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The use of photoinitiators in initiating the free-radical and cationic curing of reactive monomer systems is essential in ensuring efficient 12 While it is possible to use very high intensity radiation to induce self curing without adding small molecule photoinitiators, the rate and extent of curing will be low. This not only leads to long curing times, but also results in incomplete conversion of the monomer functional groups. There have been numerous efforts to attach conventional photoreactive groups to polymerizable monomers. This results in incorporation of the initiating group being appended to the monomer in the final cured network. However, since only a small fraction of the photoreactive groups are actually consumed in the photouring process, the reactive groups remain on the side chain of the polymer network and may still undergo additional photochemical reactions during the service life of the coating or film. This is particularly troublesome when the coating or film will be subjected to outdoor radiation from sunlight since the reactive groups are designed to have absorption between 300 and 400 nm. As suggested by the discussion above, curing systems of reactive monomers that can both initiate polymerization as a photoinitiator and participate in the subsequent polymerization would be attractive. This would be particularly true if the monomer initiator were to bleach or lose its absorption when copolymerized into the forming polymer matrix. To this end, monomer initiators based on maleimides have been 34 In an interesting 3 a difunctional monomer with both a maleimide and an acrylate reactive group on the same molecule was photopolymerized without the need of adding an external photoinitiator. It has also been reported that vinyl acrylate can self-initiate its own free-radical polymerization as well as the free-radical polymerization of acrylate 6 The unique conjugation provided by the vinyl group and the structure of the acrylate provides for a red-shifted absorption spectrum. Consequently, vinyl acrylate can be excited at wavelengths approaching 300 nm. Unfortunately, vinyl acrylate has a high vapor pressure at room temperature and is not adaptable to practical use. It would be expected that compounds having a similar structure to vinyl acrylate with higher molecular weight and more conjugation would be less volatile and exhibit enhanced initiation efficiency and red-shifted UV absorption behavior. In this paper, results are given for the characterization of new monomer initiators designed under the assumption that vinyl esters with similar molecular structure to that of vinyl acrylate will also be capable of initiating polymerization, with the advantage of being less volatile. The initiating efficiency and photopolymerization of these monomers are reported. The initiating radical species have been identified by trapping using a nitroso free-radical trap.
