Photo-sensitized polymerization

The fabrication of a conducting polymer pattern is considered to be one of the most important subjects in the field of molecular electronic devices. A novel photo-sensitized polymerization of pyrrole was investigated, in order to form fine conducting polymer patterns... 

Today, flexographic presses and letterpress presses, for newspaper printing, use t q)es made of photo-sensitive polymeric materials that can be formed directly from a light image. The polymeric cylinder when properly developed presents raised areas that reproduce the image to be printed. 

DBPOX, a low temperature initiator, decomposes easily at room temperature into t-butoxy radicals and carbon dioxide (Eq. (1)) The t-butoxy radical undergoes both addition to the monomer (Eq. (2)) and hydrogen-abstraction from the N-methyl group (Eq. (3)) Radicals 1 and II attack the monomer and propagate yielding poly(NMAAm) radicals (Eq. (4)). The stable poly(NMAAm) radic was similarly formed in the photo-sensitized polymerization with azo-bis-isobutyronitrile(AIBN) or di-tert-butyl peroxide(DBPO). In the latter system, the concentration of living radical III reached 1 x mol/1... 

Acrylamide (AAm) and methacrylamide (MAm) were likewise converted into the living propagating radicals V and VI by their photo-sensitized polymerization with DBPO in dioxane ESR spectra of polymer radicals V and VI are shown as (a) and... 

Figure 3 shows a transmission electron micrograph of poly(NMMAm) in a poly(p-methylstyrene)(p-MeSt) matrix. The sample was prepared by an AIBN-initiated polymerization of a p-MeSt solution containing dispersed poly(NMMAm). Poly-(NMMAm) formed in a photo-sensitized polymerization of NMMAm with DBPO in benzene was used for this electron microscopic examination. 

As mentioned above, some amide monomers are easily converted into their living propagating radicals when they undergo photo-sensitized polymerization with DBPO in benzene or dioxane at room temperature. Therefore, it is of interest to examine the post-effect in the photo-sensitized polymerization of the amide monomers. Fig. 4 shows the results obtained in the post-polymerizations of AAm in dioxane and NMMAm in benzene at room temperature . As it can be seen from the figure, a small post-effect was observed in the AAm polymerization. On the other hand, no... 

Photospeeds reported were similar to those encountered in photo-reducible dye sensitized polymerizations, and similar photopolymer functionality was demonstrated (e.g., washout development). Reductive decomposition of diazonium salts is well known to produce free radicals (98). 

This review has demonstrated that a wide variety of organic and organometallic electron donors and a smaller number of electron acceptors can function as coinitiators for the photo-induced polymerization of monomers using photoreducible or photooxidizable dyes as absorbers of incident light. These compositions can be used for a number of applications in the printing, graphics arts, and electronics industries where sensitivity to visible wavelengths is necessary. 

Irradiation by Ultra-Violet or Visible Light. Systems of this nature comprise materials such as acrylic resins in which a photo-sensitizer (for example, benzophenone) is incorporated. On exposure to ultra-violet radiation the photo-sensitizer dissociates into free radicals which then catalyse polymerization of the acrylic material. The reaction is controllable and takes place within a few seconds the ultra-violet radiation may be directed and focused so as to obtain cure precisely where needed. Products like these are used to retain coatings, wiring, and other components in the assembly of electronic goods. 

Kinetics and Mechanism. Practical applications of onium salt photo-initiated polymerization generally require use of spectral sensitizers. Under conditions of electron transfer mediated sensitization, the initiating cation, R+, thus derives from the sensitizer, not the onium salt (see above), that is, a Lewis, rather than a Bronsted, acid functions as the polymerization catalyst. As a result overall polymerization quantum yields are very dependent on sensitizer [93,166]. 

F. Kasapoglu and Y. Yagci, Photo sensitized cationic polymerization of cyclohexene oxide using a phenacylanihnium salt. Macromol. Rapid Commun 2002,23(9), 567-570. 

J.V. Crivello, et al., Advances in the design of photoinitiators, photo-sensitizers and monomers for photoinitiated cationic polymerization. Macromol. Symp. 2004, 215, 165-177. 

Problem 6.9 Methyl methacrylate is polymerized in 10% w/v solution using a photo-sensitizer and 3130 A light from a mercury arc lamp. Direct measurement by actinometry shows that light is absorbed by the system at the rate of 1.2x10 ergs/L-s. If for the system is 0.60, calculate (a) the rate of initiation and (b) the rate of polymerization, [kp/kj at 60°C= 0.102 mol i/ 5-1/2 j... 

After the oxide layer has been grown, a thin layer of photoresist is applied to the wafer s surface. The photoresist is a radiation-sensitive polymeric solution. It contains a complex mixture of photo-sensitive molecules and solvents. The layer of photoresist must be very thin, of the order of two microns, and spin coating is a process that is used to obtain a uniform layer... 

By a technique which interposed a rotating sector between a source of UV radiation and a dilatometer bearing a monomer, variations in the rotational speed of the sector and size of the opening, controlled bursts of radiation strike the monomer and induce polymerization. From the frequency of exposure and the effect on the polymerization many of the kinetic constants were evaluated. In this connection it should be noted that vinyl acetate exhibits virtually no absorption of UV radiation at 290-300 nm. On the other hand, acetaldehyde has an extinction coefficient of 14 at 290 nm and an extinction coefficient of 15 at 300 nm. Therefore acetaldehyde can act as a photo-sensitizer for the polymerization of vinyl acetate at wavelengths above 299.8 nm [23]. At 366 nm, 2,2 -azo-bisisobutyronitrile has been used as a sensitizer [29,180]. Azobicyclohexane carbonitrile is a UV sensitizer suitable for use with a 124 watt mercury arc at 25°C which does not produce a dark reaction in rotating-sector experiments. Its absorption peak is at 350 mn with an extinction coefficient of 16 [181]. 

Studies [126] of electronic structures in photo-isomerization and photo-dimerization of cinnamic acid showed that phosphorescence of cinnamic groups occurs at about 20,000/cm. Also, it was demonstrated when photo sensitizers are present, the critical distance between donor, sensitizer, and acceptor molecules (cinnamic acid) is about 10 A [126]. Although all the details of incipient photocross-linking of poly(vinyl cinnamate) have to date stUl not been fully worked out, most accept that all three mechanisms take place. These are dimerizations to truxillic and truxinic acid type structures and polymerizations through the double bonds. The excited states of the molecules can be produced by direct irradiation and also through intersystem crossing from an appropriate photosensitizer [126]. 

For the UV hght photo initiated polymerization of aerylonitrile, with 3-amino-9-ethyl-carbazole as a sensitizer, the following kinetie equation for the polymerization was developed... 

Since the discovery of PTFE a considerable research efforts focused on the photo-initiated polymerization of TFE. Polymer has been produced in the mercury-sensitized photolysis of gaseous TFE. However, analysis showed perfluorocyclopropane to be the main product. At pressures less than 8 kPa it is reported to be the only product [695,696]. Photopolymerization of gaseous TFE has also been reported in the presence of mercury bromide, phosgene, and nitrous oxide [697 99]. Atkinson [697] has observed that mercury bromide activated by light of 365 nm initiates the photochemical polymerization of TFE. 

HPDLCs are fabricated by photo-polymerization induced phase separation (PIPS) method by exposing a mixture of LC(s) and photo-sensitive monomer(s) to a laser optical interference field [38 1]. The laser optical field is created by two or multiple coherent laser beams. The periodic structure in HPDLCs is composed of alternating lamellas of polymer-rich layer and phase-separated LC-rich layer, in... 

Schiff-base or imine bonds are also available as pH-sensitive crosslinkers. Because imine bonds are degradable at weakly acidic pH values, endosome-specific dissociation can be achieved by imine-based crosslinking. A simple imine-based crosslinker, glutaraldehyde, has been used to stabilize a DNA delivery system [111]. Photo-induced polymerization [112], epoxide reaction [113], and Michael addition [114] have also been reported as crossUnking methods. However, because... 

Wang X, Guo X, Zhu Y, Li L, Wu S, Zhang R Synthesis of thermo- and pH-sensitive polyelectrolyte brushes by combining thermo-controUed emulsion polymerization and photo-emulsion polymerization. Chin J Polym Sd 29 490—496, 2011. 

A light modulating cell comprises a pair of substrates, alignment layers disposed on at least one of the substrates and a solution of polymerizable prepolymer and low molecular weight organic material disposed between the pair of substrates. The solution is phase separated and forms a layer of polymeric material and a layer of organic material between the two substrates. An external force may then be applied across the substrates to alter the optical appearance of the layer of organic material from one state to another. A photo-sensitive layer may also be provided in the cell. 

Photopolymers for Holography. Smothers, WiUiam K. Monroe, Bruce M. Weher, Andrew M. Keys, Dalen E. (Exp. Stn. Lab., E. I. du Pont de Nemours and Co., Inc., Wilmington, DE 19880-0352, USA). Proc. SPIE—Int. Soc. Opt. Eng. 1990, 1212 (Pract. Hologr. 4), 20-9 (Eng.). Photo-sensitive films composed of dye, initiator, acrylic monomers, and polymeric film-forming binder, and their use in recording vol. phase transmission and reflection holograms are described. Systematic variation of... 

Several carbonyl-containing peroxide additives have been shown to increase the initial rate of the nonoxidative photo-dehydrochlorination of PVC (54). In studies with polymeric ketones unrelated structurally to PVC, the excited singlet and triplet states of the carbonyl groups in these polymers were found to sensitize 0-0 homolysis at rates approaching diffusion control (55). Similar reactions may well occur in oxidized vinyl chloride polymers. 

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