Development of a Reactive Force Field for Simulating Photoinitiated Acrylate Polymerization

YH Huang and JJ Karnes and M Shusteff and R Faller, JOURNAL OF PHYSICAL CHEMISTRY B, 127, 5094-5101 (2023).

DOI: 10.1021/acs.jpcb.2c09117

Light-driven and photocurable polymer-based additivemanufacturing(AM) has enormous potential due to its excellent resolution and precision.Acrylated resins that undergo radical chain-growth polymerizationare widely used in photopolymer AM due to their fast kinetics andoften serve as a departure point for developing other resin materialsfor photopolymer-based AM technologies. For successful control ofthe photopolymer resins, the molecular basis of the acrylate free- radicalpolymerization has to be understood in detail. We present an optimizedreactive force field (ReaxFF) for molecular dynamics (MD) simulationsof acrylate polymer resins that captures radical polymerization thermodynamicsand kinetics. The force field is trained against an extensive trainingset including density functional theory (DFT) calculations of reactionpathways along the radical polymerization from methyl acrylate tomethyl butyrate, bond dissociation energies, and structures and partialcharges of several molecules and radicals. We also found that it wascritical to train the force field against an incorrect, nonphysicalreaction pathway observed in simulations that used parameters notoptimized for acrylate polymerization. The parameterization processutilizes a parallelized search algorithm, and the resulting modelcan describe polymer resin formation, crosslinking density, conversionrate, and residual monomers of the complex acrylate mixtures.

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