Nuclear magnetic relaxation, correlation time spectrum, and molecular dynamics in a linear polymer

The pulsed nuclear magnetic resonance (NMR) method at a proton frequency of 25 MHz at temperatures of 22-160 degrees C is used to detect the transverse magnetization decay in polyisoprene rubbers with various molecular masses, to determine the NMR damping time T-2, and to measure spin-lattice relaxation time T-1 and time T-2eff of damping of solid-echo signals under the action of a sequence of MW-4 pulses modified by introducing 180 degrees pulses. The dispersion dependences of T-2eff obtained for each temperature are combined into one using the temperature-frequency equivalence principle. On the basis of the combined dispersion dependence of T-2eff and the data on T-2 and T-1, the correlation time spectrum of molecular movements is constructed. Analysis of the shape of this spectrum shows that the dynamics of polymer molecules can be described in the first approximation by the Doi-Edwards tube-reptation model.