Radiopaque, Self-Immolative Poly(benzyl ether) as a Functional X-ray Contrast Agent: Synthesis, Prolonged Visibility, and Controlled Degradation.

A self-immolative radiocontrast polymer agent has been newly designed for this study. The polymer agent is composed of a degradable poly(benzyl ether)-based backbone that enables complete and spontaneous depolymerization upon exposure to a specific stimulus, with iodophenyl pendant groups that confer a radiodensity comparable to that of commercial agents. In particular, when incorporated into a biodegradable polycaprolactone matrix, the agent not only reinforces the matrix and provides prolonged radiopacity without leaching but also governs the overall degradation kinetics of the composite under basic aqueous conditions, allowing for X-ray tracking and exhibiting a predictable degradation until the end of its lifespan. Our design would be advanced with various other components to produce synergistic functions and extended for applications in implantable biodegradable devices and theragnostic systems.