Synthesis and characterization of nonaqueous dispersion particles with photolabile alpha-heptadecylphenacyl ester stabilizer chains

We describe a new method for the synthesis of core-shell photolabile nanopa rticles. The synthesis begins with the batch emulsion copolymerization of n -butyl methacrylate (BMA) and ethylene glycol dimethacrylate to form small (20-nm-diameter) crosslinked particles with a narrow size distribution. The se seeds are then used for a second-stage emulsion copolymerizations in whi ch BMA and various polar monomers, including methacrylic acid, are added un der monomer-starved conditions. After characterization of the particles, th ey are transferred to an N,N-dimethylformamide solution. The cesium salt of the carboxylic acid groups is reacted with 2-bromo-1-phenyl-octadecan-1-on e to convert various fractions of the -COOH groups to the corresponding 2-b enzoylheptadecyl ester groups. These aliphatic ester groups render the surf ace sufficiently hydrophobic that the particles can be dispersed in common aliphatic hydrocarbons solvents to yield colloidal dispersions, sterically stabilized by the dangling aliphatic chains. Ester groups with a phenyl ket one attached to the P-carbon are photolabile. Irradiation of the particles with W light detaches the sterically stabilizing chains from the particle a nd transforms the surface groups back to COOH groups. This leads to floccul ation of the particles. The emphasis in this article is on the optimization of the particle synthesis and the characterization of the particles obtain ed. (C) 2001 John Wiley & Sons, Inc.