LONG-TIME DYNAMICS IN POLY(DIMETHYLSILOXANE) NETWORKS STUDIED BY DEUTERIUM NUCLEAR-MAGNETIC-RESONANCE

A deuterium NMR (nuclear magnetic resonance) method is proposed to inv estigate long-time correlation of chain orientation in poly(dimethylsi loxane) networks. It is based on the observation of a quadrupolar echo after a Jeener pulse sequence, which is possible owing to the presenc e of nonzero residual interactions in the system related to local chai n orientations. The time evolution of the quadrupolar echo amplitude i s calculated in the framework of a slow chain reorientational motion. An experimental result is presented which shows that local orientation is frozen within the time scale investigated, up to 0.3 s.