Halogenated resists

Table IV compares the X-ray exposure characteristics (at 8.3 X, Al Kai,2 emission line) of the halogenated resists and of PMMA Elvacite 20U1. It can be seen that poly(2-ehloroethyl methacrylates) and poly(2-bromoethyl methacrylates) exhibit a low sensitivity unlike poly(2-fluoroethyl methacrylates) and poly(2-, 2-,2-trifluoroethyl methacrylates) which are more sensitive than PMMA as shown in Figures 2a, 2b, 2c, 2d where the dose-thickness curves of these resists are plotted. The low sensitivity of the PC1EMA and PBrEMA samples may be explained by some competing crosslinking reactions which could occur during exposure as a result of C-Cl and C-Br homolytic bond scissions as noted by Tada...

Initially all membranes were exposed to 3 ppm chlorine in buffer solutions at pH levels of 3.0, 5.8, and 8.6 for three weeks. Both cellulose acetate type membranes C-2 and V-1 were unaffected by chlorine under these conditions. Continued exposure at higher chlorine levels did not alter baseline membrane performance. For example, membrane C-2 exposed to 125 ppm chlorine for 10 days at pH 3 continued to perform at baseline levels. In subsequent work, cellulose acetate membranes were also found to be unresponsive to bromine, iodine, and chlorine dioxide. It can be generally concluded that cellulose acetate type membranes are halogen resistant. 

Further work should be directed at better understanding the nature of halogen-membrane interaction. These efforts may provide guidelines for development of more halogen resistant membranes. 

Other halogenated resist systems include partially chlorinated, narrow dispersity poly (vinyl-toluene). The latter differs from the CMS resist above in that chlorine is substituted on the main chain as well as on the pendant methyl group (44). 

We note from Table VIII a strong interest in halogenated resists, particularly those substituted with chlorine. The addition of chlorine to the aromatic structure of polystyrene has a marked effect on cross-linking efficiency. Monodisperse polystyrene, for example, has a sensitivity on the order of 50 p C/cm2, yet with as little as 20% chloromethyl groups substituted on the ring, the sensitivity is improved to 2 C/cm2 for comparable molecular weight and distribution. 

The 4-position is the most benzenelike and a 4-halogen resists nucleophilic attack with the exception of the formation of nitriles with cuprous cyanide9,70,93,94,99 and one case of the formation of a lithium derivative (see Section III,B). Halogen exchange has been observed during the diazotization of a 5-amino-4-bromoisothiazole in the presence of concentrated hydrochloric acid.119... 

Tolerance to chlorine The destruction of current polyamide membranes upon exposure to oxidizers is a significant handicap when trying to treat water sources such as surface water (lakes and rivers) and wastewater. These feed sources contain biological materials and nutrients to propagate microbes that severely foul RO membranes. Development of halogen-resistant membranes is vitally important as more challenging feed waters are treated by RO. 

Detailed descriptions of a halogen resistant catalyst are presented by Lester (1989) and Summers et al. (1989). Figure 13-8, which appears in both papers, shows conversion efficiency curves for the destruction of C-1 chlorocarbons over Allied Signal HDC Catalyst. The ease of destruction is shown to increase as the number of chlorine atoms in the molecule increases. Tests reported by these authors also showed the HDC Catalyst to provide higher conversion efficiency (or to operate at lower temperature for the same conversion efficiency) than a chromia-alumina catalyst operated at the same space velocity with feed ga.ses containing various chlorinated and aromatic hydrocarbons. Herbert (1991) presents data that show essentially no change in performance for the HDC Catalyst when operated for 1,600 hours at 215°C with a gas stream containing 1,(X)0 ppm carbon tetrachloride, 9.8 vol.% water, and the balance air. 

Combustion in an incinerator is the only practical way to deal with many waste streams.This is particularly true of solid and concentrated wastes and toxic wastes such as those containing halogenated hydrocarbons, pesticides, herbicides, etc. Many of the toxic substances encountered resist biological degradation and persist in the natural environment for a long period of time. Unless they are in dilute aqueous solution, the most effective treatment is usually incineration. 

The iodine atom in iodobenzene (unlike that in the corresponding aliphatic compounds) is very resistant to the action of alkalis, potassium cyanide, silver nitrite, etc. This firm attachment of the iodine atom to the benzene ring is typical of aromatic halides generally, although in suitably substituted nitio-compounds, such as chloro-2,4-dinitrobenzene, the halogen atom does possess an increased reactivity (p. 262). 

Ruthenium is a hard, white metal and has four crystal modifications. It does not tarnish at room temperatures, but oxidizes explosively. It is attacked by halogens, hydroxides, etc. Ruthenium can be plated by electrodeposition or by thermal decomposition methods. The metal is one of the most effective hardeners for platinum and palladium, and is alloyed with these metals to make electrical contacts for severe wear resistance. A ruthenium-molybdenum alloy is said to be... 

Hafnium is resistant to concentrated alkalis, but at elevated temperatures reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Halogens react directly to form tetrahalides. 

Unsaturated Polyesters. There are two approaches used to provide flame retardancy to unsaturated polyesters. These materials can be made flame resistant by incorporating halogen when made, or by adding some organic halogen compound when cured. In either case a synergist is needed. The second approach involves the addition of a hydrated filler. At least an equal amount of filler is used. 

Olefin Polymers. The flame resistance of polyethylene can be increased by the addition of either a halogen synergist system or hydrated fillers. Similar flame-retarder packages are used for polypropylene (see Olefin polymers). Typical formulations of the halogen synergist type are shown in Table 15 the fiUer-type formulations are in Table 16. 

Reactions With Metals. AH metals react to some extent with the halogen fluorides, although several react only superficiaHy to form an adherent fluoride film of low permeabHity that serves as protection against further reaction. This protective capacity is lost at elevated temperatures, however. Hence, each metal has a temperature above which it continues to react. Mild steel reacts rapidly above 250°C. Copper and nickel lose the abHity to resist reaction above 400 and 750°C, respectively. 

The high fluorine content contributes to resistance to attack by essentially all chemicals and oxidizing agents however, PCTFE does swell slightly ia halogenated compounds, ethers, esters, and selected aromatic solvents. Specific solvents should be tested. PCTFE has the lowest water-vapor transmission rate of any plastic (14,15), is impermeable to gases (see also Barrierpolymers), and does not carbonize or support combustion. 

Halogenated hydrocarbons that are inexpensive sometimes are used alone or in blends with phosphate esters as fire-resistant hydrauHc fluids. Other halogenated fluids are used for oxygen-compressor lubricants, lubricants for vacuum pumps that are in contact with corrosive materials, solvent-resistant lubricants, and other lubricant appHcations where highly corrosive or reactive materials are being handled. 

Blends ofiPetramethylbisphenolA-PC (TMBPA-PC) with ModfiedPS or Styrene-Ac7ylonitrile(SAN) Copolymer. By installing halogen atoms on the aromatic rings of the PC-backbone, not only the resistance to heat softening can be increased (eg, TMBPA-PC = 203° C) (209), but also the compatibiUty with olefins. 

---