TWO CLASSES OF PROTECTIVE AGENTS IN 



THE OXIDATIVE DEGRADATION BY GAMMA 



RAYS OF POLYSTYRENE IN CHLOROFORM 



M. Fox 



Laboratoire de Chimie Physique de la Faculte des Sciences de Paris* 



A NUMBER of compounds have been examined as possible protective agents 

 against degradation of polystyrene dissolved in chloroform in the presence 

 of air by gamma rays from a ^"Co source at an intensity of 23 r/min. The de- 

 gradation was measured by the change in viscosity of the solution. Table I 

 shows the results obtained for compounds which have been found effective 

 in a similar investigation using an aqueous polymer system.^ Degradation 

 is reduced by amines, hydroxy compounds and mercaptans (7), and by com- 



pounds having the structure — S— C or — S=C as in thiourea, mercapto- 



benzothiazole and dithiocarbamate derivatives [2) ; aromatic compounds are 

 generally more effective than the aliphatic homologues. In the case of 

 protective agents which are chelating agents, such as 8-hydroxyquinoline 

 and dithiocarbamate, chelation does not suppress the protective action 

 although the complex is less active. 



The viscosity of the polystyrene solution continues to drop for a con- 

 siderable time after irradiation has ceased {see Table If). The effect of 

 Co2+ ions is consistent with the view that the degradation is due to decom- 

 position of a polymer peroxide resulting from electron transfer ^ : 



ROOH + Co2+ = RO* + OH- + Co3+ 



decomposes. 



The post effect is not found when the irradiation is carried out in the 

 presence of protective agents of the thiourea type but occurs in other cases 

 as shown in Table I. Moreover the former type of compoimd when added 

 after irradiation reduces the post-effect, other protective agents act in the 

 opposite sense, accelerating the degradation as shown in Table I (cf. the 

 action of phenols on hydroperoxides^). It seems therefore that the two 

 classes of protective agents react in a different manner. The kinetics of the 

 reaction of ^-naphthol as a function of the degradation have been investigated 

 in some detail*. The results show that the degradation which is initially 

 inhibited resumes its normal course, at a dose which is proportional to the 

 concentration of [i-naphthol. Assuming reaction of (i-naphthol with primary 

 solvent radicals it is found that the protective agent reacts with only a small 



* British Council and Medical Research Council Exchange Fellow ; Present address : 

 Chester Beatty Research Institute, Royal Cancer Hospital, London, S.W. 3. 



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