Poly , photolysis

Pyridinium ylide is considered to be the adduct car-bene to the lone pair of nitrogen in pyridine. The validity of this assumption was confirmed by Tozume et al. [12J. They obtained pyridinium bis-(methoxycarbonyl) meth-ylide by the photolysis of dimethyl diazomalonate in pyridine. Matsuyama et al. [13] reported that the pyridinium ylide was produced quantitatively by the transylidalion of sulfonium ylide with pyridine in the presence of some sulfides. However, in their method it was not easy to separate the end products. Kondo and his coworkers [14] noticed that this disadvantage was overcome by the use of carbon disulfide as a catalyst. Therefore, they used this reaction to prepare poly[4-vinylpyridinium bis-(methoxycarbonyl) methylide (Scheme 12) by stirring a solution of poly(4-vinylpyridine), methylphenylsulfo-nium bis-(methoxycarbonyl)methylide, and carbon disulfide in chloroform for 2 days at room temperature. 

It is possible that such an effect may be masked by the decrease in contact angle upon the photolysis of poly(2-vinylnaphthalene) films as s lown in Figure 5. 

Spatial electrochromism has been demonstrated in metallopolymeric films.28 Photolysis of poly-[Run(L10)2(py)2]Cl2 thin films on ITO glass in the presence of chloride ions leads to photochemical loss of the photolabile pyridine ligands, and sequential formation of po/y-[RuII(Llt))2(py)Cl]Cl and po/y-[Run(L10)2Cl2] (Scheme 1). 

During photolysis, the double bond content of the polysilane(P-l)(15mol% in this experiment) decreased to 10mol%, as measured by 1H-NMR spectroscopy. However, the ratio, quantum yield of scission(Q(S))/quantum yield of crosslinking(Q(X)), was not affected by the reaction of the double bond. West and his coworkers have reported that poly((2-(3-cyclohexenyl)-ethyl)methylsilane-co-methylphenylsilane) crosslinked upon irradiation(55). The difference between our results and West s may lie in the amount of the double bond and inhibitation of the radical closslinking by the phenol moiety. Polysilane with a halogen moiety, P-8, photodecomposed rapidly, compared with P-1 or P-3. The introduction of a chloride moiety was effective for the sensitization of the photodegradation. Similar results has already been reported(55). 

It should additionally be noted that a number of the paths of the schemes above have received some confirmation in a number of literature reports dealing with the photolysis and photo-oxidation of other polyesters [32-35], Because these reports investigated poly(butylene terephthalate) (PBT), poly(ethylene naphthalate) and poly(butylene naphthalate), however, they may not have direct application to understanding of the processes involved in PET and PECT and so have not been discussed in this present chapter. All do contain support for the formation of radicals leading to CO and C02 evolution, as well as the hydrogen abstraction at glycolic carbons to form hydroperoxides which then decompose to form alkoxy radicals and the hydroxyl radical. These species then were postulated to undergo further reaction consistent with what we have proposed above. 

Photolysis of the unsubstituted poly(ethylene sebacamide) (A), methylated poly(l,2-propylene sebacamide) (B), and poly(l,l-dimethylethylene sebacamide) (C) resulted in mostly chain fragmentation as indicated by the decreases in intrinsic viscosities of the polymer samples, Table 1. The same decrease in intrinsic viscosity was also observed for polyurea D. Polymer A and D remained bio-inert under the testing condition whereas the abilities for polymers B and C to support the growth of Apergillus niger were improved by photolysis. 

Photolysis of hydiroxylated polymers E, F, G, benzylated polymers H and I, and poly(piperazinyl sebacamide) J all resulted in crosslinking as the polymer samples became insoluble after photolysis. Interestingly enough, however, with the exception of polymer H, all polymer samples were found to be better carbon nutrients for the fungus Aspergillus niger after photolysis. 

Photolysis of Transition-Metal Poly hydride Complexes 363... 

Surface Water In an estuary, the half-life of chlorpyrifos was 24 d (Schimmel et al., 1983). Photolytic. 3,5,6-Trichloro-2-pyridinol formed by the photolysis of chlorpyrifos in water. Continued photolysis yielded chloride ions, carbon dioxide, ammonia, and possibly poly-hydroxychloropyridines. The following photolytic half-lives in water at north 40° latitude were reported 31 d during midsummer at a depth of 10 cm 345 d during midwinter at a depth of 10 ... 

Laser flash photolysis experiments showed that the Ceo triplet state ( C q), obtained by 532 nm excitation, reacts with poly(methylphenylsilane) by an... 

The cross sections for formation of the two dimers are similar, but not identical, with those for the formation of two of the dimers from UpU, and the wavelength dependencies are similar. Hydrate formation occurs more rapidly in d-UpU than in UpU. The marked quantitative and qualitative differences in the photochemistry of these two closely similar dinucleotides, along with the additional difference in results observed with poly U, to be discussed below, make it clear that the factors influencing the course of the photolysis of polynucleotides are not well known. It must be pointed out that the structures of the various... 

Multiple products, as observed in the photolysis of TpT, seem likely to be formed in the photolysis of poly T but will only be discovered by a detailed product analysis. 

The quantum yield for loss of absorbance in the photolysis of poly C (corrected approximately for change in hypochromoaticity) is about 7.5 x 10"3, and the thermal reversibility is about 85T,.7 The hypochromoaticity of poly C is high (about 40%). The thermal reversal rate as a function of temperature has been reported by Ono, Wilson, and Grossman82 1 (Fig. 34). 

Setlow et al.83 have studied the photolysis of poly dl poly dC (polydeoxyinosinic acid polydeoxycytidylic acid, see Glossary) and poly dA dT. The photochemical changes were estimated by following absorbance changes, by chromatographic separation of acid hydrolysates, and by chromatographic separation of products from enzymatic hydrolysates. 

The existence of photoreversible, but not of heat-reversible, absorbance change in irradiated poly dI dC was taken to prove that the photoproducts are entirely dimers (in contrast to those in poly C irradiations where the product is almost entirely the hydrate82a). It was possible to detect dimers of uracil as well as those of cytosine, by means of the much slower photoreversal of uracil dimers. In the acid hydrolysates of irradiated dl-dC, both uracil dimers and uracil could be identified. Enzymatic hydrolysis (snake venom phosphodiesterase) does not split pyrimidine dimers, and the products of such hydrolysis of irradiated tritium-labeled poly dl dC contained trinucleotides shown by radioactivity to contain cytosine dimers. Thymine dimers were formed in the photolysis of the poly dA dT, and were detected and assayed by the same methods. The yield of thymine dimers in irradiated poly... 

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