Combined Ultraviolet, Vacuum and Thermal Exposure of Photopolymers: Synergistic Ageing and Test Equivalence

Ultraviolet and vacuum-ultraviolet photons can cleave polymer bonds and modify near-surface chemistry, while vacuum promotes outgassing and thermal cycling drives repeated expansion mismatch and crack opening. When these stresses are combined, the sequence of exposure can change the result: outgassing before irradiation alters available low-molecular species, irradiation can embrittle a surface before thermal cycling, and temperature changes reaction and diffusion rates. Photopolymer networks are especially sensitive to cure conversion, residual monomer and oxygen-inhibited surface layers, so state definition is essential before accelerated testing. ER-383 treats test equivalence as a mapping problem between spectral irradiance, absorbed dose, pressure, specimen temperature, number of cycles and material response. It rejects simple hour-for-hour acceleration and requires at least one response-based bridge between separate and combined exposures.