Dynamic Polymer Binder with Light-Regulated Molecular Weight via Addition-Fragmentation Chain Transfer for Holographic Recording

Dynamic covalent chemistry was employed to improve the holographic grating performance by facilitating diffusion of monomers and network rearrangement in a holographic photopolymer system. Because of the high degree of spatiotemporal control afforded by the radical-mediated addition???fragmentation chain transfer reaction between allyl sulfide (AS) moieties and thiols, this chemistry proved well -suited for the formation of high-quality holographic photopolymers. Through exchange with a monofunctional thiol, polymer chains incorporating AS along the backbone exhibited a decrease of molecular weight of more than 80% upon the light exposure. The dramatic molecular weight reduction resulted in a corresponding viscosity drop of the whole resin system up to 1 order of magnitude. To take advantage of the covalent bond exchange, the polymers with AS (termed AS polymers) functional groups were utilized as ???dynamic binders??? in thiol???ene based holographic photopolymers designed to delay and reduce the viscosity increase of recording media during the holographic exposures. Such light-regulated viscosity reduction was found to greatly improve the recording formulations with limited diffusion of monomer during the recording. The systems utilizing AS polymer demonstrated a notable improvement of the refractive index modulation as large as 70% compared with the nondynamic analogue. Additionally, the haze in these dynamic systems was almost unchanged compared to control groups where no exchange occurred.

Automated summary

Dynamic covalent chemistry was employed to improve the holographic grating performance by facilitating diffusion of monomers and network rearrangement in a holographic photopolymer system. The radical-mediated addition-fragmentation chain transfer reaction between allyl sulfide (AS) moieties and thiols provided high spatiotemporal control, making it well-suited for high-quality holographic photopolymers. The exchange with a monofunctional thiol resulted in a significant decrease in molecular weight and viscosity, improving the recording formulations with limited diffusion of monomer and demonstrating a notable improvement of the refractive index modulation.