Soap-free emulsion polymerization of n-butyl acrylate in aqueous solution in the presence of α- and methylated β-cyclodextrin

Butyl acrylate, a relative hydrophobic monomer, was found to become completely water soluble simply by mixing with either alpha-cyclodextrin or methyl-beta-cyclodextrin. The both cyclodextrins were found to form 1:1 host-guest complexes with butyl acrylate. The complexes formed exhibited similar supramolecular structures, i.e., butyl group of butyl acrylate included in the cavity of cyclodextrins, but the double bond of the monomer locating outside of the cavity. Association constant values for alpha-cyclodextrin and methyl-beta-cyclodextrin were determined to be 407.3 and 45.8 L/mol, respectively, indicating the better fitting of butyl acrylate with alpha-cyclodextrin than with methyl-beta-cyclodextrin. It was found that the addition of either alpha-cyclodextrin or methyl-beta-cyclodextrin, even at very low concentration, could markedly improve the reaction rate, reduce the amount of coagulum, and narrow the molecular weight distribution and particle-size distribution, in which alpha-cyclodextrin exhibited a better effect on polymerizations because of its stronger interaction with the monomer.