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The nature of photopolymer materials considerably depends on their solidification extent, which can be altered only by the formulation photoactivity and external light intensity. Herein, an underlying internal microdomain regulatory (IMR) mechanism for the modulation of photopolymerization behaviors and material properties based on tunable upconversion luminescence is reported. The results revealed that the regulatory mechanism is dependent on the dispersion and photophysics of the upconversion particles (UCPs). Such particles as inner illuminators initiating near-infrared (NIR) photopolymerization can be tuned by a time-sharing hydrothermal reaction with sizes ranging from 5 to 40 μm for continuous variations of UCP distribution patterns and luminous efficiency in the photosensitive medium. The enhancement of upconversion luminescence exhibits a significant size dependence, allowing the photopolymerization process to begin near a single UCP for continuously controlling microdomain kinetics. UCPs with ∼40 μm have excellent dispersion and size-saturation luminescence intensity. These UCPs possess the widest range of microdomain gradient variation (0–45% in 130 μm) due to the IMR mechanism. Moreover, the uniquely controllable mechanism delays the conversion corresponding to the gel point (Cgel), allowing for greater polymer chain relaxation to release the shrinkage stress and improve the mechanical properties of the materials. The proposed IMR provides an unparalleled regulatory dimensionality for photopolymer performances and expands the prospects of photopolymerization technology in high-performance materials manufacturing.
Zou et al. (2024) studied this question.