| Abstract: | Structure and properties of films obtained by the electron beam (EB) and the ultraviolet light (UV) solid-state polymerization of polyurethane–acrylate prepolymer were examined to reveal the characteristics of these radiation polymerizations. The prepolymer was synthesized by the reaction of poly(butylene adipate)diol, 4,4′-diphenylmethane diisocyanate, and 2-hydroxyethyl acrylate. EB polymerization behaviors of the prepolymer produced a unique polymer film different from that obtained by UV irradiation. Although polyurethane–acrylate films from the EB and the UV solid-state polymerizations consisted mainly of amorphous and crystalline phases, it was proved that the film from 10 Mrad of EB irradiation at 25°C had higher crystallinity and larger crystallite size than the film from UV irradiation. This is assumed to be due to the reason that EB irradiation below the melting point of the polyurethane–acrylate can lead to crosslinking without the destruction of the original crystalline structure. On the other hand, the UV polymerization proceeded with the melting of the crystalline structure by absorbing other lights than the UV absorbed by a photoinitiator. The EB-polymerized film which was crosslinked more densely than the UV-polymerized film showed higher mechanical strength than the latter film. |
