Hypalon
Hypalon is a chlorosulfonated polyethylene synthetic rubber noted for its resistance to chemicals, temperature extremes, and ultraviolet light. It was a product of DuPont Performance Elastomers, a subsidiary of DuPont. Hypalon as it is now known in the marine industry today is a remarketed version of the old Hypalon using an additional layer of neoprene so the new chemical formulation is csm/cr.
Chemical structure
Polyethylene is treated with a mixture of chlorine and sulfur dioxide under UV-radiation. The product contains 20-40% chlorine. The polymer also contains a few percent chlorosulfonyl groups. These reactive groups allow for vulcanization, which strongly affects the physical durability of the products. An estimated 110,000 tons/y were produced in 1991.Synthesis
Typically, low-density polyethylene or high-density polyethylene serves as the raw material. The polymer is treated with chlorine gas and sulfur dioxide, or alternatively with sulfuryl chloride, in the presence of a radical initiator.The reaction follows a free-radical substitution mechanism. Chlorine atoms replace hydrogen along the chain, disrupting the crystallinity of the polyethylene and providing elastomeric properties. Simultaneously, sulfonyl chloride groups are introduced, which serve as reactive sites for cross-linking.
The general reaction can be represented as:
Commercial grades typically contain 20–45% chlorine and 1–2% sulfur by weight.
Cross-linking (Curing)
Unlike natural rubber, which is typically vulcanized using sulfur, CSM is cured using metal oxides. The sulfonyl chloride groups react with the metal oxide—typically magnesium oxide, lead(II) oxide, or zinc oxide —in the presence of accelerators and fatty acids to form stable cross-links.The cross-linking mechanism forms a metal sulfonate bridge: