Blue light was provided by a collimated, light-emitting diode (LED)–based illumination source (Thorlabs M470L3-C1) with an emittance centered at 470 nm (full width at half maximum, 25 nm), used in combination with a current-adjustable LED driver (Thorlabs LEDD1B) for intensity control. UV light was provided by a UV spot curing system (OmniCure LX500, Excelitas Technologies) equipped with an OmniCure LED MAX head with an emittance centered at 365 nm. Irradiation intensities were measured with an International Light IL1400A radiometer equipped with a GaAsP detector (model SEL005), a 10× attenuation neutral density filter (model QNDS1), and a quartz diffuser (model W).

Resin formulations were introduced between NaCl crystal windows (International Crystal Laboratories) separated by spacers (26 μm thick for bisGMA/TEGDMA, 51 μm thick for BPAEDA, and 13 μm thick for NPM/TEGDVE to maintain constant sample thickness during polymerization). Each sample was placed in a Thermo Scientific Nicolet 6700 Fourier transform infrared (FTIR) spectrometer equipped with a horizontal transmission accessory, as described previously (30), and spectra were collected from 650 to 4000 cm−1 at a rate of 2 per second. The functional group conversion upon irradiation was determined by monitoring the disappearance of the peak area centered at 1635 cm−1 for the methacrylate stretch, 1636 cm−1 for the acrylate stretch, 1618 cm−1 for the vinyl ether stretch, and 829 cm−1 for the maleimide C==C double bond stretch. The respective sample thicknesses for the formulations were chosen to ensure that the functional group peaks remained within the linear regime of the instrument detector while affording good signal-to-noise ratio and maintaining optically thin and isothermal polymerization conditions. All experiments were performed in triplicate, and the photoinitiator and photoinhibitor concentrations and irradiation intensities were as indicated in Materials and Methods and figure legends.

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