Photochemical studies polymers

The photochemical studies on polysilane high polymers indicate that they constitute a new class of radiation sensitive materials which undergo primarily... 

In our early photochemical studies we have shown that the quantum efficiency for the type I processes in polymers containing ketone groups is highly sensitive to the location of the ketone group with respect to polymer chain, as shown in structures A and B below... 

Quantum Yields of Photolysis. These photochemical studies on high-molecular-weight polysilanes suggest that these polymers constitute a new class of photosensitive materials. The bleaching studies indicate that significant molecular weight reduction occurs upon irradiation in air or in vacuo, which in turn implies that the polymers are predominantly of the scissioning type. 

Preparation. Although acylsilanes (I) and a, P-unsaturated acylsilanes (II) have been the subject of numerous synthetic and photochemical studies 14, 15), to the best of our knowledge, no acylsilane polymers have been characterized or reported prior to our recent work (ii). 

Photochemical studies of azido-3-phenylcoumarins in solution and in polymer layers have been described. A derivative of NAD" and the corresponding ATP analogue have been synthesized in which a spin label is attached to the N-6-position and an azido function to the C-2 atom of the adenine ring. " Both compounds were shown to be active coenzymes or substrates for various enzymes, and could be covalently incorporated into the enzymes upon photolysis. 

Cellulose. Cellulose has been used as a solid powdered substrate for the study of photophysical and photochemical studies of several organic probes, mostly dyes. Some of the properties of this substrate, namely the capacity of adsorbing molecules both by entrapment and on the surface of the natural polymer (forming in many cases hydrogen bonds) and also the absence (or extremely reduced) of diffusion of oxygen, make this substrate a particularly attractive one for room temperature luminescence studies [75-83]. We recently published some fluorescence and phosphorescence studies of rhodamine dyes [15,81,82], auramine O [81b], 2,3-naphthalimides [84], oxazine [85], acridine orange [86], and cyanine dyes [16, 87, 88] adsorbed on cellulose. 

Chen JP, Gao JP, Wang TX. 1997a. Preparation and photochemical study of soluble optically active block copolymethacrylates and azo containing random copolymetha crylates. J Polym Sci, Part A 35(1) 9 16. 

Bengt Rdnby is Professor of Polymer Technology, The Royal Institute of Technology, Stockholm, Sweden which he joined in 1961. He received his doctor s degree in Physical Chemistry in 1952 from the University of Uppsala, Sweden and was in the United States (1956-1961). He has specialized in free radical reactions of polymers studied by ESR and photochemical methods, polymer degradation and oxi-... 

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

Poly(acrylic acid) and Poly(methacrylic acid). Poly(acryHc acid) (8) (PAA) may be prepared by polymerization of the monomer with conventional free-radical initiators using the monomer either undiluted (36) (with cross-linker for superadsorber appHcations) or in aqueous solution. Photochemical polymerization (sensitized by benzoin) of methyl acrylate in ethanol solution at —78° C provides a syndiotactic form (37) that can be hydrolyzed to syndiotactic PAA. From academic studies, alkaline hydrolysis of the methyl ester requires a lower time than acid hydrolysis of the polymeric ester, and can lead to oxidative degradation of the polymer (38). Po1y(meth acrylic acid) (PMAA) (9) is prepared only by the direct polymerization of the acid monomer it is not readily obtained by the hydrolysis of methyl methacrylate. 

Thiophenes continue to play a major role in commercial applications as well as basic research. In addition to its aromatic properties that make it a useful replacement for benzene in small molecule syntheses, thiophene is a key element in superconductors, photochemical switches and polymers. The presence of sulfur-containing components (especially thiophene and benzothiophene) in crude petroleum requires development of new catalysts to promote their removal (hydrodesulfurization, HDS) at refineries. Interspersed with these commercial applications, basic research on thiophene has continued to study its role in electrocyclic reactions, newer routes for its formation and substitution and new derivatives of therapeutic potential. New reports of selenophenes and tellurophenes continue to be modest in number. 

Polyphosphazene films could also be modified very easily by grafting organic polymers onto the surface using chemical, photochemical or y-radiolytic processes. In almost all cases these studies led to the increase in the surface hy-drophilicity and biocompatibility of the phosphazene films without depressing their bulk features. 

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