Soap-free emulsion copolymerization of methyl methacrylate-butyl acrylate with sodium α-olefin sulfonates as functional monomer

Sodium salt of alpha-olefin sulfonates (AOS) a mixture of sulfonated unsaturated linear hydrocarbon with carbon numbers from C12 to C14, is used in methyl methacrylate/butyl acrylate (MMA/BA) soap-free emulsion copolymerization. The reactivity ratios of AOS-MMA are determined to be r(A) = 1.98 and r(M) = 0.034 for AOS and MMA respectively. In order to assure distribution of AOS units on the out-shell layer of the particles, a semi-continuous emulsion polymerization is used. Latex of high solids of up to 60% has been obtained with 5% AOS. And with 1% AOS, latex solids can reach to 45% with good stability, whereas this value is limited to 40% with sodium dodecyl sulfate (SDS) as surfactant. The particle size is in constant increase with latex solids combined with a sharp decrease in particle number when AOS is used; while the particle size and number of particles are kept relatively constant when SDS is used as surfactant. This is attributed to the fact that SDS can either adsorb on or desorb from the particle surface, and AOS would be fixed on a position on the particle surface once copolymerized with MMA and BA. The AOS prepared latex also shows a narrower particle size distribution, and the latex with 35% is stable after a shelf standing of up to one year.