Phase Behaviours of Polybutadiene–Polyacrylic Acid Brushes in Compressed Carbon Dioxide

Our present work investigated the phase behaviour of polybutadiene–poly acrylic acid (PB–PAA) brushes–solvent–CO2 ternary system in detail. The phase separation pressures increased with increasing temperatures and solid contents of PB–PAA solution, and decreased with increasing sizes of the brushes. Considering that the expansion of water was much smaller than that of ethanol by compressed CO2, a higher cloud point pressure of CO2 could be employed to reach the phase separation when water was added as the co-solvent. Owing to the penetration of CO2 into the periphery of the shell, the chains of the polymer brushes initially shrank and then turned to aggregations before finally precipitating upon CO2 addition. Our results provide a simple and effective way for separation and recovery of polymer brushes that could promote a wider range of their applications.