POLY(ETHYLENE)

Chemical properties

light yellow waxy solid

Chemical properties

Before vulcanization, chlorosulphonated polyethylene is a tacky, rubbery material oflow tensile strength; it is soluble in chlorinated hydrocarbons. The sulphonyl chloride groups are reactive and may be used for cross-linking the polymer. Vulcanization is generally carried out by heating with metal oxides such as litharge or magnesium oxide in the presence of a little water. Reaction probably proceeds as follows:

The cross-linked product has good resistance to chemical attack, especially attack by ozone, oxygen and other oxidizing agents. As a rubber, the material has excellent mechanical properties and these are maintained over long periods of use at elevated temperatures. The rather, high cost of the material limits its use to such applications as sheeting and wire and cable coating intended for service in demanding conditions.

The Uses of POLY(ETHYLENE)

POLY(ETHYLENE) can be used for rubber hose;electric wire and cable;special synthetic rubber;wires and cables.

Production Methods

This type of elastomer is made by dissolving polyethylene in carbon tetrachloride and then treating it with chlorine and sulfonyl chloride in the presence of a catalyst. After the desired degree of chlorosulfonation has been attained, the residual chlorine–sulfur dioxide mixture is stripped off, a stabilizer is added, and the commercial product is isolated as raw rubber in crumb or film form.

Preparation

In the preparation of chlorosulphonated polyethylene the polymer (commonly, a low density polyethylene with molecular weight (Mn) of about 20000) is treated with chlorine in the presence of a small amount of sulphur dioxide. Typically, the reaction is carried out in solution in hot carbon tetrachloride. Both chloride and sulphonyl chloride groups are introduced into the polymer, the degree of substitution and the ratio of the two types of groups depending on the reaction conditions. Commercial products generally contain about 30% chlorine and 1.5% sulphur, which corresponds to approximately one chlorine group per 7 carbon atoms and one sulphonyl chloride group per 85 carbon atoms. Such a product may be represented as follows:

Industrial uses

This material, more commonly known as Hypalon,can be compounded to have an excellentcombination of properties including virtuallytotal resistance to ozone and excellent resistanceto abrasion, weather, heat, flame, oxidizingchemicals, and crack growth. In addition,the material has low moisture absorption, gooddielectric properties, and can be made in a widerange of colors because it does not require carbonblack for reinforcement. Resistance to oilis similar to that of neoprene. Low-temperatureflexibility is fair at –40°C.
The material is made by reacting polyethylenewith chlorine and SO2 to yield chlorosulfonatedpolyethylene. The reaction changes thethermoplastic polyethylene into a synthetic elastomerthat can be compounded and vulcanized.The basic polyethylene contributes chemicalinertness, resistance to damage by moisture, andgood dielectric strength. Inclusion of chlorinein the polymer increases its resistance to flame(makes it self-extinguishing) and contributes toits oil and weather resistance.