Synthesis, self-assembly, and characterization of backbone photocleavable polyacylhydrazones

Polymers capable of undergoing rapid degradation after exposure to light irradiation hold great promise in a plethora of applications including biomedical materials, smart coatings and hydrogels, degradable plastics, and others. Herein, the synthesis of new light -degradable polyacylhydrazones comprising alternating hydrophilic poly(ethylene glycol) (PEG) segments and hydrophobic aromatic units, are presented. A polycondensation reaction between diacylhydrazide terminated poly (ethylene glycols) ( M n = 4000 and 1500 g mol -1 ) with aromatic dicarbonyl comonomers was employed for the synthesis of the amphiphilic polyacylhydrazones. By increasing the number of aromatic moieties in close proximity to the acylhydrazone bonds and varying the type, dialdehyde vs diketone, and the conjugation length of the hydrophobic comonomers, the absorption maximum of the copolymers was shifted to longer wavelengths. The amphiphilic polyacylhydazones derived from the PEG with M n = 4000 g mol -1 self -assembled in water into spherical nanoparticles, evidenced by SEM and DLS. Finally, light irradiation of the polymer assemblies induced the photocleavage of the acylhydrazone bonds along the polymer backbone, which led to the dissociation of the polymer nanoparticles and the formation of a PEG derivative as the main photoproduct.