CRITICAL RETENTION BEHAVIOR OF HOMOPOLYMERS

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.