Barrier coats versus inert atmospheres. The elimination of oxygen inhibition in free-radical polymerizations

Abstract

SynopsisThe polymerization of UV-curable coatings that react by a free-radical mechanism is subject to oxygen inhibition which can be avoided by utilizing an inert atmosphere. We demonstrate that wax barrier coats used to prevent evaporation of volatile reactive monomers are equally effective in preventing oxygen inhibition. No quantitative difference is found between the degree and rate of polymerization in an inert atmosphere or with a wax barrier coating. However, when used above a given ceiling temperature, the wax barrier allows oxygen diffusion which inhibits cure.

UV‐curing of acrylate thin films onto Al2O3 particles via free‐radical polymerization

“…Of course, utilizing an inert atmosphere for the polymerization is during fluidized bed coating is effective, since it eliminates oxygen inhibition. 19 However, this is prohibitively expensive and impractical in industrialscale fluidization processes. A more practical and useful way is to optimize the formulations of UVcurable chemicals, by using the photoinitiators that are less sensitive to oxygen.…”

How does paraffin wax prevent evaporation of acrylic‐based syrups dedicated to fiber‐reinforced composite processing?

“…It raises critical concerns regarding the composite manufacturing step, especially in the case of open‐mold processes. To prevent MMA evaporation, paraffin wax can be added into acrylic syrups to act as a barrier to vapor . Paraffin wax is a mixture of alkane hydrocarbon molecules generally obtained from oil refining and containing from 18 to 40 carbon atoms (300–600 g mol −1 ).…”

“…Nevertheless, the driving mechanisms of wax‐based evaporation control of solvent‐based syrups have not been much discussed so far. To our knowledge, the only published works were done by Schroeter and Bolon in the 1980s . In these two studies, the authors have investigated wax as antievaporation agent and oxygen inhibitor in several resins, mainly MMA‐based and styrene‐based systems.…”

Oxygen-Mediated Reactions in Photopolymerizable Radical Thin Films: Application to Simultaneous Photocuring Under Air and Nanoparticle Formation

“…Several strategies have been introduced to overcome this unwanted reaction (see in general books and in reviews . Examples include: i) oxygen‐free systems (using nitrogen or carbon dioxide atmosphere), ii) increase of the light intensity or the PI concentration, iii) addition of amines, oxygen scavengers (e.g., triphenylphosphines or phosphites), thiols, cyclic N ‐vinylamides, silanes or organoboranes, borane/amine complexes, sugars, Ti‐ or Zr‐centered compounds, monomers containing some labile hydrogen, crystalline acrylates, UV absorbers and hindered amines, wax barrier coats, iv) use of particular PIs, v) use of singlet oxygen‐generating systems, etc. Oxygen inhibition is somewhat limited under a high light intensity but becomes really detrimental when using low light intensity sources (household LEDs, halogen lamps, fluorescent bulbs, sun…), thin monomer films (where the reoxygenation process is very important) or low‐viscosity media (rate constants of the processes being little limited by the diffusion).…”