Photopolymerization acrylonitrile

Polymers in Schemes 12 and 13 were the first examples of the preparation of pyridinium and iminopyridinium ylide polymers. One of the more recent contributions of Kondo and his colleagues [16] deals with the sensitization effect of l-ethoxycarbonyliminopyridinium ylide (IPYY) (Scheme 14) on the photopolymerization of vinyl monomers. Only acrylic monomers such as MMA and methyl acrylate (MA) were photoinitiated by IPYY, while vinylacetate (VA), acrylonitrile (AN), and styrene were unaffected by the initiator used. A free radical mechanism was confirmed by a kinetic study. The complex of IPYY and MMA was defined as an exciplex that served as a precursor of the initiating radical. This ylide is unique in being stabilized by the participation of a... 

Oster [174] proposed the second hypothesis to explain his results on the photopolymerization of acrylonitrile in aqueous solution, buffered at pH 7.0, and sensitized by xanthene dyes and riboflavin using ascorbic acid as the reducing agent. Whereas the monomer is efficiently polymerized when the solution is illuminated in the presence of oxygen, irradiation in its absence leads to photoreduction of the dye to its leuco form but no polymer is formed. Therefore, the author suggests that the leuco dye reacts with atmospheric... 

Photooxidation of Eosin with periodate ion has been used to initiate the polymerization of acrylonitrile in aqueous solution [187]. Addition of acrylonitrile to a periodate solution shifts the absorption maximum from 220 to 280 nm. This spectral change is interpreted as being due to complex formation between the monomer and oxidizing agent. The rate of photopolymerization increases linearly with the absorbed light intensity and monomer concentration. The observed intensity dependence indicates the main chain terminator is not produced photochemically. Polymer is not formed when the concentration of periodate ion is lower than 0.5 mM and the rate of polymerization is independent of its concentration for higher values. 

Feng, Cao, and Li [9] studied the photopolymerization of acceptor monomers initiated by donor initiators, especially by aromatic amines. The proposed mechanism involved a charge-transfer interaction, followed by proton-transfer to produce two kinds of free radicals. The acrylonitrile (AN)/W,V-dimethyltoluidine (DMT) system is shown as an example ... 

Recently, even higher concentrations of trapped radicals have been observed by electron spin resonance. Bamford et al. (5) found up to 1.3 X 1017 radicals per ml., and Ingram et al. (18) found 3.5 X 1017 per ml. in the photopolymerization of acrylonitrile at 20 °C. At the same time, it was found that the concentration was greatly reduced when polymerization was carried out at higher temperatures, and Bamford et al. were unable to detect any radicals at 60 °C. 

The latter mechanism is met in amine-vinyl monomer systems [41-46] (see Scheme 4). Due to the small n-acceptor ability of normal substituted vinyl monomers, an interaction in the ground-state level does not take place. The exciplexes assumed are detectable in aromatic amine-acrylonitrile (AN) systems by their emission spectra, as is shown in Fig. 1 for typical examples. The emission bands at 350 nm (by JV,JV-dimethyl-p-toluidine (DMT)) and 370 nm (by p-phenylene diamine (TMPD) result from the normal fluorescence of the isolated amine. As can be seen, the intensity of the exciplex emission is much higher in the DMT-AN system. This corresponds to the higher polymerization efficiency of that system (<)>[, by A. = 313 nm and 80 K 0.6 for DMT 0.15 for TMPD [46]). Mainly, the much higher dipole moment of DMT (1.1 D) is responsible for this result. The cation radicals [46] or neutral radicals [42] of the amines formed after PET and proton transfer have been detected by ESR measurements. As expected, the rate of photopolymerization of the systems discussed increases with increasing... 

Fig. 2. Monomer conversion by the photopolymerization of acrylonitrile with aniline derivative (1 NJi-dime thylaniline, 2 N-methylaniline, 3 aniline) in dependence of amin concentration (in dimethylformamide, at 30 °C, [acrylonitrile] = 4.88 mol 1 1,...

Some radical initiators decomposing by heat can also be decomposed by UV radiation. Photopolymerization of acrylonitrile in the presence of AIBN or hydrogen peroxide, or of other initiators [75-78] has been reported. The quantum yield of AIBN decomposition is 0.4 at 298 K and 0.6 at 318 K. Photopolymerization of methyl methacrylate, styrene, and vinyl acetate can be initiated by tetramethylsilane, methylchlorosilanes, and halides of Group IV metals [79]. We assume that the radicals are formed by homolytic splitting of the covalent bond... 

Decomposition of initiators can be strongly affected by DA complexes of the initiator with a further component of the system, e. g. the solvent [80], Photopolymerization of acrylonitrile is greatly accelerated by the addition of isobutyl vinyl ether [81], Spectroscopic measurements have shown that acrylonitrile and isobutyl vinyl ether form a donor—acceptor complex which is stable in the dark. When illuminated, it initiates polymerization. 

The accelaration of styrene photopolymerization by oxygen is also explained by excitation of the DA complex of these two substances [82], A copolymer is produced which decomposes upon illumination [83]. Polymerization of methyl methacrylate is initiated by the photoexcited complex of the monomer with triethylaluminium [84]. Methyl methacrylate, acrylonitrile and acrylates in general readily produce unstable DA complexes which decompose to products quite different from the initial components. Methyl methacrylate, for example, polymerizes in the presence of quinoline and bromine. With the monomer, these pairs yield a DA complex which is unstable upon illumination [85a]... 

Cp2TiCl2 has been assessed as additive that controls polymer chain growth in the polymerization of methyl methacrylate.1224 Methyl methacrylate is easily polymerized in the photopolymerization with Cp2TiCl2 in a water-methanol mixture under irradiation of a 15 W fluorescent room lamp. The polymerization proceeded heterogeneously.1225 This process in the presence of 2,2 -bipyridyl, 1,10-phenanthroline, or sparteine as the chelating reagent has been studied.1226 Similar studies on the polymerization of methacrylate monomers such as methyl methacrylate, ethyl methacrylate, phenyl methacrylate, and benzyl methacrylate at 40 °C have also been performed.1227 The results of co-polymerization of methyl methacrylate and acrylonitrile indicate that this process proceeds through a radical mechanism.1228 The mechanism of the controlled radical polymerization of styrene and methyl methacrylate in the... 

The photopolymerization of -vinylcarbazole by perylene-l,4-dicyanobenzene is believed to involve electron transfer. Quantum yields were found to be higher in electron-transfer sensitization than in other systems. One study of interest is the photopolymerization of acrylonitrile by nickel chloride-dimethyl formamide and hydrochloric acid. Unfortunately, the role of the acid could not be explained. 

Photopolymerization of acrylonitrile in the presence of naphthalene and its derivatives,19 of 9-vinylanthracenes,20 and of sulphonyl activators for dye-photosensitized polymerization,21 and the polymerization of MMA photo-initiated by anthraquinone (AQ) and 2-t-butylanthraquinone22 have been reported. Some of the important steps in this latter process are shown in reactions... 

The use of dye-sensitized initiation in polymerization dates to 1949 when Bamford and Dewar observed that some vat dyes could sensitize the photopolymerization of styrene. This was quickly followed up hy Gerald Oster s discovery " in 1954 that the polymerization of acrylonitrile and of acrylamide could be photoinitiated by fluorescein, rose bengal, and similar dyes, in the presence of reducing agents (such as phenylhydrazine, ascorbic acid) and oxygen. Remarkably, the amount of dye required for the photoinitiation event was extremely small ( 0.1% of the weight of monomer), and the quantum yield of monomer consumption was in excess of 4000 monomer units per photon. " ... 

Above equation is based on an analysis that indieates eharge transfer and exciplex formation of acrylonitrile with earbazole forms as the intermediate. Gao et al., carried out kinetie studies of photopolymerization of methyl methacrylate by using piperazine sulfur dioxide eharge-transfer eomplex as a photoinitiator. The polymerization rate (Rp) is dependent on the molar ratio of piperazine to sulfur dioxide, and the eomplex with a eomposition of piperazine to sulfur dioxide in a molar ration of 1 2 is the most effeetive. By using the complex as die photoinitiator, flie polymerization kinetics was expressed as,... 

---