysis of thiourea and MTBD,and a series of PA prepolymers with furan side groups were obtained.After mixing them with a bismaleimide,the self-sealing cross-linked polyamides were prepared.They were characterized by FT-IR,DSC,1H NMR and tensile test.The self-sealing polyamides exhibited tensile strength up to 16.94 MPa and excellent toughness with the elongation at break of 169.28%.They showed good self-healing ability.The crack can be repaired in 5 minutes at 140℃. |
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