Visible Light Polymerizations

Figure 22. Visible-light polymerization of acrylic formulation with DBIF and tetramethylammo-nium tetraorganoborates as electron donors. Data from Ref, [89].

Explosive, flammable and toxic liquid. Should be stored and used in closed systems whenever possible. Work areas should be adequately ventilated, and should be free from open lights, flames, and equipment that is not explosion-proof. Handle in hood. May polymerize spontaneously, particularly in the absence of oxygen or on exposure to visible light. Polymerizes violently io the presence of concentrated alkali. On standing may slowly develop a yellow color particularly after excessive exposure to light, hp 77.3 bpsoo 64.7° bp2b, 45.5° bp--, 23,6° bp,<, 8.7°. mp -83.55°. d 0.8060 df 0.8004. ng 1.3888. Flash pt. open cup 32°F (0°C). Explosive mixtures in air at 25° 3.05% low... 

W. Schroeder, S.V. Asmussen, M. Sangermano, C.I. VaUo, Visible light polymerization of epoxy monomers using iodonium salt with camphotquinone/ethyl-4-dimethyl amino-benzoate, Poym. Int. 62 (2013) 1368-1376. 

Photopolymerization. In many cases polymerization is initiated by ittadiation of a sensitizer with ultraviolet or visible light. The excited state of the sensitizer may dissociate directiy to form active free radicals, or it may first undergo a bimoleculat electron-transfer reaction, the products of which initiate polymerization (14). TriphenylaLkylborate salts of polymethines such as (23) ate photoinitiators of free-radical polymerization. The sensitivity of these salts throughout the entire visible spectral region is the result of an intra-ion pair electron-transfer reaction (101). 

This facile reaction involves a modest change in the absorption of visible light, largely because of the visible absorption band of <7 -azobenzene [1080-16-6] having a larger extinction coefficient than azobenzene [17082-12-1]. Several studies have examined the physical property changes that occur upon photolysis of polymeric systems in which the azobenzene stmcture is part of the polymer backbone (17). 

Dentures require accurate fit, reasonable chewing efficiency, and lifelike appearance (189). The chewing efficiency of artificial dentures is one-sixth that of natural dentition (190). AcryHc resins are generally used as powder/Hquid formulations for denture base, bone cement, and related appHcations. Polymerization is achieved thermally using initiators photochemicaHy using photoactive chemicals and either uv or visible light irradiation and at ambient temperatures using initiator/activator systems. 

Radiation curing of epoxies with cationic initiators is well known [20—28]. UV-visible light has been the predominant radiation source the process has been limited to thin coatings due to the low penetration of the visible-UV light [22,23], Thermal and mechanical properties of these materials are low and the curing is incomplete. Several studies have shown that commercially available epoxies with various cationic initiators can be polymerized with EB curing [20,29-34]. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Attacks copper and copper alloys these metals should not be used. Penetrates leather, so contaminated leather shoes and gloves should be destroyed. Attacks aluminum in high concentrations Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization May occur spontaneously in absence of oxygen or on exposure to visible light or excessive heat, violently in the presence of alkali. Pure ACN is subject to polymerization with rapid pressure development. The commercial product is inhibited and not subject to this reaction Inhibitor of Polymerization Methylhydroquinone (35 - 45 ppm). 

Photopolymerization of MMA was also carried out in the presence of visible light (440 nm) using /3-PCPY as the photoinitiator at 30°C [20]. The initiator and monomer exponent values were calculated as 0.5 and 1.0, respectively, showing ideal kinetics. An average value of kp /kt was 4.07 x 10 L-mol -s . Kinetic data and ESR studies indicated that the overall polymerization takes place by a radical mechanism via triplet carbene formation, which acts as the sources of the initiating radical. 

Methyl Methacrylate CH2=C(CH3)COOCH3 Impure Methyl-Methacrylate Vap in Air 2.1 to 12.5% > Ambient > 110 Inhibitor-Hydroquinone or Methyl Ether of Hydro-quinone. Shield from light avoid sparks. Store in cool place 13.3-13.8 421 Self-polymerizing initiated by visible light at 20 to 40°... 

Toshima, N., Takahashi, T., and Hirai, H., Polymerized micelle-protected platinum clusters-preparation and application to catalyst for visible light-induced hydrogen generation, J. Macromol. Sci. -Chem., A25, 669,1988. 

Figure 2 The rate of polymerization of MSA as a function of time initiated with (a) 1.0 wt% DMPA and 60 mW/cm ultraviolet light, (b) 0.05 wt% DMPA and 60 mW/cm ultraviolet light, and (c) 1.0 wt% camphorquinone, 1.0 wt% triethanolamine and 25 mW/cm visible light.

Incineration or heating to decomposition releases toxic nitrogen oxides (Sittig, 1985) and cyanides (Lewis, 1990). Wet oxidation of acrylonitrile at 320 °C yielded formic and acetic acids (Randall and Knopp, 1980). Polymerizes readily in the absence of oxygen or on exposure to visible light (Windholz et al., 1983). If acrylonitrile is not inhibited with methylhydroquinone, it may polymerize spontaneously or when heated in the presence of alkali (NIOSH, 1997). 

Another very important visible light-initiated reaction of alkyl aluminum porphyrins is their 1,4-addition to alkyl methacrylates to produce ester enolate species [Eq. (4)]. This enolate then acts as the active species in the subsequent polymerization of the acrylate monomer. For example, Al(TPP)Me acts as a photocatalyst to produce polymethylmethacrylate with a narrow molecular weight distribution in a living polymerization process [Eq. (4)]. Visible light is essential for both the initiation step (addition of methylmethacrylate to Al(TPP)Me) and the propagation... 

Photochemical or photoinitiated polymerizations occur when radicals are produced by ultraviolet and visible light irradiation of a reaction system [Oster and Yang, 1968 Pappas, 1988]. In general, light absorption results in radical production by either of two pathways ... 

Tricot YM, Emeren A, Fendler JH (1985) In situ Generation of catalyst-coated CdS particles in polymerized and unpolymerized surfactant vesicles and their utilization for efficient visible-light-induced hydrogen-production. J Phys Chem 89 4721-4726... 

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