UV photopolymerization

It has been known for some time that UV photopolymerization of multifunctional monomers does not obey the classical rate expression, Rp proportional to I0 5, but follows an approximately first-order relationship [196,197]. These results have been explained by postulating that, in these viscous monomers, radical occlusion competes with bimolecular termination. 

The quantum yield of photopolymerization, as well as the kinetic chain length ( p/ i), decrease with the square root of the absorbed light intensity. For an absorbed light intensity of 1.06 xlO-4 einsteins/1 x s and borate concentration of 10 mM the photopolymerization quantum yield is 1420. The quantum yield for radical generation is 0.067 [274], giving a kinetic chain length of 2.1 x 104, which compares favorably with the value of 2.9 x 104 reported for the UV photopolymerization of epoxy diacrylate/TMPTA in the presence of air [282]. 

An alternative to sintering frits, which deserves mention here, is to form frits via UV photopolymerization of a glycidyl methacrylate and trimethylolpropane trimethacrylate solution (UV radiation, 365 nm for 1 hour) [135]. The photopolymerization process is similar to that used in the fabrication of monolithic columns (Chapters 5 and 6). Frits fabricated with this method have shown to be reproducible since there is no sintering of packing material, weakening of the capillary column by removal of the polyimide coating and/or alteration of the stationary phase at the frit are avoided. 

Rg. 12. Time dependent absorption of reaction intermediates A to D observed upon UV-photopolymerization of TS-6 crystals at 270 K. AOD is the change in optical density of the sample (from Ref. )... 

Fig. 3. Optical absorption spectra of a diacetylene crystal (TS-6) at about room temperature. The optical density is proportional to the absorption coefficient. The absorption in the visible spectral region is due to the polymer filaments. UV photopolymerization has been performed in steps using the same photon numbers, respectively...

Fig. 5. Generation of the intermediates A to E obtained in the UV-photopolymerization reaction at 10 K. The intensity of the absorption lines is a function of the absorbed photons (proportional to the irradiation time). The calculated dependencies are fitted to the experimental points...

Figure 22 includes the temperature dependent polymerization rates (1), (2) and (3). The thermal polymerization kinetics (1), they — (2), and the UV photopolymerization kinetics (3) have been investigated by the method of diffuse reflection spectroscopy and other methods The activation energy of the thermal reactions (2) and (3) following the photoinduced dimerization processes, (150 + 30) meV, is appreciable lower than those of the dimer DR intermediates. However, the processes which dominate the polymerization reaction are determined not by the short diradicals with n 6 but by the long chains with n 7, which all have a carbenoid DC or AC structure. The discrepancy of the activation energies therefore may be due to the different reactivities of the diradical and carbenoid chain ends. The activation energies of the thermal addition reactions of the AC and DC intermediates at low temperatures have not been determined and therefore a direct comparison with those of the diradicals is not possible. 

As was indicated in Section 3.3, an issue to be addressed before glucose or other biosensors is a commercially practical sensor fabrication. An easier and simpler sensor fabrication method was recently investigated using ferrocene modified redox polymer hydrogels. Sirkar and Pishko reported amperometric biosensors based on oxidoreductase immobilization in UV-photopolymerized... 

Fig. 23 Schematic illustration of the preparation of chemically crosslinked polyrotaxane hydrogels through crosslinking the ends of the threading polymers via UV photopolymerization [97]...

Sample Preparation Langmuir-Blodgett, Langmuir Schaefer Transfer, and UV Photopolymerization... 

Using a QCM, Josse et al. [27] have determined the storage and loss modulus of a commercially available UV-curable epoxy resin (SU-8-2002). An in-line monitor of the UV photopolymerization of 2-hydroxyethyl methacrylate with a photoinitiator of 1-chloroanthraquinone was demonstrated by Kim et al. [39]. 

Heterochain polymers of the type -(M-X) - contain polar M-X bonds (for reviews see [1,2,12-15]). Such polymers are often prepared by polycondensation of a bifimctional metal halide (M = B, Si, Ge, Sn, Pb, Sb, Ni, Pd, Pt, Ti, Hf) with a bifunctional Lewis base such as a diol, diamine, dihydrazine, dihydrazide, dioxime, diamideoxime, dithiol, diacetylene (Eq. 7-2). Another possibilitiy is the polyaddition of a bifunctional metal hydride to bifunctional alkenes (Eq. 7-3). Mn and mg containing poly(p-xylylenes) of the composition -(-CH2-C6H4-CH2-M-) - were produced by solid-state UV-photopolymerization of a cocondensated mixture of p-xylylene with Mn or mg at 80 K [16]. Prolonged storage of the polymers at ambient temperature under vacuum led to gradual decomposition. 

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... 

Wang, H., Feng, Y, An, B., Zhang, W, Sun, M., Fang, Z. et al (2012) Fabrication of PU/PEGMA crosslinked hybrid scaffolds by in situ UV photopolymerization favoring human endothelial cells... 

Finally, it is also worth noting that the polymerization of FA to PFA can be achieved using UV radiation. The UV-photopolymerization of FA has been investigated for its potential appUcation as a resin for stereolithography [69, 70]. As with conventional RIM, UV-RIM requires low viscosity precursors, and hence FA, which is a clear Uquid of low viscosity at room temperature, lends itself to this appUcation. 

In additional studies the quantum yield 4> of the UV-photopolymerization was determined. single photon initiates the formation of a whole polymer diain. 

Ethyl acrylate Tetraethylene glycol Benzoin uv photopolymerization Thermal polymerization with 1... 

Styrene Divinyl benzene Benzoin uv photopolymerization Usually requires 1-3 days. 1-3... 

Methyl TEGDM Benzoin uv photopolymerization Isomeric with ethyl acrylate. 1... 

LIA 99b] Liang L., Feng X., Peurrung L. et al, Temperature-sensitive membranes prepared by UV photopolymerization of A/ -isopropylaciylamide on a surface of porous hydrophilic polypropylene membranes . Journal of Membrane Science, vol. 162, pp. 235-246,1999. 

Figure 9.8 UV photopolymerization of TS6 The monomer crystal is irradiated with an UV-flash. The dimer is formed from the monomer by a photoreaction, then a series of thermally activated monomer addition reactions leads via die diradicals (DR) and dicarbenes (DC) to the polymer.

By means of UV photopolymerization high-efficiency holographic grating on diacetylene crystals can be recorded, as was first shown by Richter et al. [55, 56]. Utilizing a fre-... 

Scherzer T, Mehnert R, Lucht H. On-line monitoring of the acrylate conversion in UV photopolymerization by near-infrared reflection spectroscopy. Macromol Symp 2004 205 151-162. 

Fig. 5 Hydrogel patterns produced (dry state) by UV photopolymerization (50 mW/cm ) (Paschew 2006). The right-hand picture is an enlarged image of the original one left side)...

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