Organogelation behavior, thermal and mechanical properties of polymer network formed by the Diels–Alder reaction of furan- and maleimide-terminated four-arm star-shaped ε-caprolactone oligomers

Furan- and maleimide-terminated 4-arm star-shaped ε-caprolactone oligomers (F4CLO and M4CLO) were synthesized by the reactions of hydroxy-terminated 4-arm star-shaped ε-caprolactone oligomers (H4CLO) having the degree of polymerization per one oligocaprolactone chain, n = 5 or 10 with furfuryl isocyanate and 4-(maleimidophenyl)isocyanate, respectively. Solutions of F4CLO/M4CLO or F4CLO/4,4′-bismaleimidediphenylmethane (BMI) in some organic solvents changed to gels by the Diels–Alder (DA) reaction at 50 °C or room temperature, which came back to solutions by the retro-DA (rDA) reaction at 80 °C. The thermo-reversible sol–gel process due to the DA and rDA reactions was monitored by 1H NMR and GPC analyses. DSC and XRD analyses of polymer network formed by the DA reaction revealed that the network composed of the oligocaprolactone chain of n = 10 is semicrystalline, while that of n = 5 is amorphous. The former polymer network showed higher tensile strength and modulus than the latter.