Water soluble poly(styrene sulfonate)-b-poly(vinylidene fluoride)-b-poly(styrene sulfonate) triblock copolymer nanoparticles

Abstract

A visible light, Mn₂(CO)₂-photomediated process was used to enable the iodine degenerative transfer controlled radical polymerization of vinylidene fluoride (VDF) initiated from I–(CF₂)₆–I, and the successive quantitative activation of the ∼CH₂–CF₂–I and ∼CF₂–CH₂–I chain ends of I–PVDF–I, to produce a series of PNpSS-b-PVDF-b-PNpSS triblock copolymers (NpSS/VDF/NpSS = 4/60/4, 15/60/15, 34/60/34) with neopentyl styrene sulfonate (NpSS), which upon NaN₃ deprotection, afforded the corresponding PNaSS-b-PVDF-b-PNaSS. All blocks, as well as PVDF, PNpSS and PNaSS formed water stable dispersion/solutions following either nanoprecipitation from acetone (PVDF, PNpSS, and PNpSS-b-PVDF-b-PNpSS) or direct dissolution in water (PNaSS, PNaSS-b-PVDF-b-PNaSS). Remarkably, all PNaSS-b-PVDF-b-PNaSS triblocks also provided indefinitely stable systems even under the high ionic strength conditions of phosphate buffered saline (PBS) solutions, corresponding to cell-isotonic, pH = 7.4 conditions. These trends were found to be consistent with the block composition dependence of the apparent hydrodynamic radius (R_h), conductivity, and zeta potential (ζ), where R_h increases upon deprotection from about 35–25 nm to about 168–136 nm in water, and decreases to 133–86 nm in PBS solutions, ζ decreases from ∼−40 mV to ∼−70 mV in water and increases to ∼−18 mV in PBS, and where the conductivity is negligible for PNpSS-b-PVDF-b-PNpSS but then increases linearly to ∼0.2 mS cm⁻¹ for PNaSS-b-PVDF-b-PNaSS in water to reach ∼17 mS cm⁻¹ in PBS. Finally, the blocks were evaluated as promising ¹⁹F-MRI contrast agents.