Azo-Containing Polymers with Degradation On-Demand Feature

Molecules comprising aliphatic azo moieties are widely used as radical polymerization initiators, but only a few studies have explored their usefulness as stimuli-responsive motifs in macromolecular constructs. The controlled degradation of azo-containing polymers has indeed remained largely unexplored. Here we present the syntheses of linear azo-containing polyamides and polyurethanes and report on their thermally and optically induced responses in solution and the solid state. We show that the stimuli induced degradation behavior depends strongly on the nature of the polymer backbone, the state of matter, and in solution, on the nature of the solvent. The stimuli-responsive solid-state properties of the azo-containing materials may be particularly useful. In the case of the polyurethanes studied here, temperature- or light induced cleavage of the azo motifs led to a controllable decrease in the molecular weight, which, in turn, caused a reduction of the elongation at break, modulus, and strength. The controlled degradation of the polymer in well-defined areas can be readily achieved via photopatterning, and this approach was shown to be useful to produce solid structures with graded mechanical properties.