Well-defined surgar-containing amphiphiles and their application to the heterogeneous polymerization of water-soluble monomers in supercritical carbon dioxide

Supercritical carbon dioxide (scCO₂) is the most widely preferred supercritical fluid (SCF) because of its environmental acceptability and its easily accessible supercritical parameters. One major limitation to the broader use of scCO₂ is its inability to dissolve a wide range of highly polar compounds. This problem can be alleviated by the addition of CO ₂-philic amphiphiles. The primary objective is to design and synthesize well-defined polymeric surfactants that have both strong polar moieties and highly CO₂-philic segments. Novel amphiphilic diblock copolymers with well-defined glycopolymer blocks (poly(3-O-methacryloyl-1,2:5,6-di- O-isopropylidene-D-glucofuranose), PMAIpGlc) and fluoropolymer blocks (poly(1,1-dihydroperfluorooctyl methacrylate), PFOMA) were synthesized by living anionic polymerization. The resulting polymers possessed predictable molecular weights and very narrow molecular distributions (MWD, M_w/M _n ≤ 1.16). Removal of acetal protective groups from the protected glycopolymer block could yield a hydrophilic block copolymer with pendant glucose moieties. Both protected (lipophilic/CO₂-philic) and deprotected (hydrophilic/CO₂-philic) fluorocopolymers were proven to be CO ₂ amphiphiles.; These CO₂-soluble sugar-containing polymeric amphiphiles have proved to be an effective stabilizer for the heterogeneous polymerization of water-soluble monomers in CO₂. Detailed studies focused on the emulsion polymerization of N-ethylacrylamide (NEAM) in CO ₂. With the aid of such a hydrophilic/CO₂-philic block copolymer, the water-soluble/CO₂-insoluble NEAM could be emulsified and polymerized as a stable latex in CO₂ at 65°C and 352 bar (5100 psi). The resulting submicron-sized poly(NEAM) particles could be obtained even at a very low surfactant concentration (0.2 wt % with respect to NEAM) and the particle morphology was found to be very sensitive to the reaction conditions. Higher temperature, more surfactant and initiator could result in a much smaller particle size. The NEAM emulsion polymerizations were also carried out with varied CO₂ pressures, monomer concentrations, initiators, surfactants with different diblock structures, and chain transfer agent.; Finally, the first microemulsion polymerization in scCO₂ was performed. With the aid of a reported anionic phosphate fluorocarbon surfactant, CO₂-insoluble/water-soluble monomer (acryloxyethyltrimethyl ammonium chloride) and crosslinker (N,N′-methylenebisacrylamide) were dispersed into CO₂ continuous phase within microemulsion water pools. Spherical nano-sized particles with narrow size distributions were obtained.