Emulsion polymerization of hydrophobic monomers like stearyl acrylate with cyclodextrin as a phase transfer agent

In emulsion polymerization also water insoluble hydrophobic monomers like stearyl acrylate can be used if cyclodextrin is added as a phase transfer agent. The characterization of the corresponding emulsion polymers by thermal analysis with DSC, by molecular weight determination with SEC and by measuring particle size distribution, particle density distribution (i. e. chemical composition and heterogeneity) and free cyclodextrin molecules in the aqueous phase with the analytical ultracentrifuge provides first indications for the following mechanism: An especially high transfer resistance exists for longer alkyl chains containing molecules at the interface between the monomer droplet and the water phase resulting in a concentration decrease in the polymerizing particle. Therefore, it is assumed that cyclodextrin and its ability to form a water soluble complex with hydrophobic molecules reduce the kinetic barrier and makes it easier for the stearyl acrylate to leave the monomer droplet. After arriving at the surface of the growing particle, the stearyl acrylate is released from the complex and able to enter it. Now the free cyclodextrin can start its transport function again. Only 5 wt.-% of cyclodextrin is necessary to polymerize almost 100% of stearyl acrylate.