We have synthesized amphiphilic triblock copolymers based on a central block of polyacrylic acid (PAA) end-capped with two hydrophobic blocks based on poly(n-butyl acrylate) into which AA units have been incorporated in a statistical way. When dispersed in water, this block copolymer self-assemble within flower-like micelles that bridge into fractal aggregates at higher concentration leading to hydrogels above the percolation concentration (Cp). The exchange time of the hydrophobic blocks within the hydrogels can be varied by decreasing the ionization degree of the over whole AA units from milliseconds up to 108s. We have studied the degradation mechanism of fractal aggregates formed below Cp that are frozen at low pH by diluting them in buffers at higher pH where they turn out to be dynamic. Light scattering measurements show that the size and the molecular weight of the aggregates decrease in a logarithmic way with time. The degradation mechanism does not depend on the final pH. However, its speed displays an exponential variation with the pH which is correlated with the life-time of the hydrophobic blocks.. We have also measured by Confocal Laser Scanning Microscopy (CLSM) the degradation mechanism of frozen microgels (formed above Cp) in the same manner as for fractal aggregates. It appears that microgels are emptied by release of aggregates which results in their swelling and appearance of cracks. Then microgels break-up occurs because the systems have depercolated. The speed of fragmentation can be finely tuned through the pH as for aggregates. As a conclusion, the speed of pH induced degradation of the aggregates and the microgels is strongly related to the ionization degree of their hydrophobic block which makes them interesting as matrix for pH induced delivery of active molecules.

pH induced fragmentation of microgels based on self-assembled triblock copolyelectrolytes

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.