Photosensitized oxidation of unsaturated polymers

Abstract

-The photosensitized oxidation or singlet oxygenation of unsaturated hydrocarbon polymers and of their model compounds is reviewed. Emphasis is on work in this laboratory on cis and trans forms of 1,4-polyisoprene, l,4-polybutadiene and l,2-pcly(l,4-hexadiene), and on l,4-poly(2,3-dimethyl-1,3-butadiene) (cis/trans ratio 44:3). The microstructural changes which occur in these polymers on reaction with 102 in solution were-investigated by infrared, 1H and 13C NMR spectroscopy. The polymers were shown to yield allylic hydroperoxides with shifted double bonds according to the "ene" mechanism established for simple olefins. A convenient infrared measure of polymer hydroperoxidation was afforded by the absorbance ratio, A29/A69A' .Smooth correlations of A' with oxygen uptake were obtained with chlorophyll or methylene blue as photosensitizer, but Rose Bengal gave erratic A'-O2 uptake data indicative of autoxidation accompanying the hydroperoxidation. The photosensitized oxidation of the above unsaturated polymers exhibited zero-order kinetics, the relative rates paralleling the reactivities of the corresponding simple olefins towards 102. Two other polymers, 1,2-polybutadiene and 1 ,2-poly(trans-l,3-pentadiene), showed negligible reaction with 102, reflecting the extremely low reactivities of their simple olefin analogs. This work demonstrated that singlet oxygenation of unsaturated polymers does not differ fundamentally from that of their low molecular weight analogs; such differences as do arise are due to secondary processes affecting the 102-reacted polymers. The occurrence of degradation in singlet oxygenation of unsaturated polymers is discussed.

“Inside” vs “Outside” Photooxygenation Reactions: Singlet-Oxygen-Mediated Surface Passivation of Polymer Films

“…6 However, we note that epoxide groups (ring vibration) would also absorb at ∼905 cm -1 . 6 The apparent shift in the peak maximum of the band at ∼905 cm -1 upon prolonged irradiation may reflect, among other things, a change in the relative amounts of these functional groups over time.…”

“…This reaction to produce the dCH 2 group is also consistent with the appearance of the characteristic band at 905 cm -1 (Figure 2d). 6 However, the associated appearance of the band at 850 cm -1 suggests that the initial reaction is not 100% selective and that other kinds of double bonds are also formed during the reaction of poly(AN-co-DMB) with singlet oxygen. One option is the result of the ene reaction to form the more highly substituted double bond in the macromolecular backbone (Scheme 4).…”

“…3 In contrast, the photosensitized production of singlet oxygen inside bulk polymer samples, and in samples of dissolved polymers, clearly results in polymer oxygenation. 6,20,23,24 singlet-oxygen-mediated oxygenation products spawn subsequent reactions that ultimately lead to macromolecular chain scission. 24 At present, one can only speculate about the possible origins for these differences in "inside" vs "outside" photooxygenation reactions.…”

Impact of photo-induced species in O 2 -containing gases on lithographic patterning at 193-nm wavelength

“…56,[73][74][75][76][77][78][79][80][81][82][83][84] Depending on the availability of an allylic hydrogen, substituent polymers react with it to produce either dioxetanes or hydroperoxides, whereas polydienes yield endo-peroxides. [85][86][87][88][89][90] In polymers, light absorbing impurities (external and/or internal structure irregularities) have been reported to act as potential photosensitizers for generation of singlet oxygen.…”

Photodegradation of some poly(vinyl chloride) (PVC) blends: PVC/ethylene‐vinyl acetate (EVA) copolymers and PVC/butadiene‐acrylonitrile (NBR) copolymers

“…Singlet oxygen ( ' 0 2 ) can also be formed by energy transfer from electronically excited chromophores (including photoexcited carbonyl groups) to molecular oxygen. If it occurs, the singlet oxygen may react with unsaturated bonds in PB (20,(32)(33)(34) and in particularly dehydrochlorinated PVC (polyene bonds) ( 3 5 ) , by an "ene-type" mechanism (36). As a result hydroperoxy (OOH) groups are formed.…”