Photoinitiated polymerization of methyl methacrylate

In the benzophenone-photoinitiated polymerization of methyl methacrylate, interpretation (i) would tend to increase the order of reaction with respect to monomer concentration, whereas interpretation (ii) would tend to decrease this, assuming that the species formed as the result of quenching initiated polymerization less efficiently than the solvent-derived radicals. The data of Block et al. (46) give a value of 0.84 for the order in monomer, and it could be argued that this is significantly lower than the value of unity predicted by the suggested... 

Solvent effectiveness in the benzophenone-photoinitiated polymerization of methyl methacrylate was in the order tetrahydrofuran > isopropanol > toluene > benzene (46). In the case of TCMB, isopropanol gaw slightly higher polymerization rates than tetrahydrofuran, but both wore again considerably more effective than toluene and benzene. As might be expected, monomers which thonselves contain ether grouj , e.g. diethylene glycol diacrylate (7), do not require addition of a separate hydrogen-donor solvent for efficient photoinitiation by benzophenone. 

Benzil has frequently been used as a means of generating free radicals in polymerization systems subjected to ultra-violet irradiation 11, 16, 56—58). In studies of the benzil-photoinitiated polymerizations of methyl methacrylate, and vinyl acetate, Melville (16) assumed that initiation was brought about by fragmentation of photoexcited benzil into two benzoyl radicals. However a survey of the photochemistry of benzil 34) indicates that such a cleavage does not in fact take place in solution studies of the products formed on irradiation of benzil in cyclohexane (59), cumene and isopropanol (60) can be rationalised on the basis of initial hydrogen abstraction from solvent by photoexcit i benzil, e.g. 

Table 23. Photoinitiated polymerization of methyl methacrylate (MMA) in benzene solution, using polymeric photoinitiators based on benzoin methyl ether and benzoin moieties (BE) as well as their low-molecular-weight analogues [111]...

Gosh and Gosh [105] studied photoinitiated polymerization of methyl methacrylate initiated by the BP-TV,A-dimethylaniline couple, and Clarke and Shanks [106] tested the influence of a variety of amines on benzophenone-initiated polymerization. That amino radicals resulted during the initiation the polymerization by benzophenone-tertiary aromatic amines was shown by Li through the use of ESR and spin-trapping methods [107]. It was shown that the rate of photoinitiated polymerization depends on the structure of the amine. More recently [108] benzophenone-tertiary aromatic amines were studied as initiators of the free-radical polymerization of polyol acrylates. Illustrative kinetic curves recorded during photoinitiated polymerization of TMPTA are shown in Figure 23. 

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. ... 

Photoinitiated polymerization of methyl methacrylate (1.0 M in benzene) is carried out using a photosensitizer and 3130 A light from a mercury lamp. If the quantum yield for radical production in this system is 0.50 and light is absorbed by the system at the rate of 10 ergs/L-s, calculate the rate of initiation. 

For Lewis acid promoted living polymerization of MMA with (TPP)AlMe (1,X= Me) as initiator, a photoinitiation prior to the addition of the Lewis acid is required. This is because (1) 1 (X=Me) without irradiation does not have the ability to initiate the polymerization even in the presence of Lewis acid, and (2) all-at-once polymerization by direct irradiation of a mixture of MMA, 1 (X=Me), and the Lewis acid results in the formation of a relatively broad MWD PMMA with Mn much higher than expected. In this sense, the procedure using 1 (X= Me) as initiator is not convenient for practical application. In this section, we report on aluminum porphyrins with various axial ligands which were tested as initiators in order to realize a more convenient, one-shot high-speed living polymerization of methyl methacrylate with no need for irradiation with visible light. 

Phenyl phenacyl sulphide has also been reported to be a good photoinitiator for the polymerization of methyl methacrylate, acrylonitrile, styrene, and vinyl acetate (30). 

Block, Ledwith and Taylor (46) have reported the results of a detailed investigation into the efficiencies of benzof enone, 3,3, 4,4 -benzo-phenone tetracarboxylic dianhydride (BTDA) and 3,3, 4,4 -tetramethoxy-carbonyl benzophenone (TMCB) as photoinitiators for the polymerization of methyl methacrylate in tetrahydrofuran at C in vacuo. 

A comprehensive study of the free radical polymerization of methyl methacrylate (MMA) photoinitiated by anthraquinone and 2-tert-butyl anthraquinone in tetrahydrofuran has been completed by Ledwith, Ndaalio and Taylor (78). 2-tert-butyl anthraquinone is frequently used in applications (72—76) on account its greater solubility and com-... 

In the photopolymerization of methacrylamide by benzoin methyl ether, chain-transfer to monomer has been found to be important, and benzalde-hyde is reported to be an inefficient photoinitiator of methyl methacrylate polymerization unless benzophenone and triethylamine are present. Acetophenone has been found to sensitize the cycloaddition of maleic anhydride to 7-oxabicyclo[2.2.1]heptan-5-one-2,3-dicarboxylic anhydride, , a-hydroxy-acetophenone derivatives have been found to be non-yellowing initiators, and h.p.l.c. has been used to determine residual carbonyl photoinitiators in u.v.-cured resins. In the emulsion-polymerization of methyl methacrylate using an aromatic ketone and a continuous or intermittent laser, the former conditions were found to be similar to those under continuous u.v. irradiation. The dependence of the polymerization rate and average chain-length on the absorbance of the initiator used in the photoinitiated polymerization of vinyl monomers has been studied. Interestingly, irrespective of all conditions, maximum conversion is observed when initiator absorbance is 2.51. "... 

Anthraquinone (AQ)-triethylamine (TEA), a photoinitiating system for the polymerization of methyl methacrylate (MMA) [133], elearly functions by electron... 

Dainton and Tordoff (9) showed that in the case of acrylamide Fe+ OH is a significant terminator. I am not, however, convinced of the validity of their suggested extension of this mechanism to other vinyl monomers, and similar generalizations, particularly in view of the fact that under otherwise identical conditions in experiments concerning the oxidation of benzoic acid (4) a doubled maximum yield of ferrous ion formation was determined by straightforward analytical methods, indicating that in the latter case, but not in the former, Fe+ OH must be considered as a terminator. This is quite independent of the quantitative estimate of the Fe+30H primary yield, which has become controversial. It is, however, feasible that Fe+ Br did not act as photoinitiator of the polymerization of methyl methacrylate or acrylonitrile because of eflficient termination with Fe+ Bir, which would not be unexpected. 

Bulk semiconductors and powders have been used as initiators for radical polymerization reactions [140-144], Recently the study has been extended to semiconductor nanoclusters [145-147]. It was found that polymerization of methyl methacrylate occurs readily using ZnO nanoclusters. Under the same experimental conditions, no polymerization occurred with bulk ZnO particles as photoinitiators [145], In a survey study, several semiconductor nanoclusters such as CdS and Ti02, in addition to ZnO, were found to be effective photoinitiators for a wide variety of polymers [146], In all cases nanoclusters are more effective than bulk semiconductor particles. A comparison of the quantum yields for polymerization of methyl methacrylate for different nanoclusters revealed that Ti02 < ZnO < CdS [146]. This trend is parallel with the reduction potential of the conduction band electron. The mechanism of polymerization is believed to be via anionic initiation, followed by a free-radical propagation step. 

In spite of the large number of available photoinitiators [4], the search for new initiators is ongoing. For example, S-(4-benzoyl)phenylthiobenzoate, BpSBz, has been found to be a type I photoinitiator. Upon exposure to light it is cleaved into free radicals (quantum yield 0.45), which initiate the polymerization of methyl methacrylate. In contrast, BpOBz (see Chart 10.1) is not cleaved. It forms a long-lived triplet state rather than free radicals [43]. 

Inorganic materials such as titanium dioxide, Ti02, and cadmium sulfide, CdS, can initiate the polymerization of unsaturated compounds upon exposure to light [49-51]. For the photoinitiation of the polymerization of methyl methacrylate by nanosized titanium dioxide [49, 50], the mechanism presented in Scheme 10.8 has been proposed. Accordingly, electrons released upon absorption of light by the Ti02 particles are trapped at the hydrated surface of the particles by groups. formed in this way can react with molecular... 

Strongly redshifted fluorescence, as the solvent polarity was increased, demonstrated the formation of an intramolecular charge transfer state. Compounds under study were used as fluorescence probes for monitoring the kinetics of thermally initiated polymerization of methyl methacrylate and photoinitiated polymerization of 2-ethyl-2-(hydroxymethyl)propane-l,3-diol triacrylate. 

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 aqueous polymerization of methyl methacrylate initiated by the potassium trioxalate cobaltate (II) complex was studied by Guha and Palit [190]. At a relatively higher concentration (>0.001 mol L ), this compound can initiate aqueous polymerization of methyl methacrylate in the dark at room temperature. The complex is highly photosensitive, which can photoinitiate polymerization. A detailed end-group analysis of the obtained polymers indicated that carboxyl and hydroxyl radicals, which are from the decomposition of the photoexcited complex, are the initiating species. 

Quarternary salts in combination with benzoyl peroxide are known to induce vinyl polymerization in emulsion systems [79,80]. Quartemary salts are also potential photoinitiators for vinyl polymerization [81]. The use of quarternary salts in combination with peroxides as redox initiators for suspension polymerization of styrene [82] and polymerization of methyl methacrylate [83,84] in bulk or in solution have been explored. 

Ajayaghosh A, Francis R (1999) A xanthate-derived photoinitiator that recognizes and controls the free radical polymerization pathways of methyl methacrylate and styrene. J Am Chem Soc 121 6599-6606... 

Kinetics and Mechanism of Methyl Methacrylate Polymerization Photoinitiated by Benzophenones in Tetrahydrofuran... 

New photoreactive polymers with dimethylmaleimide side groups have been prepared, "" and co-polymers of methyl methacrylate with oligourethanes have tensile properties superior to those of the separate homopolymer systems."" New monomers have been prepared for fire-retardant u.v.-curable polymers " and trimethylolpropane has been photopolymerized in the vapour phase. Diphenylsulphoniumbis(methoxycarbonyl)methylide photoinitiates the polymerization of styrene and methyl methacrylate through the formation of... 

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