  We model a melt of monodisperse side-chain liquid crystalline polymers as a
melt of comb copolymers in which the side groups are rod-coil diblock
copolymers. We consider both excluded volume and Maier-Saupe interactions. The
first acts among any pair of segments while the latter acts only between rods.
Using a free energy functional calculated from this microscopic model, we study
the spinodal stability of the isotropic phase against density and orientational
fluctuations. The phase diagram obtained in this way predicts nematic and
smectic instabilities as well as the existence of microphases or phases with
modulated wave vector but without nematic ordering. Such microphases are the
result of the competition between the incompatibility among the blocks and the
connectivity constrains imposed by the spacer and the backbone. Also the
effects of the polymerization degree and structural conformation of the
monomeric units on the phase behavior of the side-chain liquid crystalline
polymers are studied.
