Photosensitive polymers, thermally

When the non-polymerizable acceptor, CH3CN, is used instead of AN, the polymerization of VCZ is again very photosensitive. Although thermal polymerization is too slow to obtain accurate rate measurements, the mechanism is mostly cationic since the yield of polymer is not affected by oxygen and DPPH whereas ammonia and water retard polymerization. The illuminated system seems to be a mixture of cationic and radical polymerization. The effect of ammonia shown in Fig. 3 provides support for a duality of propagation mechanisms. 

Lastly, the polyimide has some inherent photosensitivity. The use of a photosensitive polymer requires fewer processing steps, which also implies an increased yield for the circuit. Ciba-Geigy announced the formulation of inherently photosensitive polyimides in 1985.(5) The use of an inherently photosensitive polyimide is attractive because no sensitizers are added to contaminate the final resin, no functionality is added which degrades the thermal and chemical resistance, and fewer volatiles are present to contaminate the resin or equipment than in some other approaches to photosensitive polyimides. Recent work has shown that these polyimides crosslink on irradiation through hydrogen abstraction by triplet benzophenone and subsequent coupling of the resultant radicals. ... 

Macdonald and C.G. Willson, Poly(N alkysl o nitroamides) A new class of thermally stable photosensitive polymers, in Polymer Materials for Electronic Applications, ACS Symposium Series 184, E.D. Feit and C. Wilkins, Jr., Eds., American Chemical Society, Washington, D.C., pp. 73 82 (1982). A. Reiser, Photoreactive Polymers The Science and Technology of Resists, p. 267, John Wiley Sons, Hoboken, NJ (1989). 

The last examples clearly demonstrate that photosensitive low molecular film-forming ISA complexes are viable alternatives to photosensitive polymers. The ISA complexes have several advantages in comparison to functionalized polymers (i) low production cost due to cheap starting materials (ii) ability to induce higher values of anisotropy (iii) thermal stability of induced anisotropy and (iv) solubility of ISA complexes in environment-friendly solvents such as ethanol. 

Highly aromatic and photosensitive polymers such as polyimides are potential candidates in photonic applications. Wholly aromatic polyimides (XXXV) were observed to be white in color and soluble in polar aprotic solvents such as DMAc, DMF, HMPA, and NMP, whereas the polymers with m-phenylene units in backbone were also soluble in common organic solvents such as acetone, chloroform, and THE All the materials showed excellent thermal stability up to 300° C in air without any weight loss, although initial weight losses of 5 and 10% were observed in the temperature ranges of 362-372° C and 376-384° C, respectively [350]. 

ABSTRACT A new class of photosensitive, thermally stable polymers containing photo-labile aromatic amide linkages has been prepared. These polymers can be used to provide lithographic relief images for printing, etch masks for microcircuit fabrication and as contrast media for optical information storage. 

Polymers with other pendant photosensitive moieties such as 0-furylacrylic ester (2) or / -styrylacrylic ester (5) are highly photosensitive and have even higher photosensitivity after the addition of photosensitizers. However, the thermal stability of these polymers is inferior to that of the polymer with pendant cinnamic esters (4). Polymers with pendant benzalacetophenone (5), styrylpyridinium (6), a-cyanocinnamic ester (7) or a-phenylmaleimide (8) have high photosensitivity but they can not be sensitized. In addition, the photosensitive moieties that are used in the syntheses of these polymers are not commercially available, in contrast to cinnamic acid. 

As already shown, the sensitized spectra follow the dye absorption. Most of the dyes have sufficiently narrow absorption bands. This does not permit us to obtain the panchromatic sensitivity in the sufficiently broad spectral range. It was proposed to use the polymers with conjugated bonds as sensitizers [21]. The broad diffuse absorption spectra are inherent to such compounds. One can expect higher thermal stability from such sensitizers. In addition the application of binder may be omitted from the preparation of the photosensitive layers, for example, in electrophotography. Polymers with triple bonds, polyphenylenes and polyoxiphenylenes were used as sensitizers [10, 14, 278-280]. The typical results are shown in Fig. 47. The main rules for photoconductivity sensitized by polymers were the same as for the dyes. Optimum sensitization was obtained at the concentration of the sensitizer of 10 1-10-2 g/cm3 relative to the polymeric photoconductor weight. 

Polypyrrole polymers have a maximum photosensitivity at 610 and 510 nm which increases to 1400 nm after thermal treatment for 24 h at 300 °C [317]. The established thermal activation energy of the photoconductivity excludes the one-step photogeneration process of the charge carriers. 

Oxadiazole derivatives have been tested in the textile industry as antistatic agents for textile finishes,232,233 thermally stable polymers,82, 234,235 fluorescent whiteners,236 oil and water repellents on cotton and wool,237 and blue dyes for polyesters and polyamides.238 Oxadiazole merocyanine dyes have been patented as photosensitizers for silver halide emulsions.239... 

When 14C-benzoin (19) or its methyl ether (20) is used as photosensitizer for polymerizations, more of the sensitizer is incorporated in polymer than can possibly be accounted for by the initiation process. The reactions have the characteristics of mono-radical polymerizations and separate experiments with thermal initiators have shown that transfer to the carbonyl compound is of little importance. It appears that photo-excited states of these compounds, but not the ground states, can engage... 

Long-lived radicals could also be generated in solid polymers by the thermal decomposition of peroxides and by irradiation in the presence of photosensitizers at room temperature 46). 

Curing by light irradiation can be apphed to a variety of polymers. The acrylic family is a typical example of photosensitive monomers. A well-documented review has recently been dedicated to the curing of composites by ultraviolet radiation [45], Photocuring time is much shorter than for traditional thermal curing (minutes rather than hours), leading to a significant reduction in the cycle time. 

---