The complex emulsion/solvent evaporation technique was employed for the production of water-containing polymer microcapsules. The inner phase of the microcapsules consisted of an aqueous solution of gelatin. Several polymers (e.g. poly(styrene), poly(methyl methacrylate), ethyl cellulose, poly(vinyl chloride)) were utilized as wall-forming materials and the effect of the polymer type on the size and the surface characteristics of the microcapsules was experimentally investigated. The size of the microcapsules was strongly affected by the conditions applied during the formation of both simple (w/o) and complex (w/o)/w emulsions. Poly(styrene) microcapsules with a mean Sauter diameter in the range of 4-12 microns were prepared by varying the rate of agitation (1500-4000 rpm) and the concentration of stabilizer (potassium oleate, 0.1-1.5% w/v) used in the formation of the (w/o)/w emulsion. High stabilizer concentrations and agitation rates resulted in a significant reduction of the mean size of the complex droplets and in a simultaneous increase of the breadth of the capsule size distribution.
Compositional analysis of a series of free-radical emulsion polymerized styrene/2-ethylhexyl acrylate copolymers following close to random polymerization statistics was accomplished by elemental analysis, UV and IR. A satisfactory agreement was obtained between the three independent techniques. IR calibration curves were constructed based on sequence-independent infrared absorption bands determined by plotting peak intensities against the number fraction of each of the possible monad, dyad and triad structures in the copolymers. The intensities of the skeletal ring breathing vibration of styrene units at 1602 cm8 as well as the C -0 stretching vibration of the saturated ester group of 2-ethylhexyl acrylate units at 1 158 cm-' were shown to be representative of the copolymer com osition, whereas the position and shape of the carbonyl stretching band at 1730 cm-were shown to depend on both the composition and the monomer sequence distribution. A calibration curve not requiring the use of an internal thickness band was obtained by plotting the ratio of absorbances of the 1602 cm-' and the 1 158 cm-' peaks as a function of the mole ratio of the corresponding monomers in the copolymer.
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