Ultrasensitive Differential Scanning Calorimetric (US-DSC) Study of the Thermal-Induced Dynamic Transition Behaviors of PEO-PPO-PEO in Aqueous Solution.

Temperature-responsive macromolecules can provide insights into the mechanisms of the aggregation and precipitation processes of proteins. In this study, the PEO-PPO-PEO triblock copolymer, Pluronic P123, has been utilized as a protein model to investigate the thermally induced dynamic transition behavior by ultrasensitive differential scanning calorimetry (US-DSC). The results of US-DSC reveal hysteresis in the disaggregation process of P123 micelles. Combined with the particle size distribution, a stepwise disaggregation mechanism is proposed. The disaggregation of P123 micelles in the cooling process involved rod-to-sphere transition, fragmentation, and dissolution of micelles. Moreover, US-DSC results show that both the sphere-to-rod transition and micelle fragmentation are dependent on the scanning rate and reveal the relationship between the dynamic transition and thermodynamic properties of P123. These findings expand the understanding not only of aggregation and disaggregation of P123 in dilute aqueous systems but also of the thermal unfolding and aggregation of proteins.