Efficiency of 2,2‐dimethoxy‐2‐phenylacetophenone for the photopolymerization of methacrylate monomers in thick sections

Abstract

The efficiency of 2,2-Dimethoxy-2-phenylacetophenone (DMPA) for the photopolymerization of methacrylate monomers in thick sections was assessed. DMPA is an efficient photoinitiator for thick sections (%2 mm) because a fast reaction and high conversions are obtained with concentrations as low as 0.25 wt % DMPA. The polymerization rate increased when the DMPA content increased from 0.125 wt % to 0.25 wt %. However, the conversion versus irradiation time profiles in resins containing 0.25 wt % or 0.5 wt % DMPA were similar. This is attributed to the screening effect caused by excessive levels of DMPA. In addition, the consumption of DMPA under UV irradiation was accompanied by the appearance of light absorbing photoproducts. Because the absorbing species nearest to the light source absorb part of it, the light fails to reach the deeper layers of the sample. The overall effect of light screening is a reduced photoinitiation rate and double bond conversion along the irradiation path. This effect was compensated by the use of irradiation sources of higher intensity; which increased the initiation rate by increasing the production of primary radicals. DMPA is colorless and it does not require the presence of amine as coinitiator. These properties make DMPA attractive as photoinitiator of dental composites.

Renewable sulfur-containing thermoplastics via AB-type thiol-ene polyaddition

“…When sufficiently high intensity UV-sources are used (in our case 2 W cm -2 ), the whole process of polymerization is finished in a matter of minutes. [29] Thermal initiation, on the other hand, generates radicals that are equally distributed in the polymerizing liquid, which inevitably leads to lower local concentration of radicals, compared to photochemical initiation, even when both the thermal and photochemical initiators show equal half-lives under the applied reaction conditions. This was confirmed by a 500 MHz 1 H-NMR analysis of P3, showing an overall disulfide content of 0.68%, which is significantly less than half of the disulfide content compared to the photo-polymerized polymer P2.…”

Photocross‐linked polymers based on plant‐derived monomers for potential application in optical 3D printing

“…DMPA molecule generates two reactive free radicals which initiate radical polymerization . It was determined earlier, that 3 mol% was an optimum concentration of DMPA to initiate the photopolymerization of acrylates …”

Methacrylate and Epoxy Resins Photocured by Means of Visible Light-Emitting Diodes (LEDs)

“…Scheme 15.3 shows the decomposition of 2,2-Dimethoxy-2-phenylacetophenone (DMPA) under irradiation with a LED (peak wavelength at 365 nm). 16 Norrish type-II photoinitiators undergo a bimolecular reaction where the excited state of the photoinitiator interacts with a second molecule (a coinitiator) to generate free radicals. The behavior of a Norrish type-II photoinitiator, such as the ketone/amine (AH) pair, in the presence of monomer (M) can be represented by the following simplified reaction scheme:…”