Other Sulfur-Containing Polymers

The polymer is highly crystalline, which facilitates structure analysis, but has thwarted attempts to measure its properties in solution. The preparation of single crystals has been useful with regard to the characterization of its structure. Its crystal structure is known, but not much is known about typical molecular weights. The S-N and N-S bonds are essentially identical in length, with a bond order that is intermediate 

For example, there is considerable interest in the preparation of sulfur-nitrogen polymers that have organic substituents on the sulfur atoms.56 This could help alleviate the intractability problem mentioned, and could also give rise to a series of polymers that parallel the phosphazenes in their structural variability. A series of polymers with S-N backbones of this type has been prepared, but with oxygen atoms as some of the substituents. The basic structure has the repeat unit -RS(=0)(N)- or -FS(=0)(N)-but they have not yet been studied in detail. The fluorine-containing polymer, however, is known to be a tough elastomer which is unaffected by water, acids, or bases up to 100 °C.7 

Because of the inorganic nature inherent in the strings of sulfur atoms in their backbones, these polymers have excellent resistance to hydrocarbon solvents that can swell common hydrocarbon elastomers. They also have good resistance to moisture, oxygen, and ozone, good weatherability, and better-than-average low temperature properties.62 

Materials prepared with liquid-like properties as mentioned above have molecular weights of only a few thousand. A variety of chemical curing agents are used to crosslink them, with Pb02 and chromates being good examples.62 

These polymers are typically prepared by reaction of sodium polysulfide with a formal. Bis(2-chloroelhy(formal) is commonly used, but some tn functional chlorinated hydrocarbon with its associated higher functionality is typically also added to promote branching. The sodium poly sulfide is usually made by the direct reaction of sodium hydroxide with sulfur at temperatures near 120 °C, as shown in reaction (9) 62 

---

The polymers [S]n and [SN] have been mentioned in Chapter 1. Other sulfur-containing polymers that have already been dealt with so far include those that have P-N-S and P-N-S(O) units as well as those that contain alternate S(0)N and PN units in the polymer backbone. In this section we will briefly look at polymers containing alternate sulfur and nitrogen atoms in the polymer backbone. In these pol5nners sulfur is hexavalent. An oxygen atom and an alky or an aryl group is present as the side-chain substituents on sulfur. 

Other Accelerators. Amine isophthalate and thiazolidine thione, which are used as alternatives to thioureas for cross-linking polychloroprene (Neoprene) and other chlorine-containing polymers, are also used as accelerators. A few free amines are used as accelerators of sulfur vulcanization these have high molecular weight to minimize volatility and workplace exposure. Several amines and amine salts are used to speed up the dimercapto thiadiazole cure of chlorinated polyethylene and polyacrylates. Phosphonium salts are used as accelerators for the bisphenol cure of fluorocarbon mbbers. 

Subsequent epidemiological studies have supported the association between better health and long-term consumption of diets rich in foods of plant origin. " However, whether this is because such diets minimize exposure to deleterious substances (e.g., oxidized cholesterol, pyrolysis mutagens, salt, saturated fat, etc.), or maximize intake of certain beneficial nutrients (e.g., isothiocyanates and other sulfur-containing plant constituents, mono-unsaturated fatty acids, and poly-unsaturated fatty acids, PPT, poly acetylenes, selenium, terpenes, etc.) or some combination as advocated in the Polymeal concept, remains unknown. " An in vitro study indicates that there may be mechanistic basis for true synergy between PPT and isothiocyanates. ... 

Small amounts of phosphorous can be used to vulcanize polymeric sulfur. Larger amounts yield the P4S4 bird-cage molecules mentioned in Section 6.2 on Other Phosphorous-Containing Polymers in Chapter 6, together with phosphorous-sulfur copolymers. The copolymers are hydrolytically unstable.56... 

Diphenylsulfone was not detected in the pyrolysate, either because it is not formed at detectable levels, or because it may not elute from the Carbowax column used for the separation of the pyrolysate. However, this compound and other sulfur-containing compounds may be formed during pyrolysis and not detected in the analysis step. The SO2 group represents 27.58% of the weight of the polymer, and only 19.94% molecular SO2 is detected in the pyrogram (assuming equal detector response for all analytes). The other sulfur-containing compounds except for diphenylsulfide (0.33%) and dibenzothiophene (0.72%) are at a trace levels. The thermal decomposition of PES takes place, very likely, by a radicalic mechanism, and the free radicals can interact and form other stable molecules such as biphenyl ( 4 % of volatile pyrolysate), 4-hydroxybiphenyl ( 2% of volatile pyrolysate) and dibenzofuran ( 12% of volatile pyrolysate) which are shown below ... 

Table 8 shows that over 50% binding of MADA (VIII) can be achieved in both NR and SBR by the mechanochemical procedure (21) and that this increases during vulcanization to about 70%. Other sulfur-containing antioxidants, VII and IX, can be bound to similar levels in both polymers. Figure 5 shows the effect of extraction on MADA-B in NR in comparison with a conventional thermal antioxidant, WSP (II), at 100 C. Similar results for SBR are listed in Table 9 before and after solvent extraction. The hindered phenolic antioxidant, BHBM-B is in general somewhat less effective than MADA-B, but is nevertheless much less affected by extraction than are conventional add it ives. 

Figure 5 displays the ITPD curves determined at 90 °C of PEEK, PES, and PPS films [27]. Both sulfur-containing polymer films exhibit a pronounced charge drain-off within the first 180 min and hence cannot be considered as electret materials. PEEK, on the other hand, shows a moderate surface potential decay and maintains around 50% charge after 24 h at 90°C. The charge storage characteristics of commercial polyimides and polyetherimide (Ultem 1000) films at 90 °C are displayed in Fig. 6. Kapton HN (PI) films lose almost the complete surface potential within 24 h, exhibiting a steep decay in the first minutes. Upilex R renders better results, since its potential decay is moderate and after 24 h around 45% of the applied charge...

In other investigations, several cyclic sulfides were foimd to be present in the corresponding sulfur-containing polymers, and FAB-MS allowed the identification of all the oligomers resolved in the SEC traces. ... 

One class of aromatic polyethers consists of polymers with only aromatic rings and ether linkages ia the backbone poly(phenylene oxide)s are examples and are the principal emphasis of this article. A second type contains a wide variety of other functional groups ia the backbone, ia addition to the aromatic units and ether linkages. Many of these polymers are covered ia other articles, based on the other fiinctionahty (see Polymers containing sulfur, POLYSULFONES). 

Cyanide blood agents are relatively unstable and tend to polymerize on standing. Polymers can be explosive. Stabilizers or solvents can be added to inhibit decomposition. Stabilizers include phosphoric acid, sulfuric acid, powdered sodium pyrophosphate, and sulfur dioxide. Although cyanide blood agents react with metals, they can be stored in steel or other common containers if stabilized. 

The polymeric phosphazenes are treated in chapter (see Polyphosphazenes) A recent monograph covers the chemistry of polyphosphazenes (nomenclature, synthesis of cyclic monomers , ring opening polymerization, condensation polymerization, substitution, polymer properties, and applications more than 1000 literature citations). Other reviews have also been published recently. Sulfur-containing polyphosphazenes have also been described. ... 

After equilibration liquid sulfur contains a certain concentration of polymeric molecules (Soo) at all temperatures. This polymer can be isolated and determined by quenching the melt at very low temperatures, extracting the smaller molecules immediately by pure carbon disulfide at 20 °C, and drying the residue of S in a vacuum. Extraction and drying should be done with exclusion of light and nucleophiles and avoiding higher temperatures which would initiate the conversion of the polymer to cyclo-Ss. The content of jx-sulfur thus obtained depends on the purity of the melt. In addition, it has to be obeyed that the r-sulfur present in the quenched melt is unstable at 20 °C and partly polymerizes to S for which reason the extraction has to be done without any delay if the true polymer content of the melt is to be determined. If, on the other hand, simply S is to be prepared it is possible to in-... 

---