Thick-Section Photocuring of Putties, Gels, Sealants and Potting Compounds: Attenuation, Frontal Cure, Exotherm and Through-Cure Qualification

Photocuring ceases to be a surface-coating problem when the optical path becomes comparable with the attenuation length of the formulation. In a thick putty, gel, sealant or potting mass, the exposed surface can reach a high apparent cure state while an intermediate layer or core remains chemically and mechanically different. Increasing irradiance or exposure time does not guarantee that this gradient disappears, because absorption, scattering, photoinitiator depletion, photobleaching, oxygen transport, vitrification, heat generation and any secondary cure mechanism evolve during exposure. ER-185 treats through-cure as a spatial qualification problem. The engineering question is not whether light can start polymerisation, but whether every region that carries a required function reaches an accepted final state without unacceptable thermal, dimensional or chemical gradients. The review separates ordinary Beer-Lambert attenuation from photobleaching-assisted cure fronts, and both from thermally self-propagating frontal polymerisation and dual-cure chemistry. No published thickness, dose, wavelength, photoinitiator level or temperature is transferred as a universal design rule.