Catalyzed Michael addition, polycondensation, and the related performance of Diels–Alder self-healing crosslinked polyamides

Diels–Alder (DA) addition is an efficient method to repair damages at mild conditions. It is often used in self-healing polyurethanes and epoxy resins and seldom used in cross-linked polyamides (cPAs). Michael addition becomes a useful method to synthesize cPAs. However, no efficient way has been established to conduct double-addition of primary amines. In this work, organic catalyzed Michael addition and polycondensation were established to prepare polyamide oligomers with furan pendent groups (pFU-PAs), and a DA addition was adopted to prepare self-healing cross-linked polyamides (SH-cPAs). A bulk double Michael addition of furfurylamine and methyl acrylate was performed at 30–70°C in the presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), or 4-(N,N-dimethylamino) pyridine (DMAP), and a high yield of furfurylamine-N,N-bis(methyl propionate) (FA-BMP) was prepared. The catalytic activity order is MTBD>TBD >>DMAP in Michael addition. Melt polycondensation of FA-BMP with bis(2-aminopropyl) polypropyleneglycol and hexamethylene diamine was catalyzed by MTBD and N,N′-diphenylthiourea. The DA addition of 1,5-bismaleimido-2-methylpentane and pFU-PAs was monitored by FT-IR, 1 H NMR, DSC, polarizing optical microscopy, and gel content. In these catalyzed processes, the structures of FA-BMP, pFU-PAs, and SH-cPAs were controlled easily, and the SH-cPAs showed good mechanical property and excellent self-healing performance of 88%–98%.