N-alkyl Maleimides: Syntheses And Application As Photoinitiator

This work is about the syntheses of N-alkyl maleimides and their applications as photoinitiators for photo polymerization and photo curing. Four synthesis methods for N-alkyl maleimides were compared. Among them the method using xylene to dehydrate by one-step reaction was found to be the best. Six N-alkyl maleimides were prepared with yield from 25% to 55% by this method. The structures and properties of these Mis were characterized by FTIR, 1H-NMR, UV spectra, melting point and refractive index.The effects of MI structure and concentration, reactive diluents, additives and resins on photo curing initiated by MI were studied by the gel conversion and photo-curing rate. The results showed that the photo-curing rate was proportional to the square root of Mi's concentration. Vinyl acetate was not a reactive mono-functional diluent for the photo curing of difunctional acrylic aliphatic polyurethane initiated by MI. As the electronic absorption of Styrene covered the main range of absorbencies of MI in UV spectra, MI cannot initiate the photo polymerization for the system containing styrene. Compared with TPGDA, HDDA was found more reactive for the photo curing of acrylic aliphatic polyurethane. The photo curing was sensitized by tertiary amines. The effects of sensitization was found in the order: methyl diethanol amine > dimethyl ethanol amine > triethyl amine. At low concentration, the acrylate containing tertiary amine group can also enhance the photo curing reaction. Chloroacetic acid and ethyl chloroacetate were also found effective in increasing the photo-curing rate. Vinyl ether monomers* can also increase the photo-curing rate when their concentration was at relatively low level. The aliphatic difunctional acylated polyurethane was found more reactive than difunctional acrylated epoxy resin toward the photo initiation of MI.The effects of MI on the photo stability and ageing of PVA, PS and photo-curedfilm containing MI component were studied. The results showed that the molecular weight and their distribution of PVA-1788 and PS were not changed greatly by UV irradiation after addition of MI, while for PVA-1799, molecular weight increased after irradiation. MI also improved the anti-cracking and minimized the color changes of the cured film in the photo ageing experiments. At the same time, MI had little effect on the hardness and thermal stability of the cued film.