Photopolymerization of Acrylates

The well-known photopolymerization of acrylic monomers usually involves a charge transfer system with carbonyl compound as an acceptor and aliphatic tertiary amine, triethylamine (TEA), as a donor. Instead of tertiary amine such as TEA or DMT, Li et al. [89] investigated the photopolymerization of AN in the presence of benzophenone (BP) and aniline (A) or N-methylaniline (NMA) and found that the BP-A or BP-NMA system will give a higher rate of polymerization than that of the well-known system BP-TEA. Still, we know that secondary aromatic amine would be deprotonated of the H-atom mostly on the N-atom so we proposed the mechanism as follows ... 

Other carboxylate-dye interactions have been reported. Ethylenediamine tetracarboxylic acid (EDTA) and its salts are well known reductants for a variety of dyes (54,55). The amino-acid N-phenylglycine can be photooxidized and induce polymer formation (26,56,57). Studies of the efficiency of photopolymerization of acrylate monomers by MB/N-phenylglycine combinations as a function of the pH of the medium suggest that either the amino group or the free carboxylate can act as an electron donor for the dye excited state, but that the amine functional-lity is the more efficient coinitiator (10). Davidson and coworkers (58) have shown that ketocarboxylic acids are photode-carboxylated by electron transfer quenching of dye triplet states under anaerobic conditions. Superoxide formation can occur when oxygen is present. 

Very recently, the NHC boranes have been used as initiators for the photopolymerization of acrylates [13]. 

In the anthraquinone-sensitized photopolymerization of acrylate monomers, the percent conversion depends markedly on the nature of the solvent as well as on the type of monomer. Ethyl and n-butyl methacrylate, for example. 

Photopolymerization of acrylic monomers and related systems is a challenging area for the application of real-time MIR spectroscopy since the reactions are often completed within seconds, so there needs to be an excellent SNR in the spectra if reliable kinetic data are to be generated. The temporal resolution of an FT-IR spectrometer at a resolution of 16 cm is 11 ms, so 100 spectra can be gathered in the time frame of the fastest reaction, but without multiplexing to improve the SNR. Using a diamond ATR element of area 4 mm that could also be heated to 200 C, uniform irradiation was possible and the cure reactions of films of thicknesses ranging from 1 to 20 pm could be followed (Scherzer and Decker, 1999). 

FTIR spectra are also benehcial in establishing the optimum conditions for curing acrylic adhesives by exposure to UV radiation. The degree of UV polymerization of acrylic adhesives can be followed by the decay of the ethylenic ( CH=CH2) absorption band at 810 cm. Scherzer et al. studied the UV-induced crossUnking of a pressure-sensitive acrylic resin with copolymerized benzophenone groups using variable UV doses and intensities. Real time FTIR spectroscopy was also used to study the effect of various photoinitiators in accelerating the photopolymerization of acrylate resins. ... 

Traditional radical photopolymerization of acrylate-based systems is limited due to several drawbacks such as oxygen inhibition, presence of residual and/or unreactive com-... 

It has been possible to fabricate porous monoliths within silicon [16], glass [17], and polymer [18, 19] microchaimels. Within silica and glass channels, porous monoliths can be fabricated by a thermally aided sol-gel reaction. Photopolymerization of acrylate monomers in the presence of porogens (inert organic solvents) has also been used to obtain porous monoliths. By varying the composition of the monomer blend, the composition of the porogen mixture, and the ratio of monomer to porogen, it is possible to control the porosity of the monolith and the modal size of its pores. In addition, if the channels are made out of acrylate... 

There are also several reports in the literature on use of poly(arylsilanes) as initiators in photopolymerization of acrylic monomers. The photoinitiating efficiency of silane polymers with thioxanthone side groups was found to depend not upon exiplex formation with tertiary amines but rather... 

Dias et al., used, what they called, a hyphenated rapid real-time dynamic mechanical analysis (RT DMA) and time resolved near-infi ared spectroscopy to simultaneously monitor photopolymerization of acrylate coating compositions. This allowed them to determine the rate of conversion and the mechanical properties of the finished films. It is claimed that up to 374 near infrared spectra and to 50 dynamic analysis points can be accumulated within a second. They observed that modulus buildup does not linearly follow chemical conversion of acrylate bonds. The gel point is detected after passing a certain critical acrylate conversion. Their experimental data revealed a critical dependence of the mechanical property development during the later stage of acrylate conversion. 

XIA 14] Xiao P., Fouassier J.P., Lalevee J., Photochemical production of interpenetrating polymer networks simultaneous initiation of radical and cationic polymerization reactions , in Sperling L.H. (ed.), Photopolymerization of Acrylate/Epoxide Blends, Polymers, Special Issue Interpenetrating Polymer Networks , available at http //www.mdpi.com, 2014. 

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