Hydroxylated polymers photolysis

Polyolefins.— The mechanism(s) of polyolefin photo-oxidation continue to be shrouded in complexities. Recently Geuskens has attempted to answer questions concerning the sensitized photolysis of hydroperoxides in these polymers in the presence of carbonyl groups. In contrast with the theory proposed above,it is suggested that a complex is formed and photolysed to produce a carboxylic acid and an ether directly (Scheme 19) rather than free hydroxyl radicals. 

As shown in Scheme 1.55, chain branching by thermolysis or photolysis, reaction (4), of polymer hydroperoxides (POOH) results in the formation of very reactive polymer alkoxy radicals (PO-) and hydroxyl radicals ( OH). The highly mobile hydroxyl and polymer alkoxy radical can abstract hydrogen atoms from the same or a nearby polymer chain by reactions (5) and (6), respectively (Zweifel, 1998). These polymer oxy radicals can react further to result in p-scission, by reaction (13), or the formation of in-chain ketones by reaction (14), as shown in Scheme 1.57, or can be involved in termination reactions. 

Figure 11.10 Synthesis of a block copolymer capsule containing FegOs nanoparticies. Photolysis of the cinnamic ester groups of PCEMA to cyclobutanes cross-links the polymer. Hydroxylation of the double bonds of the PI units makes the particles water-soluble. Hydrolysis of the fert-butyl acrylate (PEBA) units gives acrylic acid units which bind Fe(II). Oxidation of Fe(II) in base produces Fe20j. (Reproduced with permission from R. S. Underhill and G. Liu, Chem. Mater. 2000,12, 2082.)...

Photolytic. Photolysis products include carbon monoxide, ethylene, free radicals and a polymer (Calvert and Pitts, 1966). Anticipated products from the reaction of acrylonitrile with ozone or hydroxyl radicals in the atmosphere are glyoxal, formaldehyde, formic acid and carbon dioxide (Cupitt, 1980). The major product reported from the photooxidation of acrolein with nitrogen oxides is formaldehyde with a trace of glyoxal (Altshuller, 1983). Osborne et al. (1962) reported that acrolein was stable at 30°C and UV light (2. = 313 nm) in the presence and absence of oxygen. 

Polyethylene segments can form a cage, which allows for fast reaction between a polymer alkoxy (PO ) radical and a hydroxyl (HO ) radical (formed during the photolysis of the POOH group), resulting in the formation of a carbonyl group and water [383] ... 

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