A pyrolysis gas chromatography method was developed to determine the composition and microstructure of chlorinated polyethylene (CPE). This method utilized specific aromatic compounds which were formed through dehydrochlorination of trimers after pyrolysis of CPE polymers at elevated temperatures. The composition and microstructure calculation was based on the difference between the levels of ethylene and vinyl chloride trimers formed. This method is valid for CPE polymers containing between 25 and 48 wt % chlorine. The composition of CPE polymers used in this study was corroborated with 13 C-NMR results and the manufacturer's product specification.Chlorinated polyethylene (CPE) is a polyethylene that has random chlorine substitution. The use and commercialization of halogen substitution (especially chlorine substitution) to improve the toughness and barrier properties, as well as ignition resistance, of long-chain hydrocarbon polymers originated in the United States in the early 1950s. Depending on the degree of chlorination, CPE polymers can have elastomeric and thermoplastic forms which have extraordinary compatibility with a range of other materials. This makes CPE readily adaptable to common compounding and curing techniques. CPE polymers can produce end products that are hard and tough or soft and flexible. Most commercial CPE products contain 25-50 wt % chlorine.CPE is an ignition-resistant polyethylene. It is also used in blends to change the ignition characteristics of other polymers. CPE has no unsaturation in the polymer backbone, giving it excellent ozone and weathering properties. The saturated backbone also results in a temperature stability that allows CPE to perform well continuously at temperatures of 150 °C. CPE can provide satisfactory resistance to most acids, bases, oils, and alcohols. CPE polymers are well known for their impact resistance, abrasion resistance, and resistance to mechanical damage.Because CPE polymers have good heat resistance, chemical resistance, and mechanical properties, their major applications are in automotive hose, tubing, and wire jacketing. Other applications include roofing, gaskets, tank linings, and molded goods. The only disadvantage of CPE is its sensitivity to temperatures above 200 °C.The chlorination reaction of polyethylene can be expressed as