Application of amphiphilic polysaccharides as stabilizers in direct and inverse free-radical miniemulsion polymerization

Polymeric surfactants were prepared from dextran, a neutral bacterial polysaccharide. Three series of dextran derivatives were studied: neutral dextran derivatives obtained by the attachment of hydrocarbon groups (C6 and phenoxy) to dextran chains, anionic dextran derivatives obtained by further modification of phenoxy-modified dextrans, polylactide grafted dextran copolymers obtained by a well-controlled three-step procedure. Submicronic emulsions (direct or inverse) with a controlled average diameter can be prepared by selecting the operating conditions and the polymeric surfactant used. Polymeric nanoparticles (either bulk polymer or covalent networks swelled by water) were prepared by free-radical miniemulsion polymerization. The surface of the nanoparticles is covered by a physically and/or covalently attached polysaccharide layer. The average size of the latex particles is correlated to that of the initial emulsion droplets provided that the steric stabilization of the initial droplets is enough. The surface coverage of the nanoparticles was investigated and related to the polymerization conditions.