Control of pore generation and pore size in nanoparticles of poly(styrene-methyl methacrylate-acrylic acid)

Abstract

Seeded emulsion polymerization of styrene-methyl methacrylate-acrylic acid onto seed latexes of monodisperse particles of poly(styrene-methyl methacrylate) was conducted with or without divinyl benzene as a crosslinking agent. Experiments revealed that almost no new particles were formed during the second stage of polymer- ization, and that the seeded latex particles obtained were almost monodisperse. An alkali-acid treatment was then applied to the seeded latex particles swollen in 2-bu- tanone. Experimental results indicated that: (1) for uncrosslinked particles, an opti- mum volume expansion of .50% is reached for a ratio of the swelling agent, 2-bu- tanone, to polymer (methyl-ethyl-ketone/polymer by weight) between 2.0 and 2.9; the volume expansion is much lower outside the above range. (2) For crosslinked particles, the particle volume expansion follows the same pattern, but with smaller values. (3) pH plays an important role in pore generation and volume expansion. Pore generation is optimized by decreasing pH to a value as low as 1.5 during acid treatment, and by keeping pH in the optimum range between 11.98 and 12.20 during alkali treatment. Based on the above observations, a discussion regarding the mechanism of pore gen- eration and particle expansion is provided. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 419 - 426, 1999