CRITICAL RETENTION BEHAVIOR OF HOMOPOLYMERS

The isocratic retention behaviour of a homopolymer at a specific temperature and varying solvent compositions can be divided into three modes: exclusion mode, transition mode (critical conditions) and adsorption mode. Under critical conditions (a specific non-solvent/solvent composition at a specific temperature) the retention of a homopolymer is independent of the molar mass. The critical conditions depend upon the temperature, the type of polymer and the type of non-solvent/solvent mixture. A difference in the critical conditions between polystyrene standards and polybutadiene standards was found. No significant influence of different types of column packing on the critical solvent composition was noticed. The exact mechanism of the retention of a polymer under critical condition is not clear yet. In order to determine the critical conditions, a new method has been developed. The method can be easily performed on existing equipment. The method contains a different setup of the data acquired by isocratic HPLC than methods described in literature. Therefore, less experiments need to be performed to determine the critical conditions compared to the current method. The newly developed method is more efficient than the methods described in the literature.