Monomers for Photopolymerization

Acrylate and methacrylate are used for monomers of photopolymerization. Monofunctional acrylates are shown in Tables 1.3 and 1.4.2-Ethylhexylacrylate (EHA) is polymerized as follows  

2-EthyIhexylacrylate (EHA) CH2= CHCOOCH(C2H5)C4Hc, 1.5 HighTg resistivity for chemicals 

Cetylacrylate CH2= CHCOOC13H33 7.6 Hard adhesive, good coating 

2-Methoxyethy- lacrylate CH2= CHCOOCH2CH2OCH3 1.5 Hydrophobic, low shrinkage, slippery 

3-Methoxybuty- lacrylate CH2= CHCH2CH(CH3)0CH3 1.0 Flexible, sealing, hydrophilic flexibility 

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Acrylic acids and methacrylic acids are mostly applied to polymerize monomers. However, esters of their acids are generally used. Monofunctional monomers are basic monomers for photopolymerization and are used for dilution because of low viscosity. Bifunctional monomers induce crosslinking and hard coating. Polymerization of 1,4-butanediol diacrylate (BDDA) is shown below ... 

After photopolymerization of a certain monomer for a given time, the polymerization mixture was poured into excess precipitant to isolate the polymer, which was then extracted with a solvent to separate the polymer grafted onto the PSG from the homopolymer. 

MIP films, applied to a QCM transducer, have been employed for chiral recognition of the R- and 5-propranolol enantiomers [107]. MIP films were prepared for that purpose by surface grafted photo-radical polymerization. First, a monolayer of 11-mercaptoundecanoic acid was self-assembled on a gold electrode of the quartz resonator. Then, a 2,2 -azobis(2-amidinopropane) hydrochloride initiator (AAPH), was attached to this monolayer. Subsequently, this surface-modified resonator was immersed in an ACN solution containing the MAA functional monomer, enantiomer template and trimethylolpropane trimethacrylate (TRIM) cross-linker. Next, the solution was irradiated with UV light for photopolymerization. The resulting MIP-coated resonator was used for enantioselective determination of the propranolol enantiomers under the batch [107] conditions and the FIA [107] conditions with an aqueous-ACN mixed solvent solution as the carrier. The MIP-QCM chemosensor was enantioselective to 5-propranolol at concentrations exceeding 0.38 mM [107]. 

Polymer and copolymer. Polymer and copolymer were prepared in our laboratory for strict control of purity, branching content and molecular weight. All monomers and solvents were carefully purified. PVC samples were prepared as powders in bulk using free radical photoinitiation with either AIBN or uranyl nitrate as initiators. The AIBN/UV initiation was used for photopolymerization at temperatures of 50°, 25°, and 0°C. 

In course of subsequent work Bubeck, Tieke, and Wegner discovered that the action spectrum for photopolymerization of undoped diacetylene multilayers extends into the visible provided some polymer formed in course of previous UV-irradiation is present. Since obviously excitation of the polymer can sensitize the reaction this effect has been termed self-sensitization. Checking the absorption spectrum of the polymer produced via self-sensitization assured that the final product is identical with the product obtained under UV excitation of the monomer. Later work by Braunschweig and Bassler demonstrated, that the effect is not confined to multilayer systems but is also present in partially polymerized single crystalline TS-6, albeit with lower efficiency. Interestingly, the action spectrum of self-sensitization follows the action spectrum for excitation of an electron from the valence band of the polymer backbone to the conduction band rather than the excitonic absorption spectrum of the polymer which is the dominant spectral feature in the visible (see Fig. 21). The quantum yield is independent of the electric field, whereas in a onedimensional system the yield of free carriers, determined by thermal dissociation of optically produced, weakly bound geminate electron-hole pairs, is an linear function of an applied electric field 29.30,32,129) Apparently, the sensitizing action does not... 

Though the quantum yield for photopolymerization with UV light is high at low polymer conversions, it rapidly decreases as the polymer concentration increases [2). The limiting yield for UV polymerization in 4BCMU is about 35%. It is believed that this effect has its origin in quenching of the monomer excited states by the polymer chains, i.e., the monomer excited states created on irradi-... 

Equation (6.81) indicates that for photopolymerizations Rp is first order in [M], I Order in light intensity and 1-order in [A] for the case where there is negligible attenuation of the light intensity in traversing the reaction vessel. When the photoexcitation involves monomer, i.e., A is M, Eq. (6.81) becomes... 

A vinyl monomer is photopolymerized in two experiments in which only the temperature is varied. In these experiments, the time to convert 20% of the original charge of monomer to polymer is found to be 30 min at 60°C and 27 min at 70°C. However, when an organic peroxide is used as the initiator, the corresponding times for 20% conversion are 62 min at 60°C and 29 min at 70° C. What is the activation energy for the dissociation of the organic peroxide ... 

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]. 

Other monomers (for example acrylamide, styrene, vinylpyrrolidone, vinylcar-bazole, vinyl ether, allyl ether, etc.) can be likely studied by carefully selecting other initiating radicals. Cross-polymerization might also be investigated, for example, the addition of TEA-M to vinyl ether since TEA does not react with vinyl ether. The results obtained with this procedure can also be extended to the behavior of different acrylate structures in photopolymerization experiments carried out in bulk. 

Because of releasing very stable cations upon irradiation, phosphonium salts containing pyrenylmethyl groups are excellent initiators for photopolymerization of convenient monomers such as epoxides and vinyl monomers [35,39]. 

The silicas Ila-d were used for photopolymerization of nonofunctional monomers which were applied as undiluted liquids or as ethanolic solutions. Several monomers were tested first without a solvent on their ability to polymerize. 

Uses Monomer for flexible substrates, photopolymeric printing plates, and no-wax vinyl tile coatings... 

Chem. Descrip. Oligo (2-hydro) -2-methyl-1-4 (1-methylvinyl) phenyl propanone and 2-hydroxy-2-methyl-1-phenyl-1-propanone (polymeric) Uses Photoinitiator for photopolymerization of UV-curable systems based on acrylic unsat. oligomers and monomers, adhesives, coatings, electronics, inks, fiber optics, pkg. 

Figures Illustration of common shear rheology measurements for photopolymerization reactions, (a) Evolution of dynamic viscosity with exposure time for HEMA, HEMA MMA, and MMA monomers photo-polymerized with Darocur 1173. The gel point is defined as the time at which viscosity goes to infinity, (b) Typical profile for modulus change in photopolymerizable gels. G and G" denoting shear (storage) and loss (viscous) moduli. Gel point is defined as when G -G".

Thus, research on ways to refine the use of polymer stationary phases within the pGC channel design also continues. Examples include using UV photopolymerization of gas-phase monomers for thin-film depositimi [8] and plasma polymerization [9]. 

Hsieh MD, Zellers ET (2002) In situ UV-photopolymerization of gas-phase monomers for microanalytical system applications. Sens Actuators B 82(2-3) 287-296... 

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