  A generalized self-consistent field approach for polymer networks with fixed
topology is developed. It is shown that the theory reproduces the localization
of crosslinks which is characteristic for gels. The theory is then used to
study the order-disorder transition in regular networks of endlinked diblock
copolymers. Compared to diblock copolymer melts, the transition is shifted
towards lower values of the incompatibility parameter $\chi$ (the Flory-
Huggins parameter). Moreover, the transition becomes strongly first order
already at the mean-field level. If stress is applied, the transition is
further shifted and finally vanishes in a critical point.
