Emulsifier-free emulsion copolymerization of styrene and butyl acrylate. I. Kinetic studies in the absence of surfactant

Soapless emulsion copolymerization of styrene (S) and n-butyl acrylate (BuA) has been investigated using two types of initiator and different comonomer feed mixtures. When using K₂S₂O₈ as initiator, the particle size and size distribution of the final latexes (500 nm and 1.003, respectively) is not significantly affected by the comonomer feed composition, whereas the molecular weight and surface characteristics were found to sharply change at high butyl acrylate content. Based on the most probable particle nucleation mechanism and type of chain termination in the monomer swollen particles, a tentative explanation of these results has been proposed. Replacing persulfate by a carboxylic initiator (4-4′-azobiscyanopentanoic acid) results in the formation of stable particles as α observed with the persulfate, provided the aqueous phase pH is fixed in between 6 and 7. Results on the initiator residue location as a function of the conversion point out that the particle flocculation mechanism is strongly significant in the preparation of such latexes.