  A coarse-graining strategy for dilute and semi-dilute solutions of
interacting polymers, and of colloid polymer mixtures is briefly described.
Monomer degrees of freedom are traced out to derive an effective, state
dependent pair potential between the polymer centres of mass. The cross-over
between good and poor solvent conditions is discussed within a scaling
analysis. The method is extended to block copolymers represented as "necklaces"
of soft "blobs", and its success is illustrated here in the case of a symmetric
diblock copolymer which exhibits microphase separation.
