Hydrogen abstraction poly

Similarly, energy-transfer processes, together with electron transfer and hydrogen abstraction reactions could be induced in poly(organophosphazenes) in an intramolecular way by preparing POPs geminally substituted at the same phosphorus with two different substituent groups. 

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. 

Figure 6. Relationship between yields of low molar mass nitrogen-containing products resulting from elimination of a section of the main chain and hydrogen abstraction radical from the irradiation of poly(amino acid)s at 25° C. (A) tyr, (A) phe, ( ) gly, (O) ala, ) val.

Wu JC, Kozarich JW, Stubbe J (1985a) Mechanism of bleomycin evidence for a rate-determining 4 -hydrogen abstraction from poly(dA-dU) association with the formation of both free base and base propenal. Biochemistry 24 7562-7568... 

Decomposition of the Pd M P species via /1-hydrogen elimination is unfavourable, since both /1-hydrogen atoms, H3 and Hi, are not easily accessible for a Pd-H bond forming process. The suppression of /1-hydrogen abstraction is a prerequisite for the monomer undergoing m-insertion polymerisation, leading, in this case, to poly(2,3-bicyclo[2.2.1]hept-2-ene) [10]. 

Such a structure of poly(carbonmonoxide-a/r-norbornene) is due to the lack of /i-hydrogen abstraction from the norbornene monomeric unit bound to palladium. 

Analogous considerations have been invoked [23] in order to explain the shorter lifetime of the triplet state in poly(VBP) against free benzophenone in the presence of THF and the higher efficiency of the polymeric system in the photoinduced hydrogen abstraction from the above solvent (Table 3) as well as in... 

Table 3. Triplet state lifetime (r) of poly(VBP) and benzophenone (BP) in benzene as a function of tetrahydro ran concentration [THF] and rate constants (ka) of hydrogen abstraction from THF at room temperature in the same solvent [23]...

Finally, as the above experiments have been performed in benzene, a very weak hydrogen donor, they clearly indicate that in poly(ABP) the hydrogen abstraction occurs through an intramolecular mechanism. 

The decrease in solubility upon exposure in this type of resist was first ascribed to the formation of a secondary amine generated from nitrene insertion into C-H bonds of the polymer (see Scheme 3.6) (88). However, gel permeation chromatographic analyses revealed that the molecular weight of poly(p-vinylphenol) increased upon irradiation in the presence of the azide. Hydrogen abstraction from the polymer by nitrene and subsequent polymer... 

Hydrogen Abstraction of Benzophenone Triplet in Poly(vinyl alcohol)... 

In order to know the net quantum yield for the benzophenone disappearance, 4i(-BP), by hydrogen abstraction in poly(vinyl alcohol), the change in UV spectra of benzophenone at 256 nm in the poly(vinyl alcohol) film was followed during continuous Irradiation of 365 nm UV light. The (-BP) given in Table III is very small for T < T, suggesting the predominant occurrence of backward reaction (k , ) of benzophenone ketyl radical in the... 

The evidence for this mechanism is two-fold the presence of aromatic moiety in the resulting poly-glycol and the quantitative analysis of the solution left after precipitation of the polymer, demonstrating only one-half of the utilized naphthalenide being converted into naphthalene. (it has been claimed that at very low concentrations of the naphthalenide, polymers with only one growing group were formed ( 0), Hydrogen abstraction from solvent was proposed as an explanation. 

Solid state irradiation of -aminobenzoylazide in the absence of a binder leads to formation of the polyurea. Attempted formation of such a polymer within a matrix of a soluble polymeric binder such as poly-(vinylbutal) led to insolubilization in the exposed areas. Hydrogen abstraction can simultaneously produce crosslinking of the binder. 

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