We investigated the mechanism of the ring-opening copolymerization of ɛ-caprolactam (ɛ-CL) with glycidyl phenyl ether (GPE) to afford poly(ɛ-CL-co-GPE) as a model reaction of the thermal curing of certain epoxy resins with ɛ-CL. The reaction of ɛ-CL and GPE proceeded efficiently in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) at 170°C for 2 h. The monomer reactivities r1 of ɛ-CL and r2 of GPE calculated according to the Fineman-Ross method and the Kelen-Tüdös method were 0.58 and 5.52, respectively. These values indicate that poly(ɛ-CL-co-GPE) has a pseudo-block gradient copolymer. Based on these results, we examined the thermal curing reactions of certain epoxy resins with ɛ-CL. The corresponding novel cured products were obtained quantitatively, and each of them showed a high glass transition temperature and high thermal stability, presumably due at least in part to a pseudo-block gradient primary structure resembling that of poly(ɛ-CL-co-GPE)
