Synthesis of PDMS-b-POEGMA Diblock Copolymers and Their Application for the Thermoresponsive Stabilization of Water-Supercritical Carbon Dioxide Emulsions

In this study, PDMS13-b-POEGMA(x) diblock copolymers consisting of a CO2-philic poly(dimethylsiloxane) (PDMS) block connected to a thermosensitive hydrophilic poly(oligoethylene glycol methacrylate) (POEGMA) block were synthesized by reversible addition-fragmentation chain-transfer (RAFT) radical polymerization. Their ability to decrease the water-supercritical CO2 (scCO(2)) interfacial tension (gamma) and to stabilize water-scCO(2) emulsions was investigated using an original homemade device developed in the laboratory. This device is able to control the pressure from 1 to 250 bar and the temperature from 40 to 80 degrees C. It was implemented with 2 visualization windows, a drop tensiometer and a remote optical head for dynamic light scattering (DLS) measurements. These experiments revealed that PDMS-b-POEGMA decreased gamma down to 1-2 mN/m and was the most efficient at high pressure (250 bar) and low temperature (40 degrees C) where PDMS and POEGMA blocks exhibited the highest affinity for their respective phase. The diblock copolymers were shown to stabilize water-scCO(2) emulsions. Moreover, the thermosensitive behavior of the POEGMA block in water (with a lower critical solubility temperature around 65 degrees C) resulted in the formation of temperature-responsive emulsions that could reversibly switch at 100 bar from stable at 40 degrees C to unstable at 80 degrees C. These results were rationalized based on the solubility of each individual block of the copolymers in water and scCO(2) as a function of temperature and pressure.