The critical concentration c** which separates the regime of extremely dilu
te solutions from that of dilute solutions of polymers was studied in the s
tatic state and in flowing solution. This concentration is lower when deter
mined by UV measurements in the static state compared to the critical conce
ntration determined in the dynamic state using viscosimetry. The influence
of the molecular mass of the polymer and of the temperature on the critical
concentration was studied. Further arguments are presented which can be ma
de in favor of the assumption that in the critical concentration c** entang
lements emerge between the macromolecular chains.