  An unexpectedly large double spin correlation with a sharp dependence on
energy, found in elastic proton-proton scattering at large angles in the c.m.s.
energy range $\sqrt{s_{pp}}= 3 \div 5.5$ GeV, may be associated with the
formation of exotic eight-quark resonances at the thresholds of the strangeness
and charm production. For a deeper understanding of the dynamics of this
process it is important to measure double spin correlation in elastic $pn$
scattering in the same kinematics. The possibility of obtaining this data from
the reaction $d d\to pnp$ with two polarized deuterons on NICA SPD is
considered in this paper.
