Photopolymerization of methyl methacrylate

However, no independent evidence is presented for the existence of this complex. In our view a simpler explanation for the lack of reaction in unbuffered solution is that the nondissociated form of ascorbic acid is a chain terminator. At the typical concentrations employed, 1-10 mM, more than 90% of ascorbic acid (pK = 4.1) is not dissociated when dissolved in pure water. At pH 6.0 only 1% is present as the protonated form. Furthermore, in their study of the photopolymerization of methyl methacrylate initiated by acriflavine-ascorbic acid, Lenka and Mohanty [180] report the rate of polymerization reaches a maximum when the ascorbic acid concentration is approximately 10 mM. The decrease in polymerization rate at higher concentrations suggests ascorbic acid participates in chain transfer and/or termination reactions. 

Recently Fouassier and Chesneau [219] studied the photochemistry of the system Eosin-PDO-MDEA in aqueous acetonitrile using steady-state irradiation and laser flash photolysis. The photopolymerization of methyl methacrylate (MMA) sensitized by the photoreduction of Eosin is investigated in acetronitrile to understand the mechanism of initiation and the enhancement in the rate of polymerization caused by the presence of PDO, 3. Rates, quantum yields of photopolymerization, and number average molecular weights of the polymer are determined with MMA (7 M), Eosin (3 x 10 5 M), and MDEA (0.1 M) in the presence and in the absence of 2 x 10-3 M PDO. 

TABLE 9 Photopolymerization of Methyl Methacrylate Sensitized by Eosin"... 

A more efficient photoinitiator has been designed by combining the Eosin-MDEA system with diphenyliodonium salt. The quantum yield of photopolymerization of methyl methacrylate (7 M) in acetonitrile is 30 with MDEA (0.1 M) and diphenyliodonium (0.05 M). The molecular weight of the isolated polymer is 55,000. In the absence of quantum yield and molecular weight, respectively. Thus, the presence of diphenyliodonium decreases the quantum yield of initiation by approximately 40% and increases the value of k3/kt by a factor of 6. 

Table Z Data of the photopolymerization of methyl methacrylate with ketone-amine initiator systems (IE = ionisation potential, 3k H = quenching constant of ketone triplet state with amine in benzene, AV/At = dilatometric contraction) [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... 

The Inifer technique enables us to fulfil some requirements of polymer architecture even in some radical processes. An amplified form may be applied, the Iniferter variant, where the radical initiator simultaneously acts as a transfer and terminating agent. Otsu et al. used sulphides and disulphides (tetraethylthiuram disulphide, PhSSPh, Ph2S, PhCH2SSCH2Ph) [96] and carbamates (benzyl-A,A-diethyldithiocarbamate, p-xylylene-A,7V-diethyl-dithiocarbamate) [97] in the photopolymerization of methyl methacrylate and styrene, and phenylazotriphenylmethane in the polymerization of methyl methacrylate [98]. Living radical polymerizations yield polymers with defined end groups or the required block copolymers. 

Benzophenone per-esters are apparently highly efficient photoinitiators for the photopolymerization of methyl methacrylate, and Neckers and coworkers have compared the efficiencies of several compounds (1) of this... 

Table 1 Rate of photopolymerization, of methyl methacrylate (bulk) in-...

Representative data [10a] for photopolymerization of methyl methacrylate in aq. AN are given in Table 10. With variation of sensitizer and onium initiator, there is no correlation of (f>m with p. Under similar conditions, the number of average degrees of polymerization, Pn, have been estimated as 260-590 monomer units per chain [113]. 

Shimada, S., Y. Obata, K. Nakagawa, and K. Tabut Photopolymerization of Methyl Methacrylate withMethy-Viologen-So um Dithionite-Carbon Tetrachloride in Aqueous-Organic Two Phase System, Pofy./., 22, 111 (1990). 

Naito et al. have examined the photopolymerization of methyl methacrylate initiated by poly(3-methyl-3-buten-2-one). Again a-cleavage was found to be the dominant initiating step. The photoinitiated polymerization of methyl methacrylate by benzophenone derivatives has been found to depend upon the nature of the substituent, which in turn influences the activity of the semipinacol radical. ... 

Essentially electron-donor substituents retarded polymerization, whereas electron-acceptor substituents accelerated the process. In fact, these workers obtained a good correlation between the Hammett a values of the substituents and the polymerization rate. Remaining with benzophenone, the photopolymerization of 1,3,5-trithiane has been found to be inhibited by amines and also the absence of oxygen,whereas in the hydrogen peroxide-initiated photopolymerization of methyl methacrylate-benzophenone has been found to be a powerful accelerator. In the latter study different solvents were found to have different effects on initiation. In solvents giving low conversions, degradative initiator transfer was found to be a dominant process. 

The photopolymerization of methyl methacrylate using a quinoline-chlorine charge-transfer complex has been investigated. Bulk polymerization was found to follow normal free-radical kinetics, whereas in solution variable monomer exponents were observed depending on the nature of the solvent. The kinetic nonideality in solution was attributed to retardation and initiator termination via degradative chain-transfer involving solvent-modified initiating complexes and chain radicals. 

Similar observations were made in the photopolymerization of methyl methacrylate by a dimethylaniline-nitrobenzene complex. Remaining with methyl methacrylate photopolymerization by A -benzylpyridinium chloride in methylene dichloride is believed to be initiated by a chlorine atom formed from the decomposition of a charge-transfer complex. The presence of the halogen-... 

Koch and A.H. Jones, A photochemical exchange reaction of Michler s ketone, J. Am. Chem. Soc. 92, 7503 (1970) D.I. Schuster and M.D. Goldstein, Photochemistry of ketones in sol ution. XXXVII. Plash photolysis of Michler s ketone in solution. Rate constants for decay and triplet excimer formation, J. Am. Chem. Soc. 95, 986 (1973) V.D. McGinnis and D.M. Dusek, Photopolymerization of methyl methacrylate with the use of 4,4 BIS (diethylamion) benzophenone as the photoinitiator, ACS Polym. Prepr. 15(1), 480 (1974). 

P. Ghosh, P.S. Mitra, Photopolymerization of methyl methacrylate by use of a quinoline-bromine charge transfer complex as the photoinitiator, J. Polym. Sci., Polym. Chem. Ed. 13 (1975) 921-930. 

Valderas et al., also studied the photopolymerization of methyl methacrylate initiated by 2-chlorothioxanthone in the presence of various amines of different structures. Here too, the photoinitiation efficiency of these systems was found to be highly dependent on the structure of the amine. The polymerization rate increases with the amine concentration and reaches a constant value at an amine concentration range of 10—30 mm. At these amine concentrations, aliphatic hydroxyaUcyl amines are more efficient photoinitiators than the corresponding trialkyl-substituted compounds. Dimethylanilines with electron acceptor substituents in the 4-position give higher polymerization rates than electron donor substituted anilines. Their data also show that the singlet and triplet excited states of thioxanthones are efficiently deactivated by the amines. Rate constants correlate well with the oxidation potentials of the amines. The effects of the chemical structure of the amine on the polymerization rates of 2-... 

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,... 

Gosh and Mukherjee reported that monochloroacetic, dichloroacetic and trichloroacetic acids readily initiate photopolymerization of methyl methacrylate at 40 °C in visible light when used in the presence of dimethylaniline. The inhibition period decreases with an increase in the number of chlorine substitution of acetic acid. Addition of benzophenone decreases the induction period. They believe that free-radical initiation is a result of a collapse of the exiplex (acid-dimethylaniline) and an electron transfer from the nitrogen to the carbonyl oxygen of the acid. ... 

The extraordinary photocatalytic performance of AEROXIDE TiOj P 25 in comparison to other nanoscaled titania particles has been published in several papers It is, for example, useful in the degradation of humic acid [71], of phenol and salicylic acid [72], of l,4dichlorobenzene [73], and in the photocatalytic reduction of Hg(II) [74]. It is also used in the oxidation of primary alcohols to aldehydes [75] or in the photopolymerization of methyl methacrylate [76]. Its use in cement can help reduce environmental pollution [77, 78]. A detailed study is reported by Bolte [79]. The results show that crystal size and filling ratio in mass are more important than the modification of the titania. Pyrogenic titania is not only useful in photocatalysis but also in other catalytic applications. 

A combination of benzophenone and 1,3-dioxane is a convenient hydrogen abstraction-type photoinitiator system for the free radical photopolymerization of methyl methacrylate, styrene and other monomers. As an advantage, this system does not require an additional hydrogen donor as other conventional initiators. In a similar way, mixtures of thioxanthone derivatives and fluorenes can be used as visible light absorbing oil- and water-soluble photoinitiators for free radical polymerization of methyl methacrylate, ethyl 2-(2-phosphonoethoxymethyl)acrylate and trimethylolpropane triacrylate. Photopolymerization and laser flash photolysis studies reveal that initiation occurs by intra- and intermolecular hydrogen abstraction by the thioxanthone-like triplet excited state. 

The rates of photopolymerization of methyl methacrylate catalysed by [Fe-(triene)3] +-CCl4 exhibit a complex dependence on the concentrations of the reacting species. At low concentrations of complex the rate is -order in concentration but as [complex] is raised this is reduced to a zero-order dependency, possibly as a result of less efficient free-radical formation. The rate is also proportional to monomer concentration at low concentrations of complex but changes to a f-order dependency at higher concentrations. Addition of CCI4 accelerates the reaction up to a point where the rate does not increase with increased CCI4 concentration. From these findings a radical mechanism is proposed in which the initiation step is... 

Reaction kinetics was monitored for two cases photodimerization of anthracene in the bulk state of binary polymer mixtures, and photopolymerization of methyl methacrylate (MMA) monomer containing a photoreactive polymer as a minor component in the liquid state. 

Chen HT, Gao J, Wang G, Shi SQ, Zhang SB, Cai LP (2004) Effect on temperature on calcium carbonate deposition in situ on bamboo fiber and polymer interfaces. Wood Fiber Sci 46 1-12 Datta C, Basu D, Baneijee AN (2002) Mechanical and dynamical mechanical properties of jute fibers-Novolac-Epoxy composite laminates. J App Polym Sci 85 2800-2807 Garea SA, Nicolescu A, Deleanu C, lovu H (2010) New nanocomposites based on epoxy resins reinforced with modified montmorillonite. Int J Polym Anal Charact 15 497-508 Ghosh P, Mitra PS, Baneijee AN (2003) Photopolymerization of methyl methacrylate with the use of bromine as photoinitiator. J Polym Sci Polym Chem Ed ll(8) 2021-2030 Jia N, Li SM, Ma MG, Sun RC, Zhu L (2011) Green microwave-assisted synthesis of cellulose/ calcium silicate nanocomposites in ionic liquids and recycled ionic liquids. Caibohydr Res 34 2970-2974... 

Mathias et al. studied the photopolymerization of methyl methacrylate on parabolic airplane flights and reported a variation in the molecular weight with g level (34) consistent with a report from a drop tower experiment by Sturm et al. (55). This phenomenon is most likely an effect of mixing caused by composition gradients created during photopolymerization that affects the average rate of initiation throughout the sample. 

CTC of NVP-MA is known to initiate the thermal and photopolymerization of methyl methacrylate. 

Maid, S. Saha, M. K. Palit, S. R. Dye-sensitized photopolymerization of methyl methacrylate in nonaqueous media. Makromol. Chem. 1969, 127, 224-239. 

Very recently, the feasibility of aliphatic tertiary amine like the triethylamine-benzoyl peroxide redox-initiating system in photopolymerization of methyl methacrylate [66] has been reported. In the dilatometric study of methyl methacrylate polymerization at 35°C with various solvents, the initiator exponent was 0.34. The monomer exponent depends on the solvents used. In acetonitrile, pyridine, and bromobenzene, the monomer exponent was 0.5, 0.67, and 1.1, respectively, within the concentration range studied. Benzene and chloroform give first-order dependence of rate on [monomer] and behave as normal (inert) diluents. The activation energy was 3.2 kcal mor. ... 

Like benzoin ethers, benzilketals undergo a-cleavage whereby a benzoyl radical and a dialkoxybenzyl radical is formed. Whereas the benzoyl radicals are, as explained earlier, vigorously reacting with olefinic bonds of vinyl monomers, dialkoxybenzyl radials were found to be of low reactivity. Actually, one of seven dialkoxy benzyl radicals formed is found to be incorporated into the polymer chain during the photopolymerization of methyl methacrylate initiated by DMPA [41]. However, to what extent this portion of dialkoxy benzyl groups is caused by termination rather than initiation remains unclear. 

Benzil and quinones, such as 9,10-phenanthrene quinone and camphor qui-none in combination with hydrogen donors can be used as photoinitiators both in the UV and visible region [120,152,153]. Photopolymerization of methyl methacrylate using benzil was elaborately studied by Hutchinson et al. [120]. They have observed a threefold increase in the polymerization rate when a hydrogen-donating solvent such as THF was used in the system, indicating the importance of hydrogen abstraction. 

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