Poly(methyl methacrylate) (PMMA) and PMMA copolymers derived from plant oils (Polylinseed oil-g-PMMA, Polysoybean oil-g-PMMA, Polylinoleic acid-g-PMMA (PLina-g-PMMA) and Polyhydroxy alkanoate-sy-g-Polylinoleic acid-g-PMMA (PHA-g-PLina-g-PMMA)) as hydrophobic polymers, a series of hydrophobic microsphere or nanosphere dispersions, were prepared by the emulsion/solvent evaporation method. The diameters of the nanospheres and microspheres were measured by dynamic light scattering with a zetasizer, optically and by scanning electron microscopy. The magnetic quality of the microspheres was determined by the electron spin resonance technique. Acetylsalicylic acid (aspirin, ASA) was used as a model drug and loaded into the microspheres during the preparation process. The effect of the stirring rate over the size and size distribution of the micro/nanospheres was evaluated, and the effects of copolymer types derived from plant oil/oily acids and the copolymer/drug ratios were evaluated. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1610-1618, 2011