Abstract
The molecular dynamics of crosslinked polyurethanes have been studied by dielectric spectroscopy and compared with the dynamics of linear polyurethanes. Two local relaxations, gamma and beta, and a primary relaxation, alpha, were observed for all the samples, appearing in relation with the increase in temperature. The conductivity was studied at temperatures higher than the glass transition temperature and it was found to decrease with the increasing content of crosslinker. The presence of crosslinks strongly influences their dielectric properties, especially in the elastic state. The linear polyurethane exhibits the lowest alpha-relaxation temperature. For the crosslinked samples, alpha-relaxation temperature increases with increase in the amount of crosslinkers; beta- and gamma-relaxations are less affected by chemical crosslinking and their activation energies are in the ranges 40-55 and 34-37 kJ/mol, respectively. For the linear polyurethane, there is an exception in the case of the gamma-relaxation, which has a higher activation energy determined by its physical crosslinks. Conductivity analysis reveals a high mobility of charge carriers and low barriers for the transport of the charged particles. Also, the conductivity process is dependent on the segmental mobility of polymers.