Cooperative dynamics of macromolecules in polymer networks and spin-lattice relaxation

The Ngai model of cooperative dynamics is employed to describe the spin-lattice relaxation in a network polymer, A modified equation for the orientational correlation function of the vector connecting nuclei is proposed. The frequency and temperature dependences of the inverse spin-lattice relaxation time 1/T-1, are calculated. As the coupling parameter n (i.e,, the parameter characterizing the cooperativity of macromolecular dynamics) increases, the spectrum of relaxation times widens and its maximum shifts. The theory is compared with experimental data on the temperature dependence of 1/T-1 for fluorine nuclei in a cross-linked poly(heptafluorobutyl acrylate) with different content of the cross-linking agent.