  Based on a recently established formalism (U. Ebert, J. Stat. Phys. 82, 183
(1996)) we analyze the diffusive motion of a long polymer in a quenched random
medium. The medium is modeled by a frozen semidilute polymer system. In the
framework of standard renormalization group (RG) theory we present a systematic
perturbative approach to handle such a many chain system. In contrast to the
work of Ebert we here deal with long range correlated disorder and find an
attractive RG fixed point. Unlike in polymer statics the semidilute limit here
yields new nontrivial power laws for dynamic quantities. The exponents are
intermediate between the Rouse and reptation results. An explicit one loop
calculation for the center of mass motion is given.
