Chlorinated poly irradiation

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometaUic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinyhdene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. Without the use of heat stabilizers, PVC could not be the widely used polymer that it is, with worldwide production of nearly 16 million metric tons in 1991 alone (see Vinyl polymers). 

When a neat chlorinated poly(methylstyrene) film is irradiated by 308 nm pulses at low fiuences (e.g., F = 0.23 J/cm, surface roughening due to melting is clearly evident (Fig. 5a). In the intermediate fiuence (/.c., 0.8 J/cm F 0.4 J/cm, the etched surface is quite smooth (Fig. 5b). The topographical features associated with thermal melting, material flow and resolidification are not so evident from the SEM photos (Fig. 5a) as in the low fiuence region (Fig. 5b). There are formations of bubbles and holes in... 

Polyimides, chlorinated poly(methylstyrene) and novolac resins are all crosslinking polymers under ordinary UV light irradiation, whereas PMMA and PMGI are main-chain scission-type polymers under deep UV irradiation (23). Even for such scission-type polymers, photo-thermal effects cannot be neglected. For crosslinking-type polymers, photo-thermal effects become more important and are the predominant mechanism for photo-ablation. 

Fig. 3.43. Absorption spectra of photodehydrochlorinated chlorinated poly(vinyl chloride) (C-PVC) and after UV irradiation (15 min) and after laser irradiation (488 nm) in air for 0.1 s [554]. (Reproduced with permission from [554] published by John Wiley Sons, 1971.)...

The most innovative photohalogenation technology developed in the latter twentieth century is that for purposes of photochlorination of poly(vinyl chloride) (PVC). More highly chlorinated products of improved thermal stabiUty, fire resistance, and rigidity are obtained. In production, the stepwise chlorination may be effected in Hquid chlorine which serves both as solvent for the polymer and reagent (46). A soHd-state process has also been devised in which a bed of microparticulate PVC is fluidized with CI2 gas and simultaneously irradiated (47). In both cases the reaction proceeds, counterintuitively, to introduce Cl exclusively at unchlorinated carbon atoms on the polymer backbone. 

The flue gas from municipal waste incinerator boilers contains SO2, and HCl. To remove these harmful components simultaneously by dry process, electron beam treatment method was investigated. The pilot-scale test was conducted in Matsudo, Japan, in 1992 with a flue gas of 1000 m /hr [34]. Recently, dioxins, namely, poly-chlorinated-di-benzo-paradioxins (PCDDs) and poly-chrorinated-di-benzo-furan (PCDFs), from incinerators have become a very serious problem because of their high toxicity. Pilot-scale tests to decompose dioxins by electron beam irradiation were conducted in Karlsruhe, Germany [35], and in Takahama, Japan [36], using almost the same capacity of flue gas, 1000 m /hr. Very promising results were obtained with decomposing more than 90% of dioxins. 

In carbon tetrachloride poly(a-methylstyrene) were degraded, even without oxygen, by the irradiation of ionizing radiation [58], The decay of the charge transfer radical complex, observed in this solvent, may be due to the reaction of a chlorine atom with p-site H of poly(a-methylstyrene) the reaction leads to the formation of P-position radicals of poly(a-methylstyrene). The produced polymer radicals were unstable and dissociated into neutral and radical species. 

Direct photoreaction (eq 4) is important only for halocarbons (e.g., aromatic compounds) that significantly absorb radiation at wavelengths >295 nm, the cutoff for solar spectral irradiance at the earths surface. Because saturated chlorinated and fluorinated organic compounds, including methylchloroform and chlorofluorocarbons, absorb solar radiation very weakly, their direct photoreaction is very slow in the sea and in fresh waters. As discussed in a later section, photoreactions of these compounds may be accelerated by sorption and indirect photoreactions in natural waters. Saturated and olefinic poly-brominated and iodinated organic compounds have long absorption tails that extend beyond 295 nm. Direct photoreaction of such compounds in aquatic environments may be significant. 

Polyaniline (PANI) is a nonconductive polymer that could be rendered conductive by HCl doping. Several methods exist to accomplish such a doping. One of them is the incorporation of a chlorine-containing polymer into a polyaniline matrix and the irradiation of the resultant blend. Ionizing radiation (e-beam or y-irradiation) leads to the dehydrochlorination of the second polymer and the subsequent doping of the PANI (Figure 9.9). Several chlorine-containing polymers were tested in this approach, PVC, chlorinated polyisoprene, poly(vinylidene chloride-co-vinyl acetate), poly(vinylidene chloride-co-vinyl chloride). " ... 

Poly(vinyl chloride) is soluble in few solvents (tetrahydrofuran, cyclohexanone, etc.). An acetone-soluble polymerizate can be obtained by extensive post-chlorination of the PVC and this product contains 63-64% chlorine. Chlorinated PVC s are used as adhesives, lacquer bases, and industrial fibers. The chlorination occurs in solution at 60-100°C or in the gel state at 50°C. In the gel-state chlorination, PVC is swollen with chlorohydrocarbons and irradiated in aqueous suspension with UV light. Since CH2 groups are more easily chlorinated than CHCl groups, the polymer contains approximately equal proportions of- CHCl—CHCl and -f H2—CHCl groups. At an equal chlorine content, the PVC that was chlorinated as a gel possesses a higher glass-transition temperature, probably because of the stronger block copolymer character. 

Polystyrene [211, 279, 615, 1244, 1358, 1739, 2163, 2285-2290] and poly(a-methylstyrene) [211] dissolved in chlorinated solvents such as CHCI3, CHjCl, or CCI4 or doped as a film in CCI4 [2120] undergo rapid chain scission under UV irradiation. 

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