Photosensitive micelles based on polysiloxanes containing azobenzene moieties

Photosensitive micelles based on amphiphilic azo-polysiloxanes were obtained and characterized. The amphiphilic polymers were synthesized in a two-step reaction, starting from a polysiloxane containing chlorobenzyl groups in the side chain. In the first step, the polysiloxane was modified with azo-aromatic groups (35–45% substitution degree) and in the second step the unreacted chlorobenzyl groups were quaternized, using different tertiary amines. The structure of the polysiloxanes and their aggregation/disaggregation capacity were evaluated by 1H-NMR, DSC, fluorescence and UV–VIS spectroscopy, dynamic light scattering and transmission electron microscopy. All the amphiphilic polysiloxanes are capable of generating micelles, the critical concentration of the aggregation values being situated in the range 10⁻³–10⁻² g/L. As a function of the ternary amine structure used in the quarterisation reaction, the micellar aggregation process is different, individual micelles or micellar clusters being obtained. The clusters' dimension cannot be controlled, the polydispersity index having high values. The disaggregation processes of the micelles under UV irradiation reveal that the polymer chemical structure influences the aggregates stability. A total micelles disaggregation was obtained for the polysiloxane modified with azophenol and amine containing a long hydrocarbon segment. In the other cases, only a partially disaggregation process takes place.