Photolysis polystyrene

Polystyrene Solution in CHClj and CCl. In the laser photolysis and pulse radiolysis of polystyrene solution in CHC13 one observes an absorption spectra with maxima at 320 nm and around 500 nm (2,4,17). as shown in Figure 12. 

Examples of radical-mediated C-alkylations are listed in Table 5.4. In these examples, radicals are formed by halogen abstraction with tin radicals (Entries 1 and 2), by photolysis of Barton esters (Entry 3), and by the reduction of organomercury compounds (Entry 4). Carbohydrate-derived, polystyrene-bound a-haloesters undergo radical allylation with allyltributyltin with high diastereoselectivity (97% de [41]). Cleavage from supports by homolytic bond fission with simultaneous formation of C-H or C-C bonds is considered in Section 3.16. 

The incorporation of diethyldithiocarbamate groups (Et)2N-C-S-R in a polymer produces active sites which on photolysis can be used for graft or block copolymerization depending on the location of the groups (185). By heating polystyrene with tetraethyl thiuram disulfide, Para substitution occurs... 

The photolysis of labile atoms or groups has also been described. The photobromination of polystyrene occurs essentially in a-position... 

This value agrees with the lifetime of the excimer of polystyrene. The intensity of the excimer fluorescence decreased with increasing chloromethylation ratio. Electrons produced in cyclohexane, one of the precursors of the excimer, were scavenged by chloromethylated part of polystyrene. Absorption spectra of the excited states and the polymer radicals were measured by laser photolysis of the cyclohexane solutions. The results are summarized in Fig. 10 [67]. 

Polystyrene, its copolymers, and its alloys are used in a wide variety of applications where stability to both direct sunlight and filtered or artificial lighting is important. At wavelengths below 300 nm photolysis [12] of polystyrene can result in unacceptable color development (yellowing) along with reduction of physical prop-... 

The main reactions taking place when chloromethylated polystyrene (CMS) and chloromethylated poly(diphenylsiloxane) (SNR) are irradiated with high energy electrons or deep UV (KrF excimer laser, 248 nm) radiation have been studied. The results are discussed in terms of short-lived reactive species generated using pulse radiolysis and laser (248 nm) photolysis techniques. 

Details of the laser photolysis system have been reported elsewhere (19). Polystyrene or CMS in cyclohexane solution in a 1x1x2 cm quartz cell was excited by a 248-nm pulse from a KrF excimer laser (lambda Physik EGM 500). The width of the pulse was 15 ns (full width at half-maximum (FWHM)). Transient spectra were monitored point by point by using a conventional nanosecond laser photolysis method. 

Deep UV Resist Reactions of CMS. The laser photolysis studies on CMS and polystyrene solutions in cyclohexane were carried out at 248 nm using a KrF excimer laser. The intensity of monomer and excimer fluorescence of CMS becomes weaker with increasing chloromethylation ratio, but the lifetime of the excimer is essentially independent of the chloromethylation ratio being almost the same as the excimer lifetime of polystyrene (20 ns). The lifetime of the monomer fluorescence has not been investigated by nanosecond laser photolysis because of the short lifetime (about 1 ns) (20,21) of the singlet. 

Fig. 1 shows the transient absorption spectra observed during photolysis of cyclohexane solutions of CMS. The absorption spectrum with the peak at 520 nm (spectrum a) is identical to that of the excimer of polystyrene (spectrum C) (22) and has a similar lifetime of 20 ns. The quenching rate of the absorption at 520 nm by O2 is comparable to what one would expect for the CMS excimer. 

We have recently been concerned about how a polymer environment might affect these two processes. The first question is whether the environment of a solid polymer will increase the amount of primary cage recombination of a dissociating radical pair. Studies were made [21] of the quantum yield for photolysis of benzoyl peroxide in two solvents, benzene and toluene, and in solid polyethylene and polystyrene films ... 

Poly(styrene)s containing acylperoxide groups are thus obtained by selective photolysis of the azo moieties at 350 or 371 nm. These prepolymers are successively used as macronitiators for the free radical polymerization of vinyl chloride at 70 °C. Styrene/vinyl chloride block copolymers are thus produced [55] by the above two-step route, although relevant amounts (50-60%) of poly(styrene) and poly(vinyl chloride), due to both low peroxide content ( 0.6 groups per macromolecule of polystyrene) and chain transfer with solvent and monomer, are also pre t. 

Polystyrene alone or with photosensitizer was unaffected under photolysis conditions, apart from some yellowing, and polystyrene-blsmaleimlde solutions appear to be stable Indefinitely in the dark. Blsmalelmldes have beat used previously in peroxide-Induced crosslinking of polymers l however, polystyrene was reported to be unreactlve under these conditions. Thus, the crosslinking reactions described here are not free radical in nature and are best formulated according to Reaction 3. Blsmalelmldes have also been reported to accelerate the radlolysls-induced crosslinking of elastomers.—... 

In this report we examine the effects of several vinyl ketone monomers on the photodegradation of polystyrene in the solid phase. Previous work Sj has indicated that copolymers containing vinyl ketones undergo photolysis by the Norrish type I and type n primary reactions. Studies by Golemba and Gulllet and by Kato and Yone-shiga 0 have shown that these processes also occur in copolymers of styrene with meUiyl vinyl ketone and widi phenyl vinyl ketone. 

Figure 6. Photolysis of 4 1 blends of polystyrene with polystyrene 5% vinyl ketone copolymers...

The results of early flash studies were irreproducible and led to various conclusions concerning the nature of the primary photoproduct. For example, flash photolysis of Cr(CO)g in room temperature degassed cyclohexane solutions and in polystyrene film was reported to produce a transient having a maximum absorbance in the visible at 450 nm and which decayed with second-order (equal concentration) kinetics (83). The following scheme was proposed for the overall mechanism ... 

Amao, Y., Asai, K., and Okura, I. (2000). A novel optical oxygen sensing system based on triplet-triplet reflectance of fullerene Cgg-polystyrene film by time-resolved spectroscopy using diffuse reflectance laser flash photolysis. Analyst, 125, 523-fi. 

---