A distinction must be made between two different length scales. One regime will be given by small end to end vector scales R 0 < ξ ξ . At these scales the chain piece experiences only correlations from itself, i.e., the classical self-avoiding behavior. For larger scales R 0 > ξ ξ self-avoiding correlations do not play a significant role and the chain statistics resemble a Gaussian chain. The critical value ξ ξ must be a function of the concentration. Intuitively, one significant concentration can already be found. This concentration characterizes the overlap between the chains. If the polymers just marginally overlap, one chain is occupied in its own volume. This gives: