Living and Reactivatable Polymer Networks in Vat Photopolymerisation: RAFT, Photoiniferter and Nitroxide-Mediated Post-Print Growth
Segurola, Juan
2026-08-27 · Report · Version 1.2
Conventional vat-photopolymerised networks are normally treated as chemically finished after printing and post-curing. Residual functional groups can continue reacting, but most propagating radicals terminate irreversibly and the printed object lacks a controlled route for restarting chain growth from defined sites. Photo-controlled reversible-deactivation radical polymerisation provides a different material architecture. Reversible addition-fragmentation chain-transfer chemistry, photoiniferter systems and nitroxide-mediated photopolymerisation can retain or generate dormant reactive species inside a printed network. Subsequent illumination in the presence of an appropriate monomer can reactivate part of that population and enable monomer insertion, photogrowth, covalent welding, surface functionalisation or local chemical reconfiguration. Published demonstrations include visible-light PET-RAFT printing in air, network-bound trithiocarbonate crosslinkers, xanthate photoiniferter formulations that require no separate photoinitiator or photocatalyst, combined radical/cationic RAFT systems, direct-laser-written microstructures with approximately 500 nm features, and an in-situ nitroxide-mediated route extended from two-photon direct laser writing to DLP. These studies establish reactivatability, but they do not demonstrate ideal living polymerisation throughout a heterogeneous crosslinked object. Irreversible termination, optical attenuation, dormant-group degradation, restricted monomer transport, swelling and inaccessible network regions limit the fraction and depth that can be reactivated. This review therefore uses reactivatable network as the primary engineering term and reserves living for the operational terminology used in the cited literature. It proposes evidence requirements and reporting descriptors for distinguishing covalent post-growth from residual cure, swelling, physical coating or ordinary adhesion. The central conclusion is that a printed network should be described as reactivatable only when a defined dormant chemical handle survives printing and produces verified new covalent material during a controlled secondary operation.