Poly irradiated

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

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). 

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. 

Liquid trichloroethylene has been polymerized by irradiation with Co y-rays or 20-keV x-rays (9). Trichloroethylene has a chain-transfer constant of <1 when copolymerized with vinyl chloride (10) and is used extensively to control the molecular weight of poly(vinyl chloride) polymer. 

These pioneer studies laid dormant until 1977 and, influenced by Kondo and colleagues [59] reports on the synthesis of po]y(vinylsulfonium yiide) with a trivaient sulfur attached directly to the polymer chain, poly[ethyl-vinylsulfonium bis-(methoxycarbonyl) methylide] (Scheme 25) was prepared by irradiation of a benzene... 

Polyethylene films were preirradiated with gamma-rays and again irradiated in aqueous poly(vinyI alcohol) solutions to give water lubricated antifriction films [121]. 

Problem 31.7 1 Irradiation of poly(-l,3-butadiene), followed by addition of styrene, yields a graft copolymer that is used to make rubber soles for shoes. Draw the structure of a representative segment of this styrene-butadiene graft copolymer. 

There are several other interesting polymers forming SAH with swellings up to 1500 ml g 1 under irradiation in aqueous solutions, such as sodium salts of PAAc [83], copolymers of AAm with AAc [22], poly-N-vinylpyrrolidone [84], PVA... 

Fig. 16. Change of optical density (JD) of aqueous solutions of poly (potassium propynoate) for different wavelengths in the process of oxidation during irradiation with white light...

Fig. 20. Increase of the intensity of the ESR signal during the irradiation and its decay in darkness of a bromine complex of a poly(schiff base) prepared by polycondensation of 4,4 -diacetyldiphenyl sulfide and p-phenyienediamine mole ratio 1 S.8...

Bond strength data for four multilayered materials is shown in Table V. In each case the data is for the bond between the food-contacting layer and its adjacent layer. In Pouch 1, it is the bond between ethylene-butene copolymer and aluminum foil in Pouch 2 between ethylene-butene copolymer—polyisobutylene blend and aluminum foil in Pouch 3 between ethylene-butene copolymer and polyiminocaproyl and in Pouch 4 between ethylene-butene copolymer and poly(ethylene terephthalate). Bond strength increased in the four multilayered materials after the irradiation treatment. 

However, Pacansky and his coworkers77 studied the degradation of poly(2-methyl-l-pentene sulfone) by electron beams and from infrared studies of the products suggest another mechanism. They claim that S02 was exclusively produced at low doses with no concomitant formation of the olefin. The residual polymer was considered to be essentially pure poly(2-methyl-l-pentene) and this polyolefin underwent depolymerization after further irradiation. However, the high yield of S02 requires the assumption of a chain reaction and it is difficult to think of a chain reaction which will form S02 and no olefin. 

Maleimides Alkyl and aryl maleimides in small concentrations, e.g., 5-10 wt% significantly enhance yield of cross-link for y-irradiated (in vacuo) NR, cw-l,4-polyisoprene, poly(styrene-co-butadiene) rubber, and polychloroprene rubber. A-phenyhnaleimide and m-phenylene dimaleimide have been found to be most effective. The solubihty of the maleimides in the polymer matrix, reactivity of the double bond and the influence of substituent groups also affect the cross-fink promoting ability of these promoters [82]. The mechanism for the cross-link promotion of maleimides is considered to be the copolymerization of the rubber via its unsaturations with the maleimide molecules initiated by radicals and, in particular, by allyfic radicals produced during the radiolysis of the elastomer. Maleimides have also been found to increase the rate of cross-linking in saturated polymers like PE and poly vinylacetate [33]. 

Temperature dependence (related to the temperature dependence of the conformational structure and the morphology of polymers) of the radiation effect on various fluoropolymers e.g., poly (tetrafluoroethylene-co-hexafluoropropylene), poly(tetrafluoroethylene-co-perfluoroalkylvinylether), and poly(tetrafluoroethylene-co-ethylene) copolymers has been reported by Tabata [419]. Hill et al. [420] have investigated the effect of environment and temperature on the radiolysis of FEP. While the irradiation is carried out at temperatures above the glass transition temperature of FEP, cross-linking reactions predominate over chain scission or degradation. Forsythe et al. [421]... 

SCHEME 31. S (a) Oxidation, dehydrofluorination and crosslinking reactions as a result of EB irradiation of poly (vinylidenefluoride-co-hexafluoropropylene-co-tetrafluoroethylene). (b) Chain scission reactions as a result of EB irradiation of poly (vinylidenefluoride-co-hexafluoropropylene-co-tetrafluoroethylene). 

Thus, the photo-activity of poly[bis(4-benzoylphenoxy)phosphazene] under illumination could be finely tuned by irradiating the polymer in the presence of variable amount of naphthalene, a typical triplet state energy quencher [474]. The same polymer could be used as polymeric photosensitizer to induce the... 

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