Irradiation photopolymerization

Vinyl acrylate (VA) is an intriguing compound capable of self-initiation under UV irradiation. Photopolymerization of VA proceeds faster when PI is added, with other conditions being the same. The question is which double bond is attacked by r of PI (Scheme 12.9). 

General Electric Co.) were added to the acrylic and epoxy monomers, respectively, to initiate photopolymerization. The acrylic monomers that polymerized by a free-radical mechanism were irradiated under nitrogen. The output of the lamp measured at the substrate was about 4 mW/cm2 at 260 nm and about 11 mW/cm2 at 310 nm. 

Photopolymerizations of the bis-pyrimidine derivatives were carried out in solid film by irradiation with UV light from a spectroirradiator. The rate of the photopolymerization was found to depend on the wavelength of light. The highest reactivity was observed at 300 nm (Figure 7a), while the highest reactivity for photoreversal of the photodimer was obtained by irradiation at 240 nm (Figure 7b). The polymers... 

Laterally-defined heterogeneous polymer surfaces can be created by using a homogeneous layer of an azo initiator. UV irradiation through a mask in the presence of monomer leads to the locally confined photopolymerization [234]. A second polymerization using the remaining initiators results in patterned surfaces composed of two types of polymer brushes [238]. However, the lateral resolution of obtainable patterns is hmited by the irradiation used and type of mask (in this case polymer brush patterns of 260 tm spaced by -40 pm were formed). 

Conventionally, solutions of acrylamide or other acrylic monomers, or mixtures of them, can be photopolymerized onto flat glass surfaces which have previously been derivatized with acrylic groups to promote covalent and robust binding of the gel (e.g. by reaction with 3-(triethoxysilylpropyl)acryla-mide) [59]. Irradiation of the substrate occurs through a mask, so that poly-... 

The PLP-SEC method, like the rotating sector method, involves a non-steady-state photopolymerization [Beuermann, 2002 Beuermann and Buback, 2002 Komherr et al., 2003 Nikitin et al., 2002], Under pulsed laser irradiation, primary radicals are formed in very short times ( 10 ns pulse width) compared to the cycle time ( 1 s). The laser pulse width is also very short compared to both the lifetimes of propagating radicals and the times for conversion of primary radicals to propagating radicals. The PLP-SEC method for measuring kp requires that reaction conditions be chosen so that no significant chain transfer is present. The first laser pulse generates an almost instantaneous burst of primary radicals at high... 

Quantitative aspects of photopolymerization have been described in Sec. 3-4c. There are some differences between radical and cationic photopolymerizations. The dependence of Rp on light intensify is half-order for radical polymerization, but first-order for cationic polymerization. Radical photopolymerizations stop immediately on cessation of irradiation. Most cationic photopolymerizations, once initiated, continue in the absence of light because most of the reaction systems chosen are living polymerizations (Sec. 5-2g). 

Convincing evidence for phase separation was obtained from the photopolymerization behavior of 6 in the mixed 6/DSPE monolayer films. Photopolymerization of diacetylenes is a topotactic process which requires the proper alignment of the 1,3-diyne moieties [35]. Thus diacetylenes typically polymerize rapidly in the solid state but not in solution. Polymerization is triggered by ultraviolet irradiation and proceeds via a 1,4-addition mechanism yielding a conjugated ene-yne backbone (Fig. 5). The reaction can be followed by the growth of the visible absorption band of the polymer. 

Although precise photopolymerization conditions were not supplied by the author, samples were irradiate 30 seconds using a high-pressure mercury lamp having a wavelength of between 300 and 400 nm. Samples were additized with 0.1 wt%... 

It is important to note that values are of the same order of magnitude whether conventional UV or laser radiation were used (Table I). This result is in contrast with the recent work of Sadhir et al. (7) on the photopolymerization of maleic anhydride and styrene, induced by the 363.8 nm emission of an argon ion laser. That work showed to be the laser initiation 1000 times more energy efficient than the UV-induced polymerization. This discrepancy may arise from two factors (i) the lower light-intensity used in the laser irradiation that should favor chain propagation and (ii) differences in the way of comparing the... 

At present, it is common knowledge that not only the photoreactivity, but also the stereochemistry, of the photoproduct is predictable from crystallographic information of starting olefin substrates. This ability of olefinic crystals to dimerize has been widely applied to the topochemical photocycloaddition polymerization of conjugated diolefinic compounds, so called "four-center type photopolymerizations" (7,8). All the photopolymerizable diolefin crystals are related to the center of symmetry mode (centrosymmetric -type crystal) and thus give polymers having cyclobutanes with a 1,3-trans configuration in the main chain on irradiation. 

Table 4. Additive effects on photopolymerization of VCZ-NB system without sensitizer at 30 C, [VCZ] = 0.25 M. Irradiation by a 300 W high-pressure mercury lamp from...

Oster [174] proposed the second hypothesis to explain his results on the photopolymerization of acrylonitrile in aqueous solution, buffered at pH 7.0, and sensitized by xanthene dyes and riboflavin using ascorbic acid as the reducing agent. Whereas the monomer is efficiently polymerized when the solution is illuminated in the presence of oxygen, irradiation in its absence leads to photoreduction of the dye to its leuco form but no polymer is formed. Therefore, the author suggests that the leuco dye reacts with atmospheric... 

---