Dynamic mechanical thermal analysis of thermally stable and thermally reactive network polymers

The temperature and frequency dependence of the dynamic mechanical properties in the glass transition was studied for a series of partially cured thermally reactive networks (low temperature cured epoxy and a dimethacrylate photocured with a conventional initiator) and more thermally stable networks (high temperature cured epoxy and two dimethacrylates photocured with a photoiniterl). The viscoelastic behavior in the transition region of the former networks changed during the experiment due to additional cure, whereas the thermally stable networks enabled the study of the effect of conversion on the transition region. The glass transition temperatures showed 1 : 1 relationships with the isothermal curing temperatures and were correlated with the degree of conversion. The breadth of the glass transition, as determined from the real and loss moduli, tan delta, and the loss compliance in the temperature and frequency domains, was found to be greater for the dimethacrylate networks than for the epoxy networks. The breadth of the transition for the dimethacrylates was not significantly dependent on the degree of cure. (C) 2004 Wiley Periodicals, Inc.