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General analytical expressions for Double Quantum Nuclear Magnetic Resonance(NMR) kinetic curves of many-spin I=1/2 systems are derived with an accuracy ofthe second cumulant approximation. The expressions obtained exactly describethe initial part of the kinetic curves and provide a reasonable approximationup to times of about twice the effective spin-relaxation time. For the casewhen the system contains two isolated spins, this result exactly reproducesknown expressions. In the case of polymer melts, the intermolecular magneticdipole-dipole interactions significantly influence the time dependence of theDQ NMR kinetic curves.

On the theory of Double Quantum NMR in polymer systems: the second cumulant approximation for many spin I=1/2 systems