Linked Aliphatic Polysulfides

The simplest chain structure -f-CH2—S- occurs through the polymerization of thioformaldehyde, CH2S, or its cyclic trimer (trithiane). Aliphatic polysulfides with two or more carbon atoms per monomeric unit are available through the polymerization of cyclic sulfides. The start step with organolithium compounds deviates from that of the epoxides in that initially the sulfur atom is attacked and subsequently the carbon atom is attacked. For example, the starting step with propylene sulfide and ethyl lithium initially gives propylene and lithium ethane thiolate  

the thiolate anion polymerizes the excess propylene sulfide  

The polymerization of four-membered rings, however, proceeds directly through the formation of carbanions  

A monomer can be obtained from pentaerythritol, C(CH20H)4, and chloroacetaldehyde, CICH2CHO, which leads to sulfur-containing polymers when polycondensed with disodium sulfide  

The end groups are capped with ethylene chlorohydrin to stabilize them. The polymeric substance becomes thermoplastic at 200-260°C and can be processed to tough films at this temperature. 

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Monosulfur-linked aliphatic polysulfides have the general constitutional formula, -(-R — S-), where R is an aliphatic or cycloaliphatic residue. The simplest chain structure, -(-CH2—S- h, is produced by polymerizing thio-formaldehyde, HCHS, or its cylic trimer, trithiane. Since the polymer readily decomposes to the monomer, it has only academic interest. 

Poly sulfide Polymers. These polymers are made up of aliphatic hydrocarbon units connected by di-, tri- or tetrasulfide links. The synthetic rubber found useful in ordn has hydrocarbon units linked by either O or formal segments. The polymers are usually prepd by the condensation of a suitable organic dihalide, usually the chloride, with aq Na polysulfide. According to Ref 8, the most practical organic dichloride is dichlorodiethylformal viz, Bis[ 2[Pg.827]

Flexiblization. Aliphatic diepoxide reactive diluents enhance the flexibility or elongation by providing chain segments with greater free rotation between cross-links. Polyaminoamide hardeners, based on aliphatic polyamines and dimerized fatty acids, perform similarly. Liquid polysulfide polymers possessing terminal mercaptan functionality improve impact properties in conjimction with polyamine hardeners. 

Since Activator 73 A is a mixture of zinc salts of linear aliphatic and aromatic carboxylic acids (50), it would be expected that the mechanism of action would be similar to zinc stearate, which can extract sulfur from polysulfidic cross-links and reuse that sulfur to generate more cross-links (51). Ultimately this would result in a network structure high in monosulfidic content (42). 

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