Synthesis of poly(glycerol adipate)-g-oleate and its ternary phase diagram with glycerol monooleate and water

Poly(glycerol adipate) (PGA) was synthesized by enzymatic polymerization and grafted with different amounts of oleoyl chloride. A series of graft copolymers PGA-g-Ox was obtained where O represents the oleate side chains and x is the degree of grafting (mol% of the pendant OH groups of PGA esterified) ranging from 11 to 90. Small angle X-ray scattering (SAXS) data revealed nanophase separation of the oleate side chains into nanodomains in bulk and wide angle X-ray scattering (WAXS) profiles showed a broad halo, reflecting the amorphous nature of the synthesized graft polymers. Glycerol monooleate (GMO), an amphiphilic lipid with one hydrophobic oleate tail and a glycerol hydrophilic head group, self-assembles into various liquid crystalline phases in the presence of water. Since oleate chains are integral part of both GMO and the graft copolymers, a certain degree of miscibility can be expected influencing the self-assembly behavior. Using SAXS for phase identification, systematic studies were carried out at room temperature on the ternary system of GMO/PGA-g-O22/water and the ternary phase diagram was constructed. The addition of polymer did influence the phase behavior of the GMO/water system. The water in the lamellar and cubic mesophases was partially replaced by PGA-g-O22. Furthermore, keeping the GMO/water ratio constant at 1:1, the addition of PGA-g-O22 lead to swelling of the water channels in the inverse bicontinuous Pn3m cubic phase. Preliminary investigations on the potential application of PGA-g-O22 as a stabilizer of structured nanoparticles in aqueous dispersions were carried out employing different transmission electron microscopy techniques.