The isocratic retention behaviour of a homopolymer at a specific tempe
rature and varying solvent compositions can be divided into three mode
s: exclusion mode, transition mode (critical conditions) and adsorptio
n mode. Under critical conditions (a specific non-solvent/solvent comp
osition at a specific temperature) the retention of a homopolymer is i
ndependent of the molar mass. The critical conditions depend upon the
temperature, the type of polymer and the type of non-solvent/solvent m
ixture. A difference in the critical conditions between polystyrene st
andards and polybutadiene standards was found. No significant influenc
e of different types of column packing on the critical solvent composi
tion was noticed. The exact mechanism of the retention of a polymer un
der critical condition is not clear yet. In order to determine the cri
tical conditions, a new method has been developed. The method can be e
asily performed on existing equipment. The method contains a different
setup of the data acquired by isocratic HPLC than methods described i
n literature. Therefore, less experiments need to be performed to dete
rmine the critical conditions compared to the current method. The newl
y developed method is more efficient than the methods described in the
literature.