Cellulose irradiation

A seven-line like signal was detected from carboxymethyl cellulose irradiated with ultraviolet light of 254 nm (Figure 7). When this sample was warmed to ambient temperature for 60 seconds, this multiplet spectrum was transformed rapidly into a prominent doublet signal with a hyperfine splitting constant of 20 gauss. This indicated that the primary free radicals... 

Fig. 12. —Major Volatile Products of Cellulose Irradiated with 4.2 cal. cm. sec. ...

ESR spectra of cellulose irradiated with ultraviolet light have been reported by several authors (126-128). Phillips et al. (127) observed a singlet spectrum with a linewidth of 8-10 gauss after irradiation... 

Arai K, Kawabata Y. 1995. Changes in the sol gel transformation behavior of azobenzene moiety containing methyl cellulose irradiated with UV light. Macromol Rapid Commun 16(12) 875 880. 

The DP of y-irradiated cellulose, as measured by viscometry in cuprammonium solution, has been shown to be lower than that of the untreated cellulose. Irradiation not only induced direct scission of the polysaccharide chains but also the formation of alkali-labile groups, which subsequently underwent scission in the solvent used for viscometry. 

A similar type of condensation between a hydroxyl-containing polymer (such as secondary cellulose acetate) with VO(BrC6H4N=CHO CfiH4)2 CUVOL2CI] produces photoactive polymers [68]. When irradiated with UV light in the presence of styrene or MMA, grafted and crosslinked polymers were obtained ... 

Figure 8 Optical density (280 nm) versus irradiation time (hours) for cellulose triacetate films 0-2,4-DHB D-2H-4BB DHBP-F A-2H-4MB A-HMBP-F and B-HBBP-F.

Photo-induced grafting onto wood cellulose with several vinyl monomers using phenyl acetophenone and benzophenone derivatives as photosensitizers has been reported [72]. A fast increase in grafting was observed for short irradiation times, whereas longer ones resulted in a decreased percent grafting. 

Free radicals can be generated on the cellulose chain by hydrogen abstraction, oxidation, the ceric ion method, diazotization, introduction of unsaturated groups, or by y-irradiation. 

Fig. 6. The CP/MAS spectra of cellulose acetate-butyrate (CAB) and of cellulose acetate (CA, degree of substitution = 1.97), 20. The observation frequency was 50.1 MHz and the irradiation frequency 199.5 MHz. The pulse repetition time was 5 s and the contact time 2 ms. For CAB 400 scans and for CA 60 scans were collected...

Finally, dissolution of non-activated cellulose in LiCl/DMAc, and in ionic liquids has been accelerated by microwave irradiation [72,103,104], although the effect of microwave heating on the DP of the polymer has not been investigated. This last point is relevant in view of the fact that ILs are heated with exceptional efficiency by microwaves [105], so that care must be taken to avoid excessive localized heating that can induce chain degradation of the polymer during its dissolution. 

Bis(tributyltin) oxide is known to break down to inorganic tin under UV irradiation in laboratory conditions (509, 510), and the decomposition may be accelerated by absorbing the organotin compound on a cel-lulosic matrix (511). As bis(tributyltin) oxide is known to react rapidly with carbon dioxide (atmospheric, or trapped in various cellulosic materials, such as cotton or wood) (512), to form bis(tributyltin) carbonate, (BusSnO)2CO, the observed UV degradation pattern may be rationalized in terms of more-ready breakdown of the carbonate than of the oxide, due to the presence of the carbonyl chromophore. The half-life of bis(tributyltin) oxide in pond water has recently been given as 16 days (513). Diorganotin compounds have also been shown to decompose to inorganic tin under UV irradiation (514, 515). 

The compound exists normally as the trans or ( )-isomer 21a. This molecule is essentially planar both in the solid state and in solution, although in the gas phase there is evidence that it deviates from planarity. When irradiated with UY light, the ( )-isomer undergoes conversion substantially into the cis or (Z)-isomer 21b which may be isolated as a pure compound. In darkness, the (Z)-isomer reverts thermally to the (F)-isomer which is thermodynamically more stable because of reduced steric congestion. Some early disperse dyes, which were relatively simple azobenzene derivatives introduced commercially initially for application to cellulose acetate fibres, were found to be prone to photochromism (formerly referred to as phototropy), a reversible light-induced colour change. C. I. Disperse Red 1 (22) is an example of a dye which has been observed, under certain circumstances, to give rise to this phenomenon. 

Thus polyacrylates tend to cross-link, while polymethacrylates tend to degrade, for example. Cellulosics also tend to degrade when irradiated. 

In a recent study, this so-called SPOT synthesis was applied for the preparation of pyrimidines [45]. The group of Blackwell described primarily the appropriate support modification of commercially available cellulose sheets (Scheme 7.28). The initial introduction of the amine spacer was achieved within 15 min utilizing micro-wave irradiation, as compared to 6 h by conventional heating. The acid-cleavable Wang-type linker was attached by classical methods at ambient temperature. 

An 8000-member library of trisamino- and aminooxy-l,3,5-triazines has been prepared by use of highly effective, microwave-assisted nucleophilic substitution of polypropylene (PP) or cellulose membrane-bound monochlorotriazines. The key step relied on the microwave-promoted substitution of the chlorine atom in monochlorotriazines (Scheme 12.7) [35]. Whereas the conventional procedure required relatively harsh conditions such as 80 °C for 5 h or very long reaction times (4 days), all substitution reactions were found to proceed within 6 min, with both amines and solutions of cesium salts of phenols, and use of microwave irradiation in a domestic oven under atmospheric reaction conditions. The reactions were conducted by applying a SPOT-synthesis technique [36] on 18 x 26 cm cellulose membranes leading to a spatially addressed parallel assembly of the desired triazines after cleavage with TFA vapor. This concept was later also extended to other halogenated heterocycles, such as 2,4,6-trichloropyrimidine, 4,6-dichloro-5-nitropyrimidine, and 2,6,8-trichloro-7-methylpurine, and applied to the synthesis of macrocyclic peptidomimetics [37]. 

Ultraviolet irradiation (for cellulose), for covalent ligand immobilization,... 

Two commercial disazo disperse dyes of relatively simple structure were selected for a recent study of photolytic mechanisms [180]. Both dyes were found to undergo photoisomerism in dimethyl phthalate solution and in films cast from a mixture of dye and cellulose acetate. Light-induced isomerisation did not occur in polyester film dyed with the two products, however. The prolonged irradiation of Cl Disperse Yellow 23 (3.161 X = Y = H) either in solution or in the polymer matrix yielded azobenzene and various monosubstituted azobenzenes. Under similar conditions the important derivative Orange 29 (3.161 X = N02, Y = OCH3) was degraded to a mixture of p-nitroaniline and partially reduced disubstituted azobenzenes. 

Considering that severe health hazards and diseases that can be induced by the adhesion and proliferation of bacteria on the surface of numerous materials, bioactive materials incorporated in the surfaces will be required. The cellulose-functionalised with porphyrin 69-71 and 80 were shown to kill gram positive and gram negative bacteria upon irradiation with visible light. Such materials could be used in industrial, household and medical environments, and more generaly in areas that would benefit from permanent and efficient surface disinfection.62 64... 

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