Synthesis and Self-Assembly of Block Polyelectrolyte Membranes through a Mild, 2-in-1 Postpolymerization Treatment

Block polymer systems containing spatially separated positive and negative charges are desirable for a number of applications, including biomedical devices, membrane separations, and coatings. Unfortunately, the tendency of positive and negative block polymers to charge cancel and form an insoluble coacervate precipitate leads to processing difficulties in the fabrication of charged thin films. We use postpolymerization modifications to simultaneously add both negative and positive charges to self-assembled neutral ABC triblock polymer thin films. Using reversible addition-fragmentation chain transfer polymerization, we synthesized triblock terpolymers consisting of poly(n-propyl styrene sulfonic ester), poly(4-chlorostyrene), and poly(vinylbenzyl chloride). The chemical functionalization of both charged blocks was accomplished simultaneously through exposure to gaseous trimethylamine in a single step at room temperature, simplifying the synthetic procedure and preserving the microstructure of the thin film. The quantitative functionalization was tracked through attenuated total reflectance infrared spectroscopy, and the thin film morphology was evaluated using intermodulation atomic force microscopy, transmission electron microscopy, and grazing-incidence small-angle X-ray scattering.