Mechanistic study of ring‐opening copolymerization of ɛ‐caprolactam with epoxide: Development of novel thermosetting epoxy resin system

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 r 1 of ɛ‐CL and r 2 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). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54 , 2220–2228