  A general theory has been developed for a polydisperse semi-flexible
multi-block copolymer melt. Using the Bawendi-Freed approach to model
semi-flexible chains an expression for the Landau free energy is derived in the
weak segregation regime which includes the density and orientation
order-parameters. The orientation order-parameter is described in the smectic
phase and in more complicated structures such as the hexagonal phase. The
Landau free energy contains contributions of two kinds of interactions. The
first kind is the Flory- Huggins interaction which describes the
incompatibility of chemically different blocks and may induce microphase
separation. The second kind is the Maier- Saupe interaction which may induce
nematic ordening. In the framework of the weak segragation limit the Landau
theory allows to predict phase structures in the melt as a function of the
composition, persistence length and the strength of the Flory-Huggins and
Maier-Saupe interaction. The general theory is applied to a simple system of
monodisperse semi-flexible diblock copolymers. In several phase diagrams a
number of possible phase structures is predicted such as the bcc, hexagonal,
smectic-A, smectic-C and nematic phase. The infuence of the Maier-Saupe
interaction on the microphase structure is thoroughly discussed.
