Azo alkylammonium polyacrylates with one and two alkyl chains: Synthesis and properties

Alkylammonium polyacrylates bearing one or two C10, C12 alkyl chains were synthesized and some of them were modified with a photoisomerizable azobenzene moiety. Differential scanning calorimetry (DSC) measurements and optical microscopy in polarized light investigations reveal a preservation of the liquid crystalline nature in the ionic polyacrylate with two C10 chains, in which methyl orange was incorporated as counterion (0.92 mol azo/100 g polymer) into the pendent ammonium structure. If the azobenzene moiety is introduced by copolymerization of 2-acryloyloxyethyldodecyldimethylammonium iodide or 2-acryloyloxyethyldidecylmethylammonium iodide with 4-acryloyloxyazobenzene, the thermotropic liquid crystalline properties of the copolymers with 0.05 and respectively, 0.01 molar fraction of azo chromophore are slightly affected. The irradiation with UV light (λ: 365 nm) indicates that the trans-cis photoisomerization of azobenzene strongly depend on the azo concentration and the bonding nature in polymer, as well as the molecular structure. Whereas the trans-cis photoisomerization is faster in alkylammonium polyacrylates having azo counterion compared to azo-copolymers, the thermal recovery to initial trans configuration was observed only in the latter.