Poly-sulphides

Poly(methylene disulphide), poly(methylene tetrasulphide), poly(ethylene disulphide) and poly(ethylene tetrasulphide) are photodegraded under UV irradiation with the formation of carbon monosulphide (CS), carbon disulphide (CS2) and hydrogen sulphide (HS) according to the mechanism [1047, 1971]  

The photolysis of the poly(methylene polysulphides) yields about 100 times more carbon disulphide than the poly(ethylene polysulphides) [1047]. 

The quantum yield of chain cleavage = 0.16-0.21 for poly(propylene disulphide), 0.19 for poly(propylene sulphoxide) and 0.05-0.09 for poly-(propylene sulphide) [1971]. 

Photolysis of polysulphone 4.84) prepared from the polycondensation of bisphenols (e.g. 2,2-bis-(4-hydroxyphenyl)propane) with 4,4 -dichlorodiphenyl-sulphone occurs by the following mechanism [4, 79, 740]  

UV irradiation in vacuum or in air (oxygen) yields a number of gaseous products (Table 4.6). 

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More interest has been shown in polymeric flexibilisers, particularly the low molecular weight polyamides from dimer acid (see Chapter 18), the low molecular weight poly sulphides (Chapter 19), polyamines and the polyglycol diepoxides. 

This group of synthetic elastomers is better known under the trade name ThiokoP. Polysulphide rubbers are condensation polymers of sodium poly sulphide and dichloro-compounds they have outstanding resistance to swelling by oils and solvents but tensile strength is... 

Fuerstenau (1980) found that sulphide minerals are naturally floatable in the absence of oxygen. Yoon (1981) ever attributed the natural floatability of some sulphide minerals to their very low solubility. Finkelstein et al. (1975) considered that the natural floatability of sulphide minerals are due to the formation of elemental sulphur and related to the thickness of formation of elemental sulphur at the surface. Some authors reported that the hydrophobic entity in collectorless flotation of sulphide minerals were the metal-deficient poly sulphide (Buckley et al., 1985). No matter whichever mechanism, investigators increasingly concluded that most sulphide minerals are not naturally floatable and floated only under some suitable redox environment. Some authors considered that the natural floatability of sulphide minerals was restricted to some special sulphide minerals such as molybdenite, stibnite, orpiment etc. owing to the effects of crystal structure and the collectorless floatability of most sulphide minerals could be classified into self-induced and sulphur-induced floatability (Trahar, 1984 Heyes and Trahar, 1984 Hayes et al., 1987 Wang et al., 1991b, c Hu et al, 2000). 

Fig. 10.3 Modulated electrotransmission (ET) and electroreflectance (ER) spectra of a CD CdSe film deposited from an NTA/selenosulphate bath at 30°C. The experiments were carried out in an electrolyte containing sulphide and sulphite (the latter to prevent formation of colored poly sulphide) at a pH of 10 (buffered with NaH2P04). 

Virtually nothing is known about the lithium poly sulphides. Sodium tetrasulphide is the highest stable sodium polysulphide, although higher ones may be present in... 

An alternative method of representing the formula of the poly-sulphides has been proposed,5 namely... 

It should be recognized that appreciable shifts in bonding strength are sometimes made possible by special compounding variations for instance, the heat resistance of NR vulcanizates may be improved considerably by variation of the vulcanizing system. The normal sulphur vulcanization system is capable of many variants, which will govern the chemical nature of the sulphur cross link, i.e., whether it is essentially a more, di, or poly-sulphide type. The nature of sulphur cross link can have considerable influence on the bond strength and the heat-resistance of vulcanizate... 

According to A. F. de Fourcroy,4 if the vapour of sulphur and ammonia be led through a red-hot tube, hydrogen, nitrogen, and a crystalline mixture of ammonium mono- and poly-sulphides are formed. F. Jones said that dry sulphur absorbs ammonia, and when the product is heated, ammonium sulphide is formed. A. Smith and W. B. Holmes found that if ammonia gas be passed over molten sulphur no insoluble sulphur is formed during the cooling. C. A. Seely found that liquid... 

The meaning of the symbols is the following (A) , Aliphatic poly(oxides) O, Aliphatic poly(sulphides) ... 

FIG. 6.7 Ym as a function of the number of -CH2- groups in the main chain. The meaning of the symbols is the following (A) , Aliphatic poly(oxides) O, Aliphatic poly(sulphides) A, Aliphatic poly(carbonates) ... 

IV.6 SULPHIDES, S2 Solubility The acid, normal, and poly-sulphides of alkali metals are soluble in water their aqueous solutions react alkaline because of hydrolysis. 

The solution of the sulphide in water has an alkaline reaction due to hydrolytic dissociation. Atmospheric oxygen converts the dissolved sulphide into thiosulphate, and electrolytic oxidation yields the sulphate. The solution dissolves sulphur, forming poly sulphides. 

Silver sulphide, Ag2S.—The sulphide occurs in nature as argentite, and also in combination with many other sulphides. It is formed by direct synthesis from its elements at ordinary temperatures,7 and also by immersion of the metal in solutions of alkali-metal poly sulphides. It can be prepared in cubic crystals by passing sulphur-vapour over heated silver, or by the action of hydrogen trisulphide, H2S3, on silver oxide. It is the only definite compound produced by fusion of mixtures of silver and sulphur in different proportions.9 The black, amorphous form is precipitated by the action of hydrogen sulphide or a soluble sulphide on a solution of a silver salt. It is also produced by the action of hydrogen sulphide on metallic silver, a reversible reaction.10... 

Add ammonium poly sulphide solution and evaporate to dryness on a water-badi. To die residue add a few drops of dilute hydrochloric acid, filter, and to the filtrate add a few drops oiferric chloride solution. A deep red colour due to ferric thiocyanate indicates the presence of cyanide. 

Black GeS is formed by reducing GeSg in hydrogen at 500". SnS is obtained as a grey solid by heating the metal with sulphur at 900, or as a brown precipitate when HgS is passed into a tin (II) salt solution. It does not dissolve in alkali sulphides but in poly sulphides, such as yellow ammonium sulphide, it gives solutions of thiostannates from which the higher sulphide is precipitated on acidification. 

The photoelectron spectrum and ab initio SCF calculations of sulphur dichloride have been presented, and an assignment of observed states of the SCF radical cation was attempted.71 For the SC12 ground state the calculated dissociation energy, dipole moment, total atomic population, and total d -orbital population were given. The photolysis of sulphur monochloride with a series of saturated aliphatic hydrocarbons has been shown to yield alkyl chlorides, di- and poly-sulphides, hydrogen chloride, and elemental sulphur.72... 

While this cell utilised a salt bridge to separate the two electrolytes, many systems used a membrane instead. Ang and Sammells (1980) provided an example of a membrane cell with a polycrystalline n-CdSe photoelectrode that drove a poly-sulphide/polyselenide storage couple. The cell had reasonable conversion efficiency (4%), but low output power density. The storage reaction and cell configuration are ... 

Terminal Group Terminal Group of Poly sulphide of Epoxide... 

The low molecular weight poly sulphides have found somewhat greater use. Of general structure HS—R—SH and with molecular weights of approximately 1000 they will react with the epoxy group to cause chain extension but not cross-linking. The normal hardeners must therefore be employed in the usual amounts... 

Polyacetylene and other organic polymer semiconductors have been in the news recently, and MacDiarmid and Heeger have used polyacetylene photoanodes in a poly sulphide solar cell. Poly acetylene and other organic polymers have also been used in solid-state photovoltaic cells, but conversion efficiencies are still very low. 

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