Gelation behavior and thermal and mechanical properties of polymer network formed by the Diels-Alder reaction of furan- and maleimide-terminated four-arm star-shaped ethylene glycol oligomers

Abstract

Furan-terminated four-arm star-shaped ethylene glycol oligomer (F4EGOn) was synthesized by the esterification reaction of furfuryl alcohol and succinate-terminated four-arm star-shaped ethylene glycol oligomer (S4EGOn) which was prepared by the reaction of succinic anhydride and hydroxy-terminated four-arm star-shaped ethylene glycol oligomer (H4EGOn) having the approximate degree of polymerization per one oligo(ethylene glycol) chain, n = 4 or 11. Also, maleimide-terminated four-arm star-shaped ethylene glycol oligomer (M4EGOn) was synthesized by the reaction of H4EGOn and 4-(maleimidophenyl)isocyanate. Solutions of F4EGO4/M4EGO4 and F4EGO11/M4EGO11 in 1,4-dioxane (DOX) or N,N-dimethylformamide (DMF) displayed thermo-reversible sol-gel transitions by the repeated Diels-Alder (DA) reactions at room temperature and retro DA reaction at 80 °C. Although F4EGO4/M4EGO4 was insoluble in water-containing solvents, F4EGO11/M4EGO11 was soluble in DMF/water or DOX/water 1/1, and the solution showed a sol-gel transition but only once or twice. Fourier transform infrared (FT-IR) analysis revealed that the conversion of DA reaction for the F4EGOn/M4EGOn (n = 4 or 11) film dried at 50 °C (F4EGOn-M4EGOn) was 87 % (n = 4) or 90 % (n = 11). The glass transition temperature and tensile strength of F4EGO4-M4EGO4 were higher than those of F4EGO11-M4EGO11. Both F4EGO4-M4EGO4 and F4EGO11-M4EGO11 were swellable to water, DOX/water 1/1, or DMF/water 1/1.