Synthesis, photoresponsive behavior, and self-assembly of poly(acrylic acid)-based azo polyelectrolytes

A series of novel azo polyelectrolytes have been synthesized based on an extremely reactive precursor polymer, poly(acryloyl chloride) (PAC), prepared from acryloyl chloride by radical polymerization. The precursor polymer was post-functionalized by the Schotten-Baumann reaction of PAC and several aromatic azo reactants containing hydroxyl end groups. The degrees of functionalization were controlled by selecting suitable feed ratios between the azo reactants and poly(acryloyl chloride) and the unreacted acyl chloride groups were hydrolyzed to obtain ionizable carboxyl groups. The products were characterized by elemental analysis, FT-IR, H-1 NMR and UV-vis spectroscopy. Irradiated by 365 nm UV light, azo polyelectrolytes PPAPE, PEAPE and PCAPE showed a significant photochromic effect. The contact angles of water on the surfaces of spin-coated films of PPAPE and PEAPE decreased evidently upon UV irradiation. The extent of the photoinduced contact angle changes depends on the type of the azo chromophores and the degree of functionalization. Self-assembled multilayers of the azo polyelectrolytes were fabricated by a layer-by-layer adsorption method. A significant photochromic effect from cis-trans isomerization of the azo chromophores was observed for the multilayers. The photoinduced contact angle changes of water on the self-assembled multilayers were also observed.