Synthesis of Biomimetic Poly(2-(methacryloyloxy)ethyl phosphorylcholine) Nanolatexes via Atom Transfer Radical Dispersion Polymerization in Alcohol/Water Mixtures

Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) exhibits a phenomenon known as co-nonsolvency in certain alcohol/water binary mixtures. We have exploited this phenomenon to prepare a series of sterically stabilized PMPC nanolatexes by atom transfer radical polymerization (ATRP) under dispersion polymerization conditions using a near-monodisperse poly(ethylene oxide) (PEO) macroinitiator in a 9:1 isopropanol/water mixture. The as-synthesized nanolatex particles comprised nonsolvated PMPC cores and solvated PEO shells, as determined by 1H NMR spectroscopy. In our preliminary experiments linear core-forming PMPC chains were targeted, but alternatively either ethylene glycol dimethacrylate or bisphenol A dimethacrylate can be used as comonomers (at up to 10 mol % based on MPC) in order to prepare cross-linked PMPC particles that acquire swollen microgel character when dialyzed against pure water. Low levels of cross-linker (e.g., 4 mol %) lead to bimodal microgel size distributions as judged by dynamic light scattering. However, higher levels of cross-linker (e.g., 10 mol %) lead to narrow unimodal microgel size distributions, since all the core-forming PMPC chains become cross-linked. The final nanolatex/microgel dimensions are dictated by the target block compositions and initial MPC concentration used in these ATRP syntheses. A PEO113-b-PMPC50 formulation synthesized at 30 wt % solids produced nanolatex/microgel particles that were 5−6 times larger than those observed for the same block composition prepared at 10 wt % solids. TEM and SEM studies confirm that these new sterically stabilized particles have uniform spherical morphologies. Cross-linked PEO-b-PMPC particles were analyzed by X-ray photoelectron spectroscopy after dialysis against water. The surface coverage of the PEO stabilizer chains was estimated to be 54−61%. Aqueous electrophoresis studies confirmed that the PEO-b-PMPC microgels exhibited almost zero net charge, and the addition of electrolyte had little effect on their dimensions and colloidal stability due to the anti-polyelectrolyte behavior expected for the zwitterionic PMPC chains.