The control of chain‐ends is fundamental in modern macromolecular chemistry for directed one‐to‐one bioconjugation and the synthesis of advanced architectures such as block copolymers or bottlebrush polymers and the preparation of advanced soft materials. Polyphosphazenes are of growing importance as elastomers, biodegradable materials and in biomedical drug delivery due to their synthetic versatility. While controlled polymerization methods have been known for some time, controlling both chain‐ends with high fidelity has proven difficult. We demonstrate a robust synthetic route to hetero and homo α,ω‐chain‐end functionalized polyphosphazenes via end‐capping with easily accessible, functionalized triphenylphosphine‐based phosphoranimines. A versatile thiol‐ene “click”‐reaction approach then allows for subsequent conversion of the end‐capped polymers with various functional groups. Finally, we demonstrate the utility of this system to prepare gels based on homo α,ω‐chain‐end functionalized polyphosphazenes. This development will enhance their progress in various applications, particularly in soft materials and as degradable polymers.

Vinyl esters and carbonates have recently been demonstrated to have considerably lower cytotoxicity than their more commonly used (meth)acrylate counterparts, inspiring their use in the 3D printing of biomaterials. However, the degradation rates of such synthetic photopolymers are slow, especially in the mild conditions present in many biological environments. Some applications, for example, tissue regeneration scaffolds and drug release, require considerably faster biodegradation. Furthermore, it is essential to be able to easily tune the degradation rate to fit the requirements for a range of applications. Herein we present the design and synthesis of hydrolytically degradable polyphosphazenes substituted with a vinyl carbonate functionalized amino acid. Thiolene copolymerization with vinyl esters gave cured polymers which are demonstrated to considerably accelerate the degradation rates of cured vinylester/thiolene polymer scaffolds. Graphical abstract