Effect of Pressure\non the Micellar Structure of PMMA‑<i>b</i>‑PNIPAM\nDiblock Copolymers in Aqueous Solution

The phase behavior\nas well as the pressure- and temperature-dependence\nof the micellar structure of the thermoresponsive amphiphilic diblock\ncopolymer PMMA<sub>21</sub>-<i>b</i>-PNIPAM<sub>283</sub> in D<sub>2</sub>O are investigated. The coexistence line of PMMA<sub>21</sub>-<i>b</i>-PNIPAM<sub>283</sub> in D<sub>2</sub>O in the temperature–pressure frame is shifted to lower in\ntemperature and pressure compared to PNIPAM homopolymers in D<sub>2</sub>O. High-pressure small-angle neutron scattering (SANS) provides\ninsights into the structure and aggregation behavior of the micelles\nboth in the one-phase and the two-phase regions. In the one-phase\nregion, pressure does not noticeably alter the core–shell structure\nof the micelles. Upon heating the solution at atmospheric pressure\ninto the two-phase region, the micellar shell strongly dehydrates\nand shrinks. Conversely, the micellar shell remains hydrated when\nthe coexistence line is crossed either by heating at 35 and 75 MPa,\nor by increasing the pressure at 31.8 °C. Moreover, along both\npathways, the aggregates in the two-phase region are significantly\nlarger than at atmospheric pressure.