Polyisoprene singlet oxygen

Hexahydropyrene sensitized chain scission of polypropylene and polyisobutylene during light irradiation Q20).Polycyclio hydrocarbons have a important role in sensitized photooxidation of polyisoprene (122).polys tyrene (123) poly(methyl methacrylate) (123-126). It is quite probable that these reactions can also occur with participation of singlet oxygen. 

Rabek (66) has assumed that in the case of singlet oxygen reaction with polyisoprene,double-bond shift cccurst... 

This reaction was reported for the benzophenone photosensitized degradation of polypropylene (92),polystyrene (95), poly(vinyl alcohol) (94),polyisoprene (95,96),polyurethane (97) and polyadenylic acid (98) In solid state benzophenone also produce an extensive crosslinking of polyethylene (99-105) It has also been found that benzophenone and its derivatives caused an initial rapid oxidation,increasing with ketone concentration (70) Currently the relative importance of singlet oxygen formation in energy transfer reaction between excited benzophenone and molecular oxygen is discussed (92,104) ... 

This prompted us to review the work on the decomposition of hydroperoxides and in particular to determine what portion of the hydroperoxides that decomposes leads ultimately to bond scission. It is important to point out in this context that it is possible in principle for a polymer to oxidize extensively without losing its physical properties. The most important process in the breakdown of physical properties is bond scission in the backbone of the polymer chain. This can be best determined by measurements of the molecular weight of a photooxidizing or photodegrading polymer. In our laboratories we have studied this process by automatic viscometry which permits a very precise measurement of bond scission in polymers the apparatus has been described previously (12). For these studies we prepared a singlet-oxygen adduct of cis-polyisoprene by the following scheme ... 

Following Ashby s first observation (7) of chemiluminescence from the oxidative degradation of polymers, a number of papers have appeared dealing with oxidative chemiluminescence from a variety of polymers (8-16). In this chapter we continue the 1,4-polyisoprene work with a study of the low-temperature chemiluminescence emitted in the autoxidation of three additional elastomers, cis-1,4-polybutadiene, amorphous 1,2-polybutadiene, and fmns-polypentenamer. We also report the chemiluminescence obtained from singlet-oxygenated samples of cis-1,4-polybutadiene and trans-polypentenamer, as well as rate data for singlet oxygen reactions with the 1,4-polyisoprene, 1,4-polybutadiene, and model compounds in solution. 

Except for the autoxidized 1,2-polybutadiene values, all of the Ea values in Table I were equal to or less than those found earlier for autoxidized or singlet-oxygenated cis-1,4-polyisoprene (I). 

Values for Polymer and Model Compounds. 1,4-Polyisoprene and 1,4-polybutadiene are so sufficiently reactive toward singlet oxygen that we can conveniently obtain / -values by three methods (a) from oxygen-uptake rates by photosensitized oxidation at different polymer concentrations (b) by the initial disappearance rate of rubrene on photooxygenation of solutions with and without polymer (or model olefin) and (c) for 1,4-polyisoprene, by the amount of rubrene consumed upon addition of aliquots of triphenyl phosphite ozonide in the presence and absence of olefin or polymer. The treatment of data from methods (b) and (c) was modified to give /3-values directly from the following equations ... 

Photo-oxidation of cis-polybutadiene was also shown to involve singlet oxygen [570]. Attacks by singlet oxygen on double bonds with formation of allylic hydroperoxides and shifts of these double bonds according to the ene reaction were confirmed by several other studies [571]. On the other hand, a study of model compounds for photo-oxidation of polyisoprene failed to show formation of endo peroxides by 1,4-cycloaddition [572]. 

Polyisoprene.—Several papers have been published on the kinetics and mechanism of the photo-oxidation of polyisoprene induced by singlet oxygen/ " The trans >C=C< groups were found to be more reactive than the cis groups/ ... 

Polydienes (polybutadiene, polyisoprene and their copolymers and analogues) react very effectively with singlet oxygen CO2) generated in the gaseous phase by microwave discharge or in photosensitized (dye) reactions. Reaction of 02 with polyisoprene leads to the formation of three polymeric hydroperoxides [800, 1569, 1571, 1572, 1787, 2095, 2096] ... 

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