Molecular motions and the glass transition temperature (T g) of electron beam (EB) cured cycloaliphatic epoxy resins were found to be significantly different from those of ultraviolet (u.v.) cured resins by using high-resolution solid-state nuclear magnetic resonance and dynamic mechanical measurements. The resins used were polymerized with an aromatic sulphonium salt initiator. Dependence of initiator concentration on spin-lattice relaxation time in the rotating frame revealed that the initiator fragments remaining in the EB cured samples act as antiplasticizer and plasticizer below and above 3 wt% initiator concentration, respectively. The dependence in the u.v. cured samples is also similar, but the critical initiator concentration is 1 wt%. This finding means that the unexpected effect, namely antiplasticization, is less in the EB cured samples than in the u.v. cured samples at the initiator concentration in commercially available samples (~lwt%). In addition, the EB cured samples exhibit smaller Tg depression due to the antiplasticization-plasticization effect than the u.v. cured samples. Both the higher critical initiator concentration and the smaller Tg depression for the EB cured samples than for the u.v. cured samples are attributed to the lower concentration of the fragments remaining in the EB cured samples confirmed by their cross-polarization/magic angle spinning spectra.
Посилання на статтю:
Plasticization and antiplasticization effects of sulphonium salt initiator fragments remaining in cycloaliphatic epoxy resins cured by electron beam and ultraviolet irradiation / Atsushi Udagawa, Yasuhiko Yamamoto, Yoshio Inoue andRiichir8 Chujo // Polymer. – 1992. – Vol 33. – P. 264-267.