Photo-oxidative degradation of polystyrene

Photo-oxidative degradation of polystyrene occurs in a very broad spectral range (254nm-400nm). 

These results show that photo-oxidation (A 300 nm in O2), as indicated by random chain scission, occurs in two distinct stages  

The pure photoprocess, which is independent of O2, is largely complete before the onset of appreciable oxidation, as reflected by the progressively increasing extent of chain scission. 

Photolysis of oxidative products (hydroperoxide groups, chain peroxides and ketonic groups) formed during the preparation of polystyrene. If hydroperoxides are present (Fig. 3.51) the oxidation rates are increased, and degradation can also be induced in the anionic polystyrene. 

Absorption of oxygen initially results in the formation of hydroperoxides easily detected in the IR spectrum in the region 3200-3400/cm (Fig. 3.52). Their concentration increases linearly with time whereas in the auto-oxidation of polymers it usually passes through a maximum corresponding to the beginning of the autocatalytic stage of the oxidation process. 

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The mechanism of photo-oxidative degradation of polystyrene was also investigated using low molecular compounds such as benzene 3-phenyl-pentane [1356] 2-phenylbutane [1360, 1361] 1,3-diphenylpropane-l-one [719, 725] 1,3-diphenylpropane 1,3-diphenylbutane 2,4-diphenylpentane [1293] cumene cumene hydroperoxide [759] acetophenone hexanoic acid 3-heptanone y-valerolactone 2-phenyl-2-propanol [1250, 1397] benzal-dehyde benzoic acid l-3-diphenyl-propanone-3 l,3-diphenyl-buten-2,3-on-l (dypnone) l,3-diphenylpropen-2,3-on-l (chalcone) l-phenyl-butanedion-2,3 l-diphenylpropanedion-1,2 l-phenyl-butanedion-1,3 phenylacetic aldehyde l,5-diphenyl-pentanone-3 4-phenyl-butanone-2 [1250]. 

The rate of the photo-oxidative degradation of polystyrene in halomethanes increases in the order methylene chloride < chloroform < carbon tetrachloride, i.e. it increases with increasing electron affinity of the solvent [279]. Photodegradation of poly(a-methylstyrene) in carbon tetrachloride by... 

In conclusion, singlet oxygen plays a role in the photo-oxidative degradation of polymers containing olefinic unsaturations. Polymers that do not contain these groups, e.g. poly(vinyl chloride), poly(methyl methacrylate), polystyrene, etc., are unreactive [24]. 

A review of the photo-degradation of polystyrene includes a mechanism proposed to explain the breakdown of that polymer. A novel technique for following the extent of photo-oxidation of bulk polymer has been developed by Weir who measured the dielectric loss of films during irradiation in vacuum and in oxygen. Under these conditions the increases in dielectric constant were attributed to products of degradation, and measurement of the loss-peak due to carbonyl compounds provided a sensitive indicator of extent of reaction. - A study of the role of stabilizers showed that for specific types the stabilization mechanism involved the screening effect as well as the ability to quench excited states of the polymer. A study of photo-oxidation (A>300nm) of films of styrene-type copolymers produced a mechanism in which it was proposed that initiation of the... 

Traces of copper or iron scarcely influence the photo-oxidative stability of PPE. However, if PPE containing copper or iron compounds is mixed with impact modified polystyrene (SB), the result is a significant reduction in photo-oxidative stability. Iron(III)chloride causes strong degradation, followed by copper(II)chloride and acetate the least damaging is iron(III)acetate [86]. 

Polystyrene can form a charge-transfer (CT) complex with molecular oxygen [36, 1386, 1610, 1611, 1781, 1793, 1794, 2301]. The absorption band of the CT complex extends from 350 nm toward longer wavelengths [1610]. High oxygen pressure promotes the formation of the CT complex [1794] and the rate of photo-oxidation, but does not influence the mechanism of photo-oxidative degradation [1610, 1793]. The concentration of the CT complex depends on two factors ... 

Initiation of the photo-oxidative degradation is due to the presence of internal chromophoric impurities, which can absorb UV radiation (section 3.11.1.2). The nature of these chromoirfiores has been the subject of several investigations and considerable controversy. Figure 3.50 shows the effect of UV irradiation in oxygen (1 atm) on the various polystyrenes. 

Rabek [498, 505] examined the rapid degradation of cis-1,4-polyisoprene on exposure to light in the presence of p-quinones p-quinone, chloranil, 1,4-naphthoquinone, anthraquinone, phenanthrene-quinone and 1,2-benzanthraquinone (Fig. 20). Later, Rabek [504] also found that p-quinone sensitizes the photo-oxidation of polystyrene in benzene in the presence of UV radiation. 

Rabek [504] found that anthracene sensitizes the degradation and photo-oxidation of polystyrene in solution. It also sensitizes the degradation of cis-polybutadiene in benzene solution. 

Wojtczak have found that the photosensitized degradation of polyethylene glycols decreases in the order triethylene glycol > polyethylene glycol 400 mol. wt. > polyethylene glycol 4000 mol. wt. Sastre and Gonzalez have shown that bromoalkanes are powerful sensitizers for the photo-oxidation of polystyrene, and Rabek and Ranby have found that polynuclear aromatics are photosensitizers for polybutadiene. Aromatic carbonyls have been shown to induce free-radical formation in cellulosic materials. 

The photo- and thermooxidative degradation of different grades of high-impact polystyrene containing various amounts of polybutadiene were studied using FTIR spectroscopy. All samples gave similar oxidation products, but in varying quantities. The results are discussed. 17 refs. 

F. A. Bottino, G. Di Pasquale, E. Fabbri, A. Orestano, and A. Pollicino, Influence of montmorillonite nano-dispersion on polystyrene photo-oxidation. Polymer Degradation and Stability, 94 (2009), 369-74. 

Polystyrenes are one of the most extensively investigated polymers with respect to photo-degradation and photo-oxidation. A considerable body of literature (cf. Table 3.17) has been published over the years but a consistent theory has failed to emerge and, in some cases, contradictory hypotheses have been presented, indicating the complexity of the mechanism involved. 

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