  Polymers in nonuniform flows undergo strong deformation, which in the
presence of persistent stretching can result in the coil-stretch transition.
This phenomenon has been characterized by using the formalism of nonequilibrium
statistical mechanics. In particular, the entropy of the polymer extension
reaches a maximum at the transition. We extend the entropic characterization of
the coil-stretch transition by studying the differential entropy of the polymer
fractional extension in a set of laminar and random velocity fields that are
benchmarks for the study of polymer stretching in flow. In the case of random
velocity fields, a suitable description of the transition is obtained by
considering the entropy of the logarithm of the extension instead of the
entropy of the extension itself. Entropy emerges as an effective tool for
capturing the coil-stretch transition and comparing its features in different
flows.
