Synthesis of biocompatible sterically-stabilized poly(2-(methacryloyloxy)ethyl phosphorylcholine) latexes via dispersion polymerization in alcohol/water mixtures.

Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) is soluble in either 2-propanol or water but becomes insoluble in certain alcohol-rich 2-propanol/water mixtures. We have exploited this unusual cononsolvency behavior in order to prepare new biocompatible sterically stabilized PMPC latexes via nonaqueous dispersion polymerization in 2-propanol/water mixtures. All polymerizations were conducted in the presence of monomethoxy-capped poly(ethylene glycol) methacrylate (PEGMA) as a reactive stabilizer, with some formulations including ethylene glycol dimethacrylate (EGDMA) as a cross-linker. Under optimized conditions, unimodal size distributions could be obtained with a mean latex diameter of approximately 1 microm, as judged by laser diffraction and DLS. The mean latex diameter depended on both the PEGMA and initiator concentration but was almost independent of the cross-linking density. Smaller PMPC latexes were obtained by increasing the alcohol content of the dispersion medium. On dilution with water, these latexes acquired microgel character. The microgel solution viscosity was insensitive to added salt due to the so-called "antipolyelectrolyte" effect, which is characteristic of polyzwitterions. Finally, copolymerization of MPC with a fluorescein-based methacrylic comonomer produced fluorescently labeled PMPC latexes, which may have potential biomedical applications.