ORIENTATIONAL ELASTIC DEFORMATIONS OF HIG H-TEMPERATURE AND REENTRANTPOLYMER NEMATICS IN THE MAGNETIC-FIELD

For the thermotropic mesogenic comb-shaped polymer having M = (16.9-91 .0) x 10(3), orientational elastic deformations in the magnetic field were studied using the Freedericksz effect, In the nematic and reentra nt nematic phases, the temperature dependences of orientational deform ations in the magnetic field and birefringence were examined in the en tire range of the existence of the LC phase. At the points of the N-S- A phase transition, the optical anisotropy Delta n and, correspondingl y, the orientational order parameter S experience no marked changes. E xamination of mechanical equilibrium characteristics does not reveal a ny difference in the behavior of high-temperature and reentrant nemati c polymer phases. The polymer fraction of the lowest molecular mass sh ows an anomalous temperature dependence of the bend elastic constant K -3, which may be explained by the development of nuclei of the smectic phase in the nematic phase, In the interval of the molecular masses s tudied, both optical anisotropy and equilibrium mechanical characteris tics are shown to be independent of molecular mass.