Picosecond pulse radiolysis and laser flash photolysis studies on polymer degradation of polystyrene and poly-α-methylstyrene

Recently early events in photolysis of polystyrene (PSt) solutions in chloroform and in 1,4-dioxane have been made clear by using a nanosecond laser flash photolysis system (Nd-YAG: 265 nm) at Hahn-Meitner-Institut [1]. Early events in radiolysis of PSt solution have also been studied by using a picosecond pulse radiolysis system at Univ. of Tokyo [2]. In the present paper, the difference and the similarity between photolysis and radiolysis of PSt and poly-α-methylstyrene (P-α-MeSt) are discussed. Important results are as follows; 1. (1) In both cases of radiolysis and photolysis, strong absorptions of intramolecular excimer have been observed for PSt (λmax = 530 nm) and P-α-MeSt (λmax = 520 nm) solutions in dioxane and cyclohexane, in addition to the monomer and excimer fluorescence of these polymers. In these solutions, those polymers are hardly decomposed. 2. (2) In both radiolysis and photolysis, charge-transfer complexes (PSt^+δ, Cl^-δ or P-α-MeSt^+δ, Cl^-δ) have been observed for PSt and P-α-MeSt solutions in chloroform (CHCl₃) and in carbon tetrachloride (CCl₄). In these solutions, polymers are effectively decomposed. The charge-transfer complexes are precursors of macroradicals. 3. (3) The charge-transfer complexes are mainly produced from ion pairs (PST⁺...Cl^- or P-α-MeSt⁺...Cl^-) in the case of radiolysis and from exciplexes of excited polymer molecules with solvent molecules in the case of photolysis. 4. (4) Since the presence of oxygen is prerequisite to main chain cleavage of PSt in CHCl₃ and in CCl₄, it is important to note that oxygen is not involved in initial stages of the main process of macroradical formation.