Transcarbamoylation and Urethane-Exchange Networks in Photocurable Materials: Catalysis, Creep, Repair and Reprocessing

Urethane and carbamate exchange reactions can convert permanently crosslinked polyurethane-like photopolymers into networks that relax, repair or reprocess at elevated temperature. The relevant chemistry includes catalyst-promoted urethane-urethane exchange, hydroxyl-mediated transcarbamoylation, hindered-urea pathways that generate or exchange urethane bonds, and related covalent adaptable network architectures. This review distinguishes the photochemical step that fixes printed geometry from the thermal or chemical exchange processes that subsequently change network topology. The central engineering problem is separation of timescales: the printed part must remain dimensionally and mechanically stable during service, yet exchange must become sufficiently fast under a controlled repair or reprocessing treatment. Published polyurethane-vitrimer and photo-printable dynamic-network studies show that catalysts, free hydroxyl content, steric environment, temperature and network architecture strongly affect stress relaxation and recyclability. However, fast relaxation can also increase creep, catalyst residues can alter ageing, and post-print exchange may change shape as well as properties. A qualification framework is proposed around exchange-mechanism identification, relaxation and creep, thermal history, catalyst retention, recovery efficiency, dimensional fidelity and repeated reprocessing cycles.

ER-316 · Version 0.6.