In free radical emulsion polymerization, water soluble initiator radicals are generated by either a thermal or redox process. The free radicals in the aqueous phase will react with soluble monomers until they reach a composition (z-mer radical) which favors entry into a surfactant micelle, resulting in particle nucleation, or adsorption onto a pre-existing particle to carry out the intended chain propagation. Some oligomer radicals may also be terminated in the aqueous phase before such adsorption events, forming serum oligomers which can be found in the final product. It is apparent that understanding the serum phase oligomers is not only important to probe the aqueous phase reaction during emulsion polymerization, but also to ascertain their impact on the final performance of emulsion products. A gradually fed, seeded butyl acrylate/acrylic acid emulsion with redox activated persulfate initiator was studied. The serum phases of in-process samples were analyzed by GPC-RI/MS to determine the concentration, the molecular structure, and the formation mechanism of the serum phase oligomer as well as soluble radicals during the emulsion polymerization. The z-mer radicals captured by 4-hydroxy-TEMPO were also identified in the analysis and their composition is in good agreement with the composition of sulfate anion free radical adducts suggested by Maxwell, I. A. et al. based on hydrophobic free energy of absorption1. 1. Maxwell, I. A.; Morrison, B. R.; Napper, D. H.; Gilbert, R. G. Macromolecules, 1991, 24, 1629-1640

Probing serum phase oligomer in acrylic emulsion polymerization process by GPC-RI/MS

249th National Meeting (2015)

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